1. ROUTES OF ADMINISTRATION
LECTURE 2
PHARMACOLOGY
ROUTES OF ADMINISTRATION

2. Drug Absorption
Absorption is the process by which a drug enters the bloodstream without being chemically altered or
The movement of a drug from its site of application into the blood or lymphatic system

3. Drug Absorption Factors which influence the rate of absorption
types of transport
the physicochemical properties of the drug
protein binding
routes of administration
dosage forms
circulation at the site of absorption
concentration of the drug

4. Drug Absorption
The rate at which a drug reaches it site of action depends on:
Absorption - involves the passage of the drug from its site of administration into the blood
Distribution - involves the delivery of the drug to the tissues

5. Drug Absorption Mechanisms of solute transport across membranes
passive diffusion
filtration and bulk flow
endocytosis
ion-pairing
active transport
Drug Absorption animation

7. Ion Trapping cont:
Body fluids where a pH difference from blood pH will favor trapping or reabsorption: stomach contents
small intestine
breast milk
aqueous humor (eye)
vaginal secretions
prostatic secretions

8. Ion Trapping:
Kidney:
Nearly all drugs filtered at the glomerulus:
Most drugs in a lipid-soluble form will be absorbed by passive diffusion.
To increase excretion: change the urinary pH to favor the charged form of the drug:
Weak acids: excreted faster in alkaline pH (anion form favored)
Weak bases: excreted faster in acidic pH (cation form favored)

9. Lipid-Water Partition Coefficient
The ratio of the concentration of the drug in two immiscible phases: a nonpolar liquid or organic solvent (representing the membrane); and an aqueous buffer, pH 7.4 (representing the plasma)

10. Lipid-Water Partition Coefficient
The higher the lipid/water p.c. the greater the rate of transfer across the membrane
INCREASING the polarity of a drug, by increasing ionization will increase the lipid/ water p.c.
DECREASING polarity of a drug, suppression of ionization will decrease the lipid/ water p.c.

11. Routes of Drug Administration
The route of administration (ROA) that is chosen may have a profound effect upon the speed and efficiency with which the drug acts

13. The possible routes of drug entry into the body may be divided into two classes:
Enteral
Parenteral

14. Enteral Routes sublingual - placed under the tongue
Enteral - drug placed directly in the GI tract:
sublingual - placed under the tongue
oral - swallowing (p.o., per os)
rectum - Absorption through the rectum

15. Sublingual/Buccal Advantages
Some drugs are taken as smaller tablets which are held in the mouth or under the tongue.
Advantages
rapid absorption
drug stability
avoid first-pass effect

16. Sublingual/Buccal Disadvantages inconvenient small doses
unpleasant taste of some drugs

17. Oral
Advantages
Convenient - can be self- administered, pain free, easy to take
Absorption - takes place along the whole length of the GI tract
Cheap - compared to most other parenteral routes

18. Oral
Disadvantages
Sometimes inefficient - only part of the drug may be absorbed
First-pass effect - drugs absorbed orally are initially transported to the liver via the portal vein
irritation to gastric mucosa - nausea and vomiting

19. Oral Disadvantages cont.
destruction of drugs by gastric acid and digestive juices
effect too slow for emergencies
unpleasant taste of some drugs
unable to use in unconscious patient

20. First-pass Effect
The first-pass effect is the term used for the hepatic metabolism of a pharmacological agent when it is absorbed from the gut and delivered to the liver via the portal circulation. The greater the first-pass effect, the less the agent will reach the systemic circulation when the agent is administered orally

21. First-pass Effect cont.
Magnitude of first pass hepatic effect: Extraction ratio (ER)
ER = CL liver / Q ; where Q is hepatic blood flow (usually about 90 L per hour.
Systemic drug bioavailability (F) may be determined from the extent of absorption (f) and the extraction ratio (ER):
F = f x (1 -ER)

22. First-pass Effect

23. Rectal 1. unconscious patients and children
2. if patient is nauseous or vomiting
3. easy to terminate exposure
4. absorption may be variable
5. good for drugs affecting the bowel such as laxatives
6. irritating drugs contraindicated

24. Parenteral Routes
Intravascular (IV, IA)- placing a drug directly into the blood stream
Intramuscular (IM) - drug injected into skeletal muscle
Subcutaneous - Absorption of drugs from the subcutaneous tissues
Inhalation - Absorption through the lungs

27. Intravascular 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
c. OOPS factor or

28. Intramuscular 1. very rapid absorption of drugs in aqueous solution
2.repository and slow release preparations
3.pain at injection sites for certain drugs

29. Subcutaneous 1. slow and constant absorption
2. absorption is limited by blood flow, affected if circulatory problems exist
3. concurrent administration of vasoconstrictor will slow absorption

30. Inhalation 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.

31. Inhalation cont. Respiratory system. Except for IN, risk hypoxia.
Intranasal (snorting) Snuff, cocaine may be partly oral via post-nasal dripping. Fairly fast to brain, local damage to septum. Some of the volatile gases also appear to cross nasal membranes.
Smoke (Solids in air suspension, vapors) absorbed across lung alveoli: Nicotine, opium, THC, freebase and crack cocaine, crystal meth.Particles or vapors dissolve in lung fluids, then diffuse. Longer action than volatile gases. Tissue damage from particles, tars, CO.
Volatile gases: Some anaesthetics (nitrous oxide, ether) [precise control], petroleum distillates. Diffusion and exhalation (alcohol).
Lung-based transfer may get drug to brain in as little as five seconds.

32. Topical
Mucosal membranes (eye drops, antiseptic, sunscreen, callous removal, 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 or patch becomes to large

33. Route for administration
-Time until effect-
intravenous seconds
intraosseous seconds
endotracheal 2-3 minutes
inhalation 2-3 minutes
sublingual 3-5 minutes
intramuscular minutes
subcutaneous minutes
rectal 5-30 minutes
ingestion minutes
transdermal (topical) variable (minutes to hours)

34. Time-release preparations
Oral - controlled-release, timed-release, sustained-release
designed to produce slow,uniform absorption for 8 hours or longer
better compliance, maintain effect over night, eliminate extreme peaks and troughs

35. Time-release preparations
Depot or reservoir preparations - parental administration (except IV), may be prolonged by using insoluble salts or suspensions in non-aqueous vehicles.

36. The ROA is determined by the physical characteristics of the drug, the speed which the drug is absorbed and/ or released, as well as the need to bypass hepatic metabolism and achieve high conc. at particular sites

37. No single method of drug administration is ideal for all drugs in all circumstances

38. Thank you