ABSORPTION OF DRUGS Prof. Dr. Basavaraj K. Nanjwade M. Pharm., Ph. D Department of Pharmaceutics KLE University’s College of Pharmacy BELGAUm – 590010, Karnataka, India Cell No: 00919742431000 E-mail: bknanjwade@yahoo.co.in 08/10/2010 KLECOP, Nipani

CONTENTS Introduction of absorption. Structure of the Cell Membrane. Gastro intestinal absorption of drugs. Mechanism of Drug absorption. Factors affecting drug absorption Absorption of drugs from non-per oral routes Methods of determining absorption References. 08/10/2010 KLECOP, Nipani

Introduction of Absorption Definition : The process of movement of unchanged drug from the site of administration to systemic circulation. There always exist a correlation between the plasma concentration of a drug & the therapeutic response & thus, absorption can also be defined as the process of movement of unchanged drug from the site of administration to the site of measurement. i.e., plasma. 08/10/2010 KLECOP, Nipani

Therapeutic success of a rapidly & completely absorbed drug. Not only the magnitude of drug that comes into the systemic circulation but also the rate at which it is absorbed is important this is clear from the figure. Plasma Drug Conc. Minimum effective conc. Therapeutic failure of a slowly absorbed drug. Subtherapeutic level Time 08/10/2010 KLECOP, Nipani

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CELL MEMBRANE Also called the plasma membrane, plasmalemma or phospholipid bilayer. The plasma membrane is a flexible yet sturdy barrier that surrounds & contains the cytoplasm of a cell. Cell membrane mainly consists of: 1. Lipid bilayer- -phospholipid -Cholesterol -Glycolipids. 2. Proitens- -Integral membrane proteins -Lipid anchored proteins -Peripheral Proteins 08/10/2010 KLECOP, Nipani

LIPID BILAYER 08/10/2010 KLECOP, Nipani

LIPID BILAYER The basic structural framework of the plasma membrane is the lipid bilayer. Consists primarily of a thin layer of amphipathic phospholipids which spontaneously arrange so that the hydrophobic “tail” regions are shielded from the surrounding polar fluid, causing the more hydrophilic “head” regions to associate with the cytosolic & extracellular faces of the resulting bilayer. This forms a continuous, spherical lipid bilayer app. 7nm thick. 08/10/2010 KLECOP, Nipani

It consists of two back to back layers made up of three types: Phospholipid, Cholesterol, Glycolipids. Phospholipids : Principal type of lipid in membrane about 75 %. Contains polar and non polar region. Polar region is hydrophilic and non polar region is hydrophobic. Non polar head contain two fatty acid chain. One chain is straight fatty acid chain.( Saturated ) Another tail have cis double bond and have kink in tail. ( Unsaturated ) 08/10/2010 KLECOP, Nipani

CHOLESTEROL Amount in membrane is 20 %. Insert in membrane with same orientation as phospholipids molecules. Polar head of cholesterol is aligned with polar head of phospholipids. FUNCTION: Immobilize first few hydrocarbons groups phospholipids molecules. Prevents crystallization of hydrocarbons & phase shift in membrane 08/10/2010 KLECOP, Nipani

NON - POLAR HYDROCARBON CHAIN OH RIGID STEROID REGION POLAR REGION 08/10/2010 KLECOP, Nipani

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GLYCOLIPIDS Another component of membrane lipids present about 5 %. Carbohydrate groups form polar “head”. Fatty acids “tails” are non polar. Present in membrane layer that faces the extracellular fluid. This is one reason due to which bilayer is asymmetric. FUNCTIONS: Protective Insulator Site of receptor binding 08/10/2010 KLECOP, Nipani

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COMPOSITION OF PROTEINS 08/10/2010 KLECOP, Nipani

INTEGRAL PROTEINS Also known as “Transmembrane protein”. Have hydrophilic and hydrophobic domain. Hydrophobic domain anchore within the cell membrane and hydrophilic domain interacts with external molecules. Hydrophobic domain consists of one, multiple or combination of α – helices and ß – sheets protein mofits. Ex. – Ion Channels, Proton pump, GPCR. 08/10/2010 KLECOP, Nipani

LIPID ANCHORED PROTEIN Covalently bound to single or multiple lipid molecules. Hydrophobically inert into cell membrane & anchor the protein. The protein itself is not in contact with membrane. Ex. – G Proteins. 08/10/2010 KLECOP, Nipani

PERIPHERAL PROTEINS Attached to integral membrane proteins OR associated with peripheral regions of lipid bilayer. Have only temporary interaction with biological membrane. Once reacted with molecule, dissociates to carry on its work in cytoplasm. Ex. – Some Enzyme, Some Hormone 08/10/2010 KLECOP, Nipani

GASTRO INTESTINAL ABSORPTION OF DRUGS 08/10/2010 KLECOP, Nipani

Stomach : The surface area for absorption of drugs is relatively small in the stomach due to the absence of macrovilli & microvilli. Extent of drug absorption is affected by variation in the time it takes the stomach to empty, i.e., how long the dosage form is able to reside in stomach. Drugs which are acid labile must not be in contact with the acidic environment of the stomach. Stomach emptying applies more to the solid dosage forms because the drug has to dissolve in the GI fluid before it is available for absorption. Since solubility & dissolution rate of most drugs is a function of pH, it follows that, a delivery system carrying a drug that is predominantly absorbed from the stomach, must stay in the stomach for an extended period of time in order to assure maximum dissolution & therefore to extent of absorption. 08/10/2010 KLECOP, Nipani

Small Intestine : The drugs which are predominantly absorbed through the small intestine, the transit time of a dosage form is the major determinant of extent of absorption. Various studies to determine transit time: Early studies using indirect methods placed the average normal transit time through the small intestine at about 7 hours. These studies were based on the detection of hydrogen after an oral dose of lactulose. (Fermentation of lactulose by colon bacteria yields hydrogen in the breath). 08/10/2010 KLECOP, Nipani

Small Intestine : Newer studies suggest the transit time to be about 3 to 4 hours. Use gamma scintigraphy. Thus, if the transit time in small intestine for most healthy adults is between 3 to 4 hours, a drug may take about 4 to 8 hours to pass through the stomach & small intestine during fasting state. During the fed state, the small intestine transit time may take about 8 to 12 hours. 08/10/2010 KLECOP, Nipani

Large intestine : The major function of large intestine is to absorb water from ingestible food residues which are delivered to the large intestine in a fluid state, & eliminate them from the body as semi solid feces. Only a few drugs are absorbed in this region. 08/10/2010 KLECOP, Nipani

MECHANISM OF DRUG ABSORPTION Passive diffusion Pore transport Carrier- mediated transport a) Facilitated diffusion b) Active transport Ionic or Electrochemical diffusion Ion-pair transport Endocytosis 08/10/2010 KLECOP, Nipani

PASSIVE DIFFUSION Also known as non-ionic diffusion. It is defined as the difference in the drug concentration on either side of the membrane. Absorption of 90% of drugs. The driving force for this process is the concentration or electrochemical gradient. 08/10/2010 KLECOP, Nipani

dQ = D A Km/w (CGIT – C) dt h Passive diffusion is best expressed by Fick’s first law of diffusion which states that the drug molecules diffuse from a region of higher concentration to one of lower concentration until equilibrium is attained & the rate of diffusion is directly proportional to the concentration gradient across the membrane. dQ = D A Km/w (CGIT – C) dt h Certain characteristic of passive diffusion can be generalized. Down hill transport 08/10/2010 KLECOP, Nipani

Greater the surface area & lesser the thickness of the membrane, faster the diffusion. Equilibrium is attained when the concentration on either side of the membrane become equal. Greater the membrane/ water partition coefficient of drug, faster the absorption. Passive diffusion process is energy independent but depends more or less on the square root of the molecular size of the drugs. The mol. Wt. of the most drugs lie between 100 to 400 Daltons which can be effectively absorbed passively. 08/10/2010 KLECOP, Nipani

Pore transport Also known as convective transport, bulk flow or filtration. Important in the absorption of low mol. Wt. (less than 100). Low molecular size (smaller than the diameter of the pore) & generally water-soluble drugs through narrow, aqueous filled channels or pores in the membrane structure. e.g. urea, water & sugars. The driving force for the passage of the drugs is the hydrostatic or the osmotic pressure difference across the membrane. 08/10/2010 KLECOP, Nipani

dc = rate of the absorption. dt N = number of pores The rate of absorption via pore transport depends on the number & size of the pores, & given as follows: dc = N. R2. A . ∆C dt (η) (h) where, dc = rate of the absorption. dt N = number of pores R = radius of pores ∆C = concentration gradient η = viscosity of fluid in the pores 08/10/2010 KLECOP, Nipani

CARRIER MEDIATED TRANSPORT MECHANISM Involves a carrier (a component of the membrane) which binds reversibly with the solute molecules to be transported to yield the carrier solute complex which transverses across the membrane to the other side where it dissociates to yield the solute molecule The carrier then returns to its original site to accept a fresh molecule of solute. There are two types of carrier mediated transport system: a) facilitated diffusion b) active transport 08/10/2010 KLECOP, Nipani

a) Facilitated diffusion This mechanism involves the driving force is concentration gradient. In this system, no expenditure of energy is involved (down-hill transport), therefore the process is not inhibited by metabolic poisons that interfere with energy production. 08/10/2010 KLECOP, Nipani

Limited importance in the absorption of drugs. e.g. Such a transport system include entry of glucose into RBCs & intestinal absorption of vitamins B1 & B2. A classical example of passive facilitated diffusion is the gastro-intestinal absorption of vitamin B12. An intrinsic factor (IF), a glycoprotein produced by the gastric parietal cells, forms a complex with vitamin B12 which is then transported across the intestinal membrane by a carrier system. 08/10/2010 KLECOP, Nipani

b) Active transport More important process than facilitated diffusion. The driving force is against the concentration gradient or uphill transport. Since the process is uphill, energy is required in the work done by the barrier. As the process requires expenditure of energy, it can be inhibited by metabolic poisons that interfere with energy production. 08/10/2010 KLECOP, Nipani

If drugs (especially used in cancer) have structural similarities to such agents, they are absorbed actively. A good example of competitive inhibition of drug absorption via active transport is the impaired absorption of levodopa when ingested with meals rich in proteins. The rate of absorption by active transport can be determined by applying the equation used for Michalies-menten kinetics: dc = [C].(dc/dt)max dt Km + [C] Where, (dc/dt)max = maximal rate of drug absorption at high drug concentration. [C] = concentration of drug available for absorption Km = affinity constant of drug for the barrier. 08/10/2010 KLECOP, Nipani

IONIC OR ELECTROCHEMICAL DIFFUSION This charge influences the permeation of drugs. Molecular forms of solutes are unaffected by the membrane charge & permeate faster than ionic forms. The permeation of anions & cations is also influenced by pH. Thus, at a given pH, the rate of permeation may be as follows: Unionized molecule > anions > cations 08/10/2010 KLECOP, Nipani

The permeation of ionized drugs, particularly the cationic drugs, depend on the potential difference or electrical gradient as the driving force across the membrane. Once inside the membrane, the cations are attached to negatively charged intracellular membrane, thus giving rise to an electrical gradient. If the same drug is moving from a higher to lower concentration, i.e., moving down the electrical gradient , the phenomenon is known as electrochemical diffusion. 08/10/2010 KLECOP, Nipani

ION PAIR TRANSPORT It is another mechanism is able to explain the absorption of such drugs which ionize at all pH condition. 08/10/2010 KLECOP, Nipani

This phenomenon is known as ion-pair transport. Transport of charged molecules due to the formation of a neutral complex with another charged molecule carrying an opposite charge. Drugs have low o/w partition coefficient values, yet these penetrate the membrane by forming reversible neutral complexes with endogenous ions. e.g. mucin of GIT. Such neutral complexes have both the required lipophilicity as well as aqueous solubility for passive diffusion. This phenomenon is known as ion-pair transport. 08/10/2010 KLECOP, Nipani

ENDOCYTOSIS It involves engulfing extracellular materials within a segment of the cell membrane to form a saccule or a vesicle (hence also called as corpuscular or vesicular transport) which is then pinched off intracellularly. 08/10/2010 KLECOP, Nipani

In endocytosis, there are three process: A) Phagocytosis B) Pinocytosis C) Transcytosis 08/10/2010 KLECOP, Nipani

A) Phagocytosis 08/10/2010 KLECOP, Nipani

B) Pinocytosis This process is important in the absorption of oil soluble vitamins & in the uptake of nutrients. 08/10/2010 KLECOP, Nipani

C) Transcytosis It is a phenomenon in which endocytic vesicle is transferred from one extracellular compartment to another. 08/10/2010 KLECOP, Nipani

Diagram Representing Absorption, Distribution, Metabolism and Excretion The ultimate goal is to have the drug reach the site of action in a concentration which produces a pharmacological effect. No matter how the drug is given (other than IV) it must pass through a number of biological membranes before it reaches the site of action. 08/10/2010 KLECOP, Nipani

DIFFUSION THROUGH MEMBRANES Rate dependent on polarity and size. Polarity estimated using the partition coefficient. The greater the lipid solubility – the faster the rate of diffusion Smaller molecules (nm/A0) penetrate more rapidly. Highly permeable to O2, CO2, NO and H2O . Large polar molecules – sugar, aa, phosphorylated intermediates – poor permeability These are essential for cell function – must be actively transported 08/10/2010 KLECOP, Nipani

MOVEMENT OF SUBSTANCES ACROSS CELL MEMBRANES 08/10/2010 KLECOP, Nipani

BIOLOGICAL FACTORS: Penetration Of Drugs Through Gastro-intestinal Tract Penetration Of Drugs Through Blood Brain Barrier Penetration Of Drugs Through Placental Barrier Penetration Of Drugs Through Across The Skin Penetration Of Drugs Through The Mucous Membrane Of The Nose, Throat, Trachea, Buccal Cavity, Lungs ,Vaginal And Rectal Surfaces PHYSIOLOGICAL FACTORS: Gastrointestinal (Gi) Physiology Influence Of Drug Pka And Gi Ph On Drug Absorbtion Git Blood Flow Gastric Emptying Disease States 08/10/2010 KLECOP, Nipani

PENETRATION OF DRUGS THROUGH GASTRO-INTESTINAL TRACT The Git barrier that separates the lumen of the stomach and intestine from systemic circulation and is composed of lipids, proteins and polysaccharides. Git mucosa is a semi permeable membrane across which various nutrients like Carbohydrates, Amino acids, Vitamins and foreign substances are transported and absorbed into the blood by various mechanisms like: 1. Passive diffusion 2. Pore transport 3. Facilitated transport 4. Active transport 5. Pinocytosis 08/10/2010 KLECOP, Nipani

1. PASSIVE DIFFUSION Major process for absorption of more than 90% of drugs Diffusion follows Fick’s law: The drug molecules diffuse from a region of higher concentration to a region of lower concentration till equilibrium is attained. Rate of diffusion is directly proportional to the concentration gradient across the membrane. Factors affecting Passive diffusion: Diffusion coefficient of the drug Related to lipid solubility and molecular wt. Thickness and surface area of the membrane Size of the molecule 08/10/2010 KLECOP, Nipani

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2. PORE TRANSPORT It involves the passage of ions through Aq. Pores (4-40 A0) Low molecular weight molecules (less than 100 Daltons) eg- urea, water, sugar are absorbed. Also imp. In renal excretion, removal of drug from CSF and entry of drugs into liver. 08/10/2010 KLECOP, Nipani

3. FACILITATED DIFFUSION Carrier mediated transport (downhill transport) Faster than passive diffusion No energy expenditure is involved Not inhibited by metabolic poisons Important in transport of Polar molecules and charged ions that dissolve in water but they can not diffuse freely across cell membranes due to the hydrophobic nature of the phospholipids. Eg. 1. entry of glucose into RBCs 2. intestinal absorption vitamin B1 ,B2 3. transport of amino acids thru permeases 08/10/2010 KLECOP, Nipani

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4. ACTIVE TRANSPORT Carrier mediated transport (uphill transport) Energy is required in the work done by the carrier Inhibited by metabolic poisons Endogenous substances that are transported actively include sodium, potassium, calcium, iron, glucose, amino acids and vitamins like niacin, pyridoxin. Drugs having structural similarity to such agents are absorbed actively Eg. 1. Pyrimidine transport system – absorption of 5 FU and 5 BU 2. L-amino acid transport system – absorption of methyldopa and levodopa 08/10/2010 KLECOP, Nipani

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5. PINOCYTOSIS Uptake of fluid solute. Pinocytosis ("cell-drinking") Uptake of fluid solute. A form of endocytosis in which small particles are brought into the cell in the form of small vesicles which subsequently fuse with lysosomes to hydrolyze, or to break down, the particles. This process requires energy in the form of (ATP). Polio vaccine and large protein molecules are absorbed by pinocytosis 08/10/2010 KLECOP, Nipani

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PENETRATION OF DRUGS THROUGH BLOOD BRAIN BARRIER A stealth of endothelial cells lining the capillaries. It has tight junctions and lack large intra cellular pores. Further, neural tissue covers the capillaries. Together , they constitute the so called BLOOD BRAIN BARRIER Astrocytes : Special cells / elements of supporting tissue found at the base of endothelial membrane. The blood-brain barrier (BBB) is a separation of circulating blood and cerebrospinal fluid (CSF) maintained by the choroid plexus in the central nervous system (CNS). 08/10/2010 KLECOP, Nipani

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Various approaches to promote crossing the BBB by drugs: Since BBB is a lipoidal barrier, It allows only the drugs having high o/w partition coefficient to diffuse passively where as moderately lipid soluble and partially ionised molecules penetrate at a slow rate. Endothelial cells restrict the diffusion of microscopic objects (e.g. bacteria ) and large or hydrophillic molecules into the CSF, while allowing the diffusion of small hydrophobic molecules (O2, hormones, CO2). Cells of the barrier actively transport metabolic products such as glucose across the barrier with specific proteins. Various approaches to promote crossing the BBB by drugs: Use of Permeation enhancers such as dimethyl sulfoxide (DMSO) Osmotic disruption of the BBB by infusing internal carotid artery with mannitol Use of Dihydropyridine redox system as drug carriers to the brain ( the lipid soluble dihydropyridine is linked as a carrier to the polar drug to form a prodrug that rapidly crosses the BBB ) 08/10/2010 KLECOP, Nipani

PENETRATION OF DRUGS THROUGH PLACENTAL BARRIER Placenta is the membrane separating fetal blood from the maternal blood. It is made up of fetal trophoblast basement membrane and the endothelium. Mean thickness (25 µ) in early pregnancy and reduces to (2 µ) at full term Many drugs having mol. wt. < 1000 daltons and moderate to high lipid solubility e.g. ethanol, sulfonamides , barbiturates, steroids , anticonvulsants and some antibiotics cross the barrier by simple diffusion quite rapidly . Nutrients essential for fetal growth are transported by carrier mediated processes 08/10/2010 KLECOP, Nipani

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PENETRATION OF DRUGS THROUGH ACROSS THE SKIN Skin is composed of three primary layers: the epidermis , which provides waterproofing and serves as a barrier to infection; the dermis , which serves as a location for the appendages of skin; and the hypodermis (subcutaneous adipose layer). The stratum corneum is the outermost layer of the epidermis and is composed mainly of dead keratinised cells (from lack of oxygen and nutrients). It has a thickness between 10 - 40 μm. The dermis is the layer of skin beneath the epidermis. It contains the hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels. Hypodermis - Its purpose is to attach the skin to underlying bone and muscle as well as supplying it with blood vessels and nerves. The main cell types are fibroblasts, macrophages and adipocytes (the hypodermis contains 50% of body fat). 08/10/2010 KLECOP, Nipani

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FACTORS IN SKIN PERMEATION ROUTES OF PENETRATION Through follicular region Through sweat ducts Through unbroken stratum corneum FACTORS IN SKIN PERMEATION Thickness of the skin layer: (Thickest on palms and soles & thinest on the face) Skin condition: permeability of skin is affected by age, disease state or injury. Skin temp.: permeability increases with increase in temp. Hydration state APPROACHES TO ENHANCE SKIN PERMEATION Innuction Iontophoresis Sonophoresis Magnetophoresis 08/10/2010 KLECOP, Nipani

Penetration Of Drugs Through The Mucous Membrane Of The Nose, Throat, Trachea, Buccal Cavity, Lungs ,Vaginal And Rectal Surfaces The barrier for the drug absorption is the capillary endothelial membrane which is lipoidal and consists of pores . Thus, lipid soluble drugs can easily penetrate by diffusion and smaller drug molecules can penetrate by pore transport. 08/10/2010 KLECOP, Nipani

Gastrointestinal (GI) Physiology Membrane Blood Supply Surface Area Transit Time By-pass liver BUCCAL approx 6 thin Good, fast absorption with low dose small Short unless controlled yes ESOPHAGUS 6 Very thick, no absorption - short STOMACH 1 – 3 Normal Lipophilic,acidic and neutral drugs good 30 - 40 minutes, reduced absorption no DUODENUM 5 – 7 Mainly lipohilic and neutral drugs large very short (6" long) SMALL INTESTINE 6 -7 All types of drugs very large 10 - 14 ft, 80 cm 2 /cm about 3 hours LARGE INTESTINE 6.8 - 7 not very large 4 - 5 ft long, up to 24 hr lower colon, rectum yes 08/10/2010 KLECOP, Nipani

SMALL INTESTINE : Major site for absorption of most drugs due to its large surface area (0.33 m2 ). It is 7 meters in length and is approximately 2.5-3 cm in diameter. The Folds in small intestine called as folds of kerckring, result in 3 fold increase in surface area ( 1 m2). These folds possess finger like projections called Villi which increase the surface area 30 times ( 10 m2). From the surface of villi protrude several microvilli which increase the surface area 600 times ( 200 m2). Blood flow is 6-10 times that of stomach. PH Range is 5–7.5 , favourable for most drugs to remain unionised. Peristaltic movement is slow, while transit time is long. Permeability is high. All these factors make intestine the best site for absorbtion of most drugs. 08/10/2010 KLECOP, Nipani

INFLUENCE OF DRUG pKa AND GI PH ON DRUG ABSORBTION Drugs Site of absorption Very weak acids (pKa > 8.0) Unionized at all ph values Absorbed along entire length of GIT Moderately weak acids (pKa 2.5 – 7.5) Unionized in gastric ph Ionized in intestinal ph Better absorbed from stomach Strong acids (pKa <2.5) Ionized at all ph values Poorly absorbed from git Very weak bases (pKa < 5) Moderately weak bases (pKa 5 – 11 ) Ionized in gastric ph Unionized in intestinal ph Better absorbed from intestine Strong bases (pKa >11) Poorly Absorbed from GIT 08/10/2010 KLECOP, Nipani

GIT BLOOD FLOW It plays an imp. role in drug absorption by continuously maintaining the conc. Gradient across the epithelial membrane Polar molecules that are slowly absorbed show no dependence on blood flow The absorption of lipid soluble drugs and molecules that are small enough to easily penetrate through Aq. pores is rapid and highly dependent on rate of blood flow 08/10/2010 KLECOP, Nipani

GASTRIC EMPTYING The process by which food leaves the stomach and enters the duodenum. It is a RDS in drug absorbtion. Rapid Gastric Emptying Advisable when : Rapid onset of action is desired eg. Sedatives Dissolution occurs in the intestine eg. Enteric coated tablets Drugs not stable in gi fluids eg. penicillin G Drug is best absorbed from small intestine eg. Vitamin B12 Delay in Gastric Emptying recommended when Food promotes drug dissolution and absorbtion eg. Gresiofulvin Disintegration and dissolution is is promoted by gastric fluids 08/10/2010 KLECOP, Nipani

Factors affecting Gastric Emptying Volume of Ingested Material As volume increases initially an increase then a decrease. Bulky material tends to empty more slowly than liquids Type of Meal Gastric emptying rate: carbohydrates > proteins > fats Temperature of Food Increase in temperature, increase in emptying rate Body Position Lying on the left side decreases emptying rate and right side promotes it Git PH Retarded at low stomach PH and promoted at higher alkaline PH Emotional state Anxiety promotes where as depression retards it Disease states gastric ulcer, hypothyroidism retards it, while duodenal ulcer, hyperthyroidism promotes it. 08/10/2010 KLECOP, Nipani

DISEASE STATES CHF decreases blood flow to the Git, alters GI PH, secretions and microbial flora. Cirrhosis influences bioavailability mainly of drugs that undergo considerable 1st pass metabolism eg. Propranolol Git infections like cholera and food poisoning also result in malabsorbtion. 08/10/2010 KLECOP, Nipani

PHYSIO-CHEMICAL FACTORS PHYSICAL FACTORS PHYSIO-CHEMICAL FACTORS 08/10/2010 KLECOP, Nipani

PHYSICAL FACTORS PARTICLE SIZE Smaller particle size, greater surface area then higher will be dissolution rate, because dissolution is thought to take place at the surface area of the solute( Drug). This study is imp. for drugs that have low aqueous solubility. Absorption of such drugs can be increased by increasing particle size by Micronization. ex. Griseofulvin, active intravenously but not effective when given orally. 08/10/2010 KLECOP, Nipani

ex. Bioavailability of Phenacetin is increased by tween 80. To poor soluble drug, disintegration agents and surface active agents may be added . ex. Bioavailability of Phenacetin is increased by tween 80. Micronization also reduces the dose of some drugs ex. the dose of griseofulvin is reduced to one half while the dose of spironolactone is reduced to one twentieth. PARTICLE SIZE 08/10/2010 KLECOP, Nipani

Lesser particle size is always not helpful Ex. Micronization of Aspirin, phenobarbital, lesser effective surface area and hence lesser dissolution rate Reasons: On their surface, hydrophobic drugs absorb air and reduce their wettability Particle having size below 0.1 micron reaggregate to form large particle Particle having certain micro size get electrical charge which preventing contact with wetting medium 08/10/2010 KLECOP, Nipani

Ex. of such drugs are Penicillin G & Erythromycin Finally drug size reduction and subsequent increase in surface area and dissolution rate is always not useful. Ex. of such drugs are Penicillin G & Erythromycin These Drugs are unstable and degrade quickly in solution. Sometime, reduction in particle size of nitrofurantoin and piroxicam increase gastric irritation These problem can be overcome by Microencapsulation. 08/10/2010 KLECOP, Nipani

2. Crystal Form Substance can exist either in a crystalline or amorphous form. When substance exist in more than one crystalline form, the different form are called polymorphs and the phenomena as polymorphism . Two types of Polymorphism 1) Enantiotropic polymorph ex. Sulfur 2) Monotropic polymorph ex. Glyceryl Stearates Polymorphs have the same chemical structure but different physical properties such as solubility, density, hardness etc. ex. Chlormphenicol has a several crystal form, and when given orally as a suspension, the drug concentration in the body was found to be dependent on the percentage of β - polymorph in the suspension. The form is more soluble and better absorbed. 08/10/2010 KLECOP, Nipani

About 40% of all organic compounds exhibit polymorphism. One of the several form of polymorphic forms is more stable than other. Such a stable form having low energy state and high melting point and least aqueous solubility The remaining polymorphs are called as metastable forms which have high energy state, low melting point and high aqueous solubilities. About 40% of all organic compounds exhibit polymorphism. Some drug exists in amorphous form which have no internal crystal structure. Such drugs have high energy states than crystal form hence they have greater aqueous solubility than crystalline form. Ex. Novobiocin, cortisone acetate. 08/10/2010 KLECOP, Nipani

Many drugs associate with solvent and forms solvates 3. Solvates And Hydrates Many drugs associate with solvent and forms solvates Solvent is water then it is called as hydrate eg. Anhydrous form of caffeine and theophylline dissolve more rapidly than hydrous form of these drugs. Solvate form of drugs with org. solvent may dissolve fast in water than non solvated form. eg. Fluorocortisone 4. Complexation This property can influence the effective drug concentration in gi fluids. Complexation of drug and gi fluids may alter the rate and extent of absorption eg. Intestinal Mucin form complex with Streptomycin and Dihydro Streptomycin. In some cases, Poor water soluble drugs can be administered as water soluble complexes. eg. Hydroquinone with Digoxin. 08/10/2010 KLECOP, Nipani

6.Drug Stability And Hydrolysis In GIT 5.Adsorption It is a physical and surface phenomena where the drug molecules are held on the surface of some inert substances by vanderwall’s forces. ex. Charcoal used as an antidote; When it is co-administered with promazine, then it reduces the rate and extent of absorption Cholestyramine reduces the absorption of warfarin. 6.Drug Stability And Hydrolysis In GIT Drugs undergoes various reactions due to wide spectrum of ph and enzymatic activity of GI fluid namely acid and enzymatic hydrolysis. eg. T½ of Penicillin G= 1 min. at pH 1 T½ of Penicillin G= 9 min. at pH2 So it means Penicillin G is stable at less acidic pH Erythromycin and its esters are unstable at gastric fluid (T½=Less than 2 min.) 08/10/2010 KLECOP, Nipani

8. Presence Of Surfactant 7. Salts Na or K salts of weak acid dissolves rapidly than free acid. ex. Na salts of Novobiocin shows improved bioavailability ex. Al salts of weak acid and pamoate salt of weak base Certain salts also may have low solubility and dissolution rate. 8. Presence Of Surfactant Use of wetting agent and Solubilizing agent improve the Dissolution rate & absorption of drugs. Ex. Tween 80 increase the rate & extent of absorption of Phenacetin. 9. Dissolution Disintegration is the formation of dispersed granules from an intact solid dosage form whereas the dissolution is the formation of solvated drug molecules from the drug 08/10/2010 KLECOP, Nipani

DRUG IN SYSTEMIC CIRCULATION SOLID DRUG DISSOLUTION DRUG AT ABSORPTION SITE ABSORPTION DRUG IN SYSTEMIC CIRCULATION 08/10/2010 KLECOP, Nipani

NOYES AND WHITNEY’S EQUATION dc/dt = KS(CS-C) Where, dc/dt = Rate constant, K = constant, S = surface area of the dissolving solid, Cs=solubility of the drug in the solvent, C=concentration of drug in the solvent at time t. Constant K=D/h Where, D is the diffusion coefficient of the dissolving material and h is the thickness of the diffusion layer Here, C will always negligible compared to Cs So, dc/dt=DSCs/h 08/10/2010 KLECOP, Nipani

PHYSICOCHEMICAL FACTORS 1) pH PARTITION THEORY (Brodie) : It explain drug absorption from GIT and its distribution across biomembranes. Drug(>100 daltons) transported by passive diffusion depend upon: dissociation constant, pKa of the drug lipid solubility, K o/w pH at absorption site. Most drugs are either weak acids or weak bases whose degree of ionization is depend upon pH of biological fluid. 08/10/2010 KLECOP, Nipani

The fraction of drug remaining unionized is a function of both For a drug to be absorbed, it should be unionized and the unionized portion should be lipid soluble. The fraction of drug remaining unionized is a function of both Dissociation constant (pKa) and pH of solution. The pH partition theory is based on following assumption: GIT acts as a lipoidal barrier to the transport of the drug The rate of absorption of drug is directly proportional to its fraction of unionised drug Higher the lipophilicity of the unionised degree, better the absorption. 08/10/2010 KLECOP, Nipani

HENDERSON HASSELBATCH EQUATION For acid, pKa - pH = log[ Cu/Ci ] For base, pKa – pH = log[ Ci/Cu ] Eg. Weak acid aspirin (pKa=3.5) in stomach (pH=1) will have > 99%of unionized form so gets absorbed in stomach Weak base quinine (pKa=8.5) will have very negligible unionization in gastric pH so negligible absorption Several prodrugs have been developed which are lipid soluble to overcome poor oral absorption of their parent compounds. 08/10/2010 KLECOP, Nipani

eg. Pivampicilin, the pivaloyloxy-methyl ester of ampicilin is More lipid soluble than ampicilin. Lipid solubility is provided to a drug by its partition coefficient between An organic solvent and water or an aq. Buffer (same pH of ab. Site) E.g. Barbital has a p.c. of 0.7 its absorption is 12% Phenobarbital ( p.c = 4.8 absorption=12%) Secobarbital (p.c =50.7 absorption=40%) 08/10/2010 KLECOP, Nipani

2)DRUG SOLUBILITY The absorption of drug requires that molecule be in solution at absorption site. Dissolution, an important step, depends upon solubility of drug substance. pH solubility profile: pH environment of GIT varies from Acidic in stomach to slightly Alkaline in a small intestine. soluble 1)Basic drug 1) Acidic medium( stomach) 2)Acidic drug 2) basic medium( intestestine) 08/10/2010 KLECOP, Nipani

Improvement of solubility: Addition of acidic or basic excipient Ex: Solubility of Aspirin (weak acid) increased by addition of basic excipient. For formulation of CRD , buffering agents may be added to slow or modify the release rate of a fast dissolving drug. 08/10/2010 KLECOP, Nipani

PHARMACEUTICAL FACTORS MEANS Absorption rate depends on the dosage Form which is administred,ingredients used, procedures Used in formulation of dosage forms. The availability of the drug for absorption from the dosage forms is in order. Solutions > Suspensions > capsules > Compressed Tablets > Coated tablets. 08/10/2010 KLECOP, Nipani

SOLUTIONS Shows maximum bioavailability and factors affecting Absorption from solution are as follows Chemical stability of drug Complexation: between drug and exipients of formulation to increase the solubility, stability. 3. Solubilization: incorporation of drug into micelles to increase the solubility of drugs. 4. Viscosity 5. Type of solution: Whether aqueous or oily solution. 08/10/2010 KLECOP, Nipani

It comes next after solutions with respect to bioavailability SUSPENSIONS: It comes next after solutions with respect to bioavailability Factors that affects absorption from suspensions are Particle size and effective surface area of dispersed phase 2. Crystal form of drug: some drug can change their crystal structure. Eg. Sulfathiazole can change its polymorphic form, it can be overcome by addition by adding PVP. 3. Complexation: Formation of nonabsorbable complex between drug and other ingredients. Eg. Promazine forms a complex with attapulgite. 08/10/2010 KLECOP, Nipani

4. Inclusion of surfactant Eg. The absorption of phenacitin from suspension is increased in presence of tween 80. 5. Viscosity of suspension Eg. Methyl cellulose reduces the rate and absorption of nitrofurantoin 6. Inclusion of colourants: Eg. Brilliant blue in phenobarbitone suspension. 08/10/2010 KLECOP, Nipani

CAPSULES Two types of capsule Hard gelatin capsule 2. Soft gelatin capsule 08/10/2010 KLECOP, Nipani

The rate of absorption of drugs from capsule is function HARD GELATIN CAPSULE The rate of absorption of drugs from capsule is function Of some factors. 1.Dissolution rate of gelatin shell. 2.The rate of penetration of GI fluids into encapsulated mass 3.The rate at which the mass disaggregates in the GI fluid 4. The rate of dissolution. 5. Effect of excipients; a).Diluents b).Lubricants c). Wetting characteristics of drug d).Packing density 08/10/2010 KLECOP, Nipani

SGS has a gelatin shell thicker than HGS,but shell is SOFT GELATIN CAPSULE SGS has a gelatin shell thicker than HGS,but shell is Plasticized by adding glycerin,sorbitol.SGS may used To contain non aqueous solution or liquid or semi solid. SGC have a better bioavailability than powder filled HGC And are equivalent to emulsions. Eg. Quinine derivative was better absorbed from SGC Containing drug base compared with HGC containing HCl salts. Grieseoflavin exhibited 88% absorption from soft gelatin Capsules compared to HGC(30%) 08/10/2010 KLECOP, Nipani

TABLETS 1.Compressed tablets 2. Coated tablets 08/10/2010 KLECOP, Nipani

Bioavailability are more due to large reduction in surface area. Compressed tablets Bioavailability are more due to large reduction in surface area. A B Intact tablets a granules primary drug particles K2 K1 K3 Drug in GI fluid K4 Drug absorbed in body 08/10/2010 KLECOP, Nipani

The rate constants decrease in the following order. K3>>K2>>K1 The overall dissolution rate and bioavailability of a poor Soluble drugs is influenced by 1.The physicochemical properties of liberated particles. 2. The nature and quantity of additives. 3. The compaction pressure and speed of compression. 4. The storage and age of tablet 08/10/2010 KLECOP, Nipani

Na Salicylates + starch = Faster dissolution 1.Effect of diluents : Na Salicylates + starch = Faster dissolution Na salicylates + lactose=Poor dissolution. 2.Effect of Granulating agent: Phenobarbital + Gelatin solution=Faster dissolution Phenobarbital+PEG 6000= poor dissolution. 3.Effect of lubricants: Magnesium stearate will retard the dissolution of aspirin tablet Whereas SLS enhance the dissolution. 08/10/2010 KLECOP, Nipani

4.Effect of disintegrants: Starch tend to swell with wetting and break apart the dosage form. It is reported that 325mg of salicylic acid tablet were prepared by using different concentrations (5%,10%,20%) and max. dissolution was achieved With 20% starch. 5. Effect of colorants: 6.Effect of Compression force: 08/10/2010 KLECOP, Nipani

There are three types of coating Sugar coating Film coating COATED TABLETS: There are three types of coating Sugar coating Film coating Enteric coating SUGAR COATING: Sugar,Shellac,fatty glycerides, bees wax, silicone resin Sub coating agent: Talc,acacia,starch. FILM COATING: Polymers, dispersible cellulose derivatives like HPMC CMC. ENTERIC COATING: Shellac, cellulose acetate phthalate etc. 08/10/2010 KLECOP, Nipani

Factors affecting the drug release are 1.Thickness of coating e.g.. Quinine shows decrease in rate of absorption if coated with cellulose acetate phthalate. 2.The amount of dusting powder: 3.Effect of ageing: e.g. The shellac coated tablets of Para amino salicylic acid when given after two years plasma concentration of 6-7mg/100ml. However the tablets stored for 3½ years showed plasma concentration of only 2mg/100ml which is the sub therapeutic effect. 08/10/2010 KLECOP, Nipani

SUBLINGUAL / BUCCAL ROUTE SUBLINGUAL ROUTE: the dosage form is placed beneath the tongue. BUCCAL ROUTE: Dosage form is placed between the cheek and teeth or In the cheek pouch. Drugs administered by this route are supposed to produce systemic drug effects, and consequently, they must have good absorption from oral mucosa. Oral mucosal regions are highly vascularised therefore rapid onset of action is observed. For Eg, anti-anginal drug Nitroglycerin. 08/10/2010 KLECOP, Nipani

SUBLINGUAL / BUCCAL ROUTE Blood perfuses oral regions drains directly into the general circulation. Barrier to drug absorption from these routes is epithelium of oral mucosa. Passive diffusion is the major mechanism of absorption of most drugs. In general, sublingual tablets are designed to dissolve slowly to minimize possibility of swallowing the dose. Exception include: Nitroglycerin, Isosorbide dinitrate tablets which dissolves within minutes in buccal cavity to provide prompt treatment of acute anginal episodes. 08/10/2010 KLECOP, Nipani

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Factors to be considered: Lipophilicity of drug: The lipid solubility should be high for absorption. Salivary secretion: drug should be soluble in buccal fluid. pH of saliva: pH of saliva is usually 6. Storage compartment: some drugs have storage compartment in buccal mucosa. Eg, Buprenorphine Thickness of oral epithelium: Sublingual absorption is faster than buccal, because former region is thinner than that of buccal mucosa. 08/10/2010 KLECOP, Nipani

FACTORS LIMITTING DRUG ADMINISTRATION: Limited mucosal surface area. Taste of medicament and discomfort. EXAMPLES: Nitroglycerin, Isosorbide dinitrate, Progesterone, Oxytocin, Fenosterol, Morphine. 08/10/2010 KLECOP, Nipani

RECTAL ADMINISTRATION: Absorption across the rectal mucosa occurs by passive diffusion. This route of administration is useful in children, old people and unconscious patients. Eg., drugs that administered are: aspirin, acetaminophen, theophylline, indomethacin, promethazine & certain barbiturates. 08/10/2010 KLECOP, Nipani

PARENTERAL ROUTES: . 08/10/2010 KLECOP, Nipani

INTRAVENOUS ROUTE: INTRAVENOUS ROUTE: Absorption phase is bypassed (100% bioavailability) 1.Precise, accurate and almost immediate onset of action, 2. Large quantities can be given, fairly pain free 3. Greater risk of adverse effects a. High concentration attained rapidly b. Risk of embolism 08/10/2010 KLECOP, Nipani

INTRAVENOUS ROUTE: This route is used when a rapid clinical response is required like treatment of epileptic seizures, acute asthmatic and cardiac arrhythmias. There may also be a danger of precipitation of drug in the vein if the inj. is too rapidly. This could result in thrombophlebitis. This mode of administration is required with drugs having short half lives and narrow therapeutic index. Bioavailability is not considered by this route. Mainly antibiotics are administered by this route. 08/10/2010 KLECOP, Nipani

Intra arterial injection In this route the drugs are injected directly into the artery. It is mainly used for cancer chemotherapy. It increased drug delivery to the area supplied by the infused artery and decreased drug delivery to systemic circulation. 08/10/2010 KLECOP, Nipani

INTRA MUSCULAR INJECTION Absorption of drug from muscles is rapid and absorption rate is perfusion rate limited. Polypeptides of less than approx 5000 gram per mole primarily pass through capillary pathway Greater than about 20000 g/mol are less able to traverse capillary wall, they primarily enter blood via lymphatic pathway. 08/10/2010 KLECOP, Nipani

Factors determining rate of drug absorption: 1. Vascularity to the inj. Site: Blood flow rates to intramuscular tissues are: Arm (deltoid) > thigh (vastus lateralis) > buttocks (gluteus maximus). 2. Lipid solubility and ionisation of drug. 3. Molecular size of drug. 4. Volume of inj. And drug concentration. 5. pH & viscosity of inj. vehicle. 08/10/2010 KLECOP, Nipani

1. Slow and constant absorption SUBCUTANOUS ROUTE: 1. Slow and constant absorption 2. Absorption is limited by blood flow, affected if circulatory problems exist. 3. The blood supply to this is poorer than that of muscular tissue. 4. Concurrent administration of vasoconstrictor will slow absorption, e.g. Epinephrine. 5. The absorption is hastened by massage, application of heat to increase blood flow and inclusion of enzyme Hyaluronidase in drug solution. eg. Insulin. 08/10/2010 KLECOP, Nipani

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TOPICAL ADMINISTRATION: MUCOSAL MEMBRANES(eye drops, antiseptic, sunscreen, nasal, etc.) SKIN a. Dermal - rubbing in of oil or ointment (local action) b. Transdermal - absorption of drug through skin (systemic action) i. stable blood levels ii. no first pass metabolism iii. drug must be potent. 08/10/2010 KLECOP, Nipani

Skin consist of three layers : Epidermis Dermis Subcutaneous fat tissue The main route for the penetration of the drugs is generally through epidermal layer Stratum corneum is the rate limiting barrier in passive percutaneous absorption of drug. 08/10/2010 KLECOP, Nipani

The stratum corneum is the outermost layer of the epidermis and is composed mainly of dead keratinized cells (from lack of oxygen and nutrients). It has a thickness between 10 - 40 μm. The dermis is the layer of skin beneath the epidermis. It contains the hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels. Hypodermis - Its purpose is to attach the skin to underlying bone and muscle as well as supplying it with blood vessels and nerves. The main cell types are fibroblasts, macrophages and adiposities (the hypodermis contains 50% of body fat). 08/10/2010 KLECOP, Nipani

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OCULAR ADMINISTRATION Eye is the most easily accessible site for topical administration of a medication. Topical application of drug to eyes meant for : Mydriasis, miosis, anaesthesia, treatment of infection, glaucoma etc. Opthalmic solution are administered into cul-de-sac. Barrier to intra occular penetration is cornea. It possess both hydrophilic and lipophilic characterstics. pH of lacrimal fluid is 7.4. pH of lacrimal fluid influences absorption of weak electrolyte like Pilocarpine. 08/10/2010 KLECOP, Nipani

OCULAR ADMINISTRATION High pH of formulation: decrease tear flow and Low pH of formulation: increases tear flow. Human eye can hold around 10 microlitre of fluid. So small volume in concentrated form increases effectiveness. Viscosity empartners increases bioavailability eg, oily solutions, ointment etc. Systemic entry of drug occur by lacrimal duct which drains lacrimal fluid into nasal cavity. 08/10/2010 KLECOP, Nipani

Composition of eye Water - 98% Solid -1.8% Organic element – Protein - 0.67%, sugar - 0.65%, Nacl - 0.66% Other mineral element sodium, potassium and ammonia - 0.79% 08/10/2010 KLECOP, Nipani

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Characteristics required to optimize ocular drug delivery system Good corneal penetration. Prolong contact time with corneal tissue. Simplicity of instillation for the patient. Non irritative and comfortable form (viscous solution should not provoke lachrymal secretion and  reflex blinking) Appropriate rheological properties concentrations of the viscous system. 08/10/2010 KLECOP, Nipani

Advantages Increase ocular residence….. Improving bioavailability Prolonged drug release….. better efficacy Less visual & systemic side effects Increased shelf life Exclusion of preservatives Reduction of systemic side effects Reduction of the number of administration Better patient compliance Accurate dose in the eye…. a better therapy 08/10/2010 KLECOP, Nipani

FACTOR INFLUENCING PERCUTANEOUS ABSORPTION Drug release from dosage form Drug concentration in the formulation Drug oil water partition coefficient. Drug affinity to the skin tissue Surface area Site of application Hydration of skin Nature of vehicle used 08/10/2010 KLECOP, Nipani

FACTOR INFLUENCING PERCUTANEOUS ABSORPTION 9. Rubbing 10. Contact period 11. Permeation enhancers 08/10/2010 KLECOP, Nipani

INHALATIONAL ROUTE: 1.Gaseous and volatile agents and aerosols. 2.Rapid onset of action due to rapid access to circulation a.Large surface area b.Thin membranes separates alveoli from circulation c.High blood flow Particles larger than 20 micron and the particles impact in the mouth and throat. Smaller than 0.5 micron and they aren't retained. 08/10/2010 KLECOP, Nipani

Intra nasal administration Drugs generally administered by intra nasal route for treatment of local condition such as perennial rhinitis, allergic rhinitis and nasal decongestion etc. Absorption of lipophilic drugs through nasal mucosa by passive diffusion and absorption of polar drugs by pore transport. Rate of absorption of lipophilic drugs depend on their molecular weight. Drugs with molecular weight less than 400 daltons exhibit higher rate of absorption. 08/10/2010 KLECOP, Nipani

cont… Drugs with molecular weight 1000 daltons show moderate rate of absorption. Presently nasal route is becoming popular for systemic delivery of peptide and proteins, this is because of high permeability of nasal mucosa with vasculature. 08/10/2010 KLECOP, Nipani

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Advantages Rapid drug absorption via highly-vascularized mucosa Rapid onset of action Ease of administration, non-invasive Avoidance of the gastrointestinal tract and first-pass metabolism Improved bioavailability Lower dose/reduced side effects Improved convenience and compliance Self-administration. 08/10/2010 KLECOP, Nipani

Disadvantages Nasal cavity provides smaller absorption surface area when compared to GIT. Relatively inconvenient to patients when compared to oral delivery since there is possibility of nasal irritation. The histological toxicity of absorption enhancers used in the nasal drug delivery system is not yet clearly established. 08/10/2010 KLECOP, Nipani

Enhancement in absorption Following approaches used for absorption enhancement :- Use of absorption enhancers Increase in residence time. Administration of drug in the form of microspheres. Use of physiological modifying agents 08/10/2010 KLECOP, Nipani

Enhancement in absorption Use of absorption enhancers:- Absorption enhancers work by increasing the rate at which the drug pass through the nasal mucosa. Various enhancers used are surfactants, bile salts, chelaters, fatty acid salts, phospholipids, cyclodextrins, glycols etc. 08/10/2010 KLECOP, Nipani

Various mechanisms involved in absorption enhancements are:- Increased drug solubility Decreased mucosal viscosity Decrease enzymatic degradation Increased Paracellular transport Increased transcellular transport 08/10/2010 KLECOP, Nipani

Various mechanisms involved in absorption enhancements are:- Increase in residence time:- By increasing the residence time the increase in the higher local drug concentration in the mucous lining of the nasal mucosa is obtained. Various mucoadhesive polymers like methylcellulose, carboxy methyl cellulose or polyarcylic acid are used for increasing the residence time. 08/10/2010 KLECOP, Nipani

Various mechanisms involved in absorption enhancements are:- Use of physiological modifying agents:- These agents are vasoactive agents and exert their action by increasing the nasal blood flow. The example of such agents are histamine, leukotrienene D4, prostaglandin E1 and β-adrenergic agents like isoprenaline and terbutaline. 08/10/2010 KLECOP, Nipani

Applications of nasal drug delivery Nasal delivery of organic based pharmaceuticals :- Various organic based pharmaceuticals have been investigated for nasal delivery which includes drug with extensive presystemic metabolism. E.g. Progesterone, Estradiol, Nitroglycerin, Propranolol, etc. 08/10/2010 KLECOP, Nipani

Applications of nasal drug delivery Nasal delivery of peptide based drugs :- Nasal delivery of peptides and proteins is depend on – The structure and size of the molecule. Nasal residence time Formulation variables (pH, viscosity) E.g. calcitonin, secretin, albumins, insulin, glucagon, etc. 08/10/2010 KLECOP, Nipani

PULMONARY ADMINISTRATION The drugs may be administered for local action of bronchioles or their systemic effects through absorption of lungs. Inhalation sprays and aerosols are used to deliver the drugs to the lungs. Larger surface area of alveoli, high permeability of alveolar epithelium for drug penetration, and a rich vasculature are responsible for rapid absorption of drugs by this route 08/10/2010 KLECOP, Nipani

PULMONARY ADMINISTRATION In general particles greater than 10mm are retained in the throat and upper airways whereas fine particles reach the pulmonary epithelium Drugs generally administered by this route are bronchodilators (e.g.. Salbutamol, isoproterenol), antiallergic (e.g.. Cromolym sodium), and antiinflammatory (e.g.. Betamethasone, dexamethasone). 08/10/2010 KLECOP, Nipani

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Advantages Smaller doses can be administered locally. Reduce the potential incidence of adverse systemic effect. It used when a drug is poorly absorbed orally, e.g. Na cromoglicate. It is used when drug is rapidly metabolized orally, e.g. isoprenaline 08/10/2010 KLECOP, Nipani

IN-VITRO METHODS Everted small intestine sac method. Everted sac modification. Circulation technique. Everted intestinal ring or slice technique. 08/10/2010 KLECOP, Nipani

Why in-vitro studies Because of economical & ethical limitations of in-vivo studies. Simple & provide valuable information. To assess the major factors involved in absorption. Predict the rate & extent of drug absorption. Procedures are of great value during screening of new drug candidates. Carried out outside the body. Used to assess permeability of drug using animal tissues. 08/10/2010 KLECOP, Nipani

Everted small intestine sac technique Isolation of rat intestine Inverting the intestine Filling the sac with drug free buffer solution Immersion of sac in Erlenmeyer flask containing drug buffer solution 08/10/2010 KLECOP, Nipani Contd…

After incubation, the serosal content is assayed for drug content Flask & its contents oxygenated & agitated at 37oC for specific period of time After incubation, the serosal content is assayed for drug content 08/10/2010 KLECOP, Nipani

Figure( reverted sac technique) Serosal side Mucosal side (intestinal segment before eversion) Serosal side Buffer solution Ligature Mucosal side 08/10/2010 (after eversion) KLECOP, Nipani

Advantages Prolongs the viability & integrity of the preparation after removal from the animal. Convenience & accuracy with respect to drug analysis. The epithelial cells of the mucosal surface are exposed directly to the oxygenated mucosal fluid. Difficulty in obtaining more than one sample per intestinal segment DISADVANTAGES 08/10/2010 KLECOP, Nipani

Everted sac modification Crane & Wilson modification. Essential features of simple sac methods are retained. Modification- the intestine is tied to a cannula. 08/10/2010 KLECOP, Nipani

Buffer solution with drug cannula Plain buffer Buffer solution with drug Water maintained at 37o C aerator 08/10/2010 KLECOP, Nipani (FIG: EVERTED SAC MODIFICATION)

Procedure Animal fasted for 20-24hrs Water is allowed ad libitum Animal killed with blow on head or anesthetized with ether or chloroform Entire small intestine is everted 08/10/2010 KLECOP, Nipani Contd….

Distal ends tied & proximal end is attached to cannula Segments of 5-15cm length are cut from specific region of the intestine Distal ends tied & proximal end is attached to cannula Segments suspended in 40-100ml of drug mucosal solution. About 1ml/5cm length of drug free buffer is then placed in serosal compartment Mucosal solution aerated 08/10/2010 KLECOP, Nipani

How to determine the rate of drug transfer The entire volume of serosal solution is removed from the sac at each time interval with the help of syringe & it is replaced with fresh buffer solution. The amount of drug that permeates the intestinal mucosa is plotted against time to describe the absorption profile of the drug at any specific pH. 08/10/2010 KLECOP, Nipani

Advantages A number of different solutions may be tested with a single segment of the intestine unlike in the sac technique. Simple & reproducible. It distinguishes between active & passive absorption. It determines the region of the small intestine where absorption is optimal, particularly in the case of active transport. Also used to study the effect of pH, surface active agents, complexation & enzymatic reaction. 08/10/2010 KLECOP, Nipani

Disadvantages The intestinal preparation is removed from the animal as well as from its blood supply. Under these conditions, the permeability characteristics of the membrane are significantly altered. The rate of transport of drug as determined from the everted sac technique, may be slower than in the intact animal. 08/10/2010 KLECOP, Nipani

Circulation technique Small intestine may or may not be everted. In this method either entire small intestine of small lab animal or a segment is isolated. Oxygenated buffer containing the drug is circulated through the lumen. Drug free buffer is also circulated on the serosal side of the intestinal membrane & oxygenated. Absorption rate from the lumen to the outer solution are determined by sampling both the fluid circulating through the lumen. 08/10/2010 KLECOP, Nipani

Advantages This is applicable to kinetic studies of the factors affecting drug absorption. Both surface are oxygenated. Eversion is not necessary. 08/10/2010 KLECOP, Nipani

Everted intestinal ring or slice technique The entire small intestine(everted) is isolated from fasted expt animal Intestine cut wit scalpel or scissors into ring like slices, 0.1-0.5cm length Intestine washed with buffer & dried by blotting with filter paper Dried rings transferred to stoppered flask containing buffer with drug at 37oC Contd… 08/10/2010 KLECOP, Nipani

Contents are continuously agitated & aerated. At selected time intervals, the tissues slices are assayed for drug content 08/10/2010 KLECOP, Nipani

Advantages DISADVANTAGES Simple & reproducible. Kinetic studies can be performed. DISADVANTAGES Process of cutting the intestine into rings may expose highly permeable areas of cut or damage tissue to medium. MAJOR DISADVANTAGE OF IN-VITRO METHODS is that the are based on approximation & oversimplification of the actual in-vivo conditions. 08/10/2010 KLECOP, Nipani

In-situ methods Absorption from small intestine. Perfusion technique. Intestinal loop technique. Absorption from the stomach. 08/10/2010 KLECOP, Nipani

Why in-situ studies. In this method the animals blood supply remains intact & thus the results of rate of absorption determined may be more realistic than those from in-vitro techniques. Alternative means to in-vivo models in evaluating the relative contribution of GI absorption to oral bioavailability. Act as bridge between in-vitro & in-vivo methods. Mimic the in-vivo physiological process with significant reduction in cost & time. 08/10/2010 KLECOP, Nipani

ABSORPTION FROM SMALL INTESTINE PERFUSION TECHNIQUE Adult male rats fasted for about 16-24hrs. Animal anesthetized, a midline abdominal incision is made. isolation & cannulation of Small intestine 08/10/2010 KLECOP, Nipani Contd…

Replacement of intestine. Incision closed & duodenal cannula is attached to an infusion pump Intestine cleared off particulate matter using drug free buffer (1.5ml/30min) Drug buffer solution is perfused (1.5ml/30min) 08/10/2010 KLECOP, Nipani Contd…

Samples assayed for drug content Samples at 10min interval collected from ileal cannula Samples assayed for drug content Relative rate of absorption calculated Relative rate of absorption = difference in the drug concentration entering & leaving the intestine 08/10/2010 KLECOP, Nipani

Figure 08/10/2010 KLECOP, Nipani

Intestinal loop technique Here, single or multiple intestinal loops are used for studying absorption Adult male rat fasted & water with held for 1-2hrs before expt. Under anesthesia an abdominal incision is made & small intestine exposed. Placement of proximal ligature & distal ligature. Introduction of drug solution. 08/10/2010 KLECOP, Nipani Contd..

Replacement of intestinal loop. After a predetermined period of time, animal is sacrificed. Intestinal loop is rapidly excised & homogenized. The amount of drug unabsorbed is determined. 08/10/2010 KLECOP, Nipani

Advantages DISADVANTAGES Simple & reproducible. For preparing multiple loops, the procedure is identical to single loop preparation with a distance of approximately one half inch left between successive loops. Advantages Simple & reproducible. DISADVANTAGES Only 1 sample can be obtained from the experimental animal. 08/10/2010 KLECOP, Nipani

Absorption from the stomach Fasted adult male rats anesthetized, stomach exposed & cardiac end ligated. Introduction of cannula (pylorus). Lumen washed several times with saline & subsequently with 0.1N HCl containing 0.15M NaCl Drug solution of known concentration is introduced into the stomach 08/10/2010 KLECOP, Nipani Contd….

DISADVANTAGE % of drug absorbed in 1hr may be calculated. After 1hr, the drug solution is removed from the gastric pouch & assayed for drug content. % of drug absorbed in 1hr may be calculated. The gastric pouch may also be homogenized & analyzed for drug. DISADVANTAGE In-situ techniques equate absorption with loss of drug from the GI lumen & if a drug is significantly accumulated or metabolized in gut wall, one will get an overestimate of the amount of drug absorbed 08/10/2010 KLECOP, Nipani

In-vivo methods Direct method. Indirect method. 08/10/2010 KLECOP, Nipani

Why in-vivo studies Only method to assess the importance of many factors like- Gastric emptying. Intestinal motility. Effect of drug on GIT. The influence of dosage form variables on drug absorption can also be studied. 08/10/2010 KLECOP, Nipani

Direct method The drug level in blood or urine is determined as a function of time. Absorption studies on experimental animals & clinical trials. Selection of experimental animals- pigs, dogs, rabbits, rat. 08/10/2010 KLECOP, Nipani

Procedure A blank urine or blood sample is taken for the test animal before the experiment. Administration of test dosage form. Blood or urine sampling. Assay for drug content & determination of rate & extent of drug absorption. 08/10/2010 KLECOP, Nipani

Indirect method Adopted when the measurement of drug concentration in blood or urine is difficult or not possible. Pharmacological response is taken as the index of drug absorption. LD 50 appears to be dependent on the rate of absorption of drug & hence on the rate of dissolution. A plot of log dose vs. duration of response time is plotted. 08/10/2010 KLECOP, Nipani

Duration of response time y d Log dose Fka/2.303 x Duration of response time Where, F= bioavailability. Ka= the absorption rate constant. d= threshold dose 08/10/2010 KLECOP, Nipani

REFERENCES Biopharmaceutics & pharmacokinetics by D.M.Brahmankar & Sunil B. Jaiswal. Biopharmaceutics & pharmacokinetics by P.L.Madan. Biopharmaceutics & pharmacokinetics by G.R.Chatwal. Human anatomy & physiology by Tortora. www.google.com. 08/10/2010 KLECOP, Nipani

E-mail: bknanjwade@yahoo.co.in Thank you Cell No: 00919742431000 E-mail: bknanjwade@yahoo.co.in 08/10/2010 KLECOP, Nipani