ROUTES OF DRUG ADMINISTRATION

Definition: A route of administration is the path by which a drug, fluid, poison or other substance is brought into contact with the body.

FACTORS GOVERNING CHOICE OF ROUTE Physical and chemical properties of drug(water or lipid solubility , ionization ) Site of desired action Rate & extent of absorption from various routes Effect of digestive juices & first pass effect Rapidity of the desired response Condition of the patient

Classification A- Enteral B-Parenteral & other routes One method of classifying The possible routes of drug entry into the body may be divided into two classes: A- Enteral B-Parenteral & other routes

Routes of administration

For a drug to be able to produce its intended clinical effects, -It must first be able to reach its target site of action in the body at an effective concentration. If the drug is to act on some external surfaces, e.g., skin, ears or eyes, it may be applied directly on the affected surface. If the drug is meant to produce an effect inside the body, whether it be widespread (e.g., systemic antibiotics) or on some specific tissues (e.g., anti-thyroid agents), then the drug must be administered in such a way that it is able to get into the systemic circulation and be transported to the site (s).

A- Enteral - drug placed directly in the GI tract: 1- Oral route:- By swallowing. - It is intended for systemic effects resulting from drug absorption through the various epithelia and mucosa of the gastrointestinal tract. ex aspirin, paracetamol

Advantages: 1- Convenient - portable, no pain, easy to take and economical 2- Cheap - no need to sterilize, compact, multi-dose bottles, 3- Variety - tablets, capsules, suspensions, mixtures . 4- Usually good absorption 5- Danger of acute drug reaction is minimal

DISADVANTAGES Can not used in unconcious patients Some drugs destroyed and first –pass effect . Food and G-I motility can affect drug absorption. Often It recommended taking it on an empty stomach. Absorption is slower with food(milk and milk products) for tetracyclines and penicillins, etc.

First pass effect: Drugs absorbed orally are transported to the general circulation via the liver. Thus drugs which are extensively metabolized will be metabolized in the liver during absorption

Sometimes may have adverse reactions – e. g Sometimes may have adverse reactions – e.g. Antibiotics may kill normal gut flora and allow overgrowth of fungal varieties. Thus, antifungal agent may be included with an antibiotic. Not suitable for unconscious patient - Patient must be able to swallow solid dosage forms. Liquids may be given by tube.

2- Buccal/Sublingual route: Some drugs are taken as smaller tablets which are held in the mouth (buccal tablet) or under the tongue (sublingual tablet). Buccal tablets are often harder tablets [4 hour disintegration time], designed to dissolve slowly. E.X: Nitroglycerin, as a softer sublingual tablet [2 min disintegration time], may be used for the rapid relief of angina.

Advantages 1- Avoid hepatic first pass - The liver is by-passed thus there is no loss of drug by first pass effect for buccal administration. Bioavailability is higher. 2- Rapid absorption - Because of the good blood supply to the area, absorption is usually quite rapid. 3- Drug stability - pH in mouth relatively neutral (gf. stomach - acidic). Thus a drug may be more stable.

Disadvantages 1- Holding the dose in the mouth is inconvenient. 2- Drug taste may need to be masked 3- Small doses only can be accommodated easily.

3-Rectal route: Advantages Most commonly by suppository or enema. Advantages 1- By-pass liver - Some of the veins draining the rectum lead directly to the general circulation, thus by-passing the liver. Reduced first-pass effect. 2- Useful - This route may be most useful for patients unable to take drugs orally (unconscious patients) or with younger children. or vomiting

Disadvantages 1- Erratic absorption - Absorption is often incomplete and erratic. 2- Not well accepted. AND Irritation or inflammation of rectal mucosa can occur

B-parenteral route Administration by the parenteral route can involve all routes other properties includes 1- provide a rapid onset of action (100% bioavailability) 2- to ensure high blood levels of the drug. 3- The parenteral route also is used when the GI route would inactivate the drug, 4- in unconscious patients, and in unstable or seriously ill patients who require precise administration and monitoring. 5- In acute care medicine, administration is almost always parenteral because the onset of action

1-intravascular route (intravenous and intra arterial route) .( I.V.). placing a drug directly into blood stream. May be - Intravenous (into a vein) or intraarterial (into an artery).

Intravenous (I.V)

Advantages Precise, accurate and almost immediate onset of action Total dose - The whole dose is delivered to the blood stream. Large doses can be given by extending the time of infusion. Veins relatively insensitive to irritation by irritant drugs. Not occur vomiting &diarrhea Given in Emergency situations. Larger doses may be given by IV infusion over an extended time.

Disadvantages Vein may be difficult to locate. May be toxic - Because of the rapid response, toxicity can be a problem with rapid drug administrations Pain at the site of injection Greater risk of adverse effects and risk of embolism I/v injection requires technical skill to minimize the risk of leakage of irritant solution into the surrounding tissues. Expensive - Sterility, pyrogen testing and larger volume of solvent means greater cost for preparation, transport and storage.

Intramuscular injection(I.M) Injection is made deep into the muscle tissue. In humans, the best site is deltoid muscle in the shoulder or the gluteus muscle in femeral and , triceps The speed of absorption from site of injection is dependent on the vehicle used, absorption is quick from aqueous solutions and slow from oily preparations. Absorption is complete, predictable and faster than subcutaneous route.

Parenteral route:

Advantages Larger volume, than sc, can be given by IM Very rapid absorption of drugs in aqueous solution A depot or sustained release effect is possible with IM injections, e.g. procaine penicillin First pass and gastric factors can be avoided.

Disadvantages 1.pain at injection sites for certain drugs. 2- The solvent maybe absorbed faster than the drug causing precipitation of the drug at the site of injection 3- Local irritation at site of administration.

A diabetic patient making subcutaneous injection Subcutaneos(S.C) In this route of administration the drug(small volume) is given into the a needle is inserted into fatty tissue just beneath the skin. with the help of injection. such as heparin and insulin A diabetic patient making subcutaneous injection

Subcutaneous Injection

Advantages It is a good route of administration especially in skin infections. 2-It is relatively safer than I.M. and I.V. 3-Absorption is slower thus, it is a good route of a prolonged effect is to be achieved Absorption can be fast from aqueous solution but slower with depot formulations. Improved by massage or heat e.g. Another form of the depot preparation is subcutaneous implant

Disadvantages If the drug is irritating it might cause the sloughing off of the skin epithelial tissue. 2- Can be painful. Finding suitable sites for repeat injection can be a problem. Maximum of 2 ml injection thus often small doses limit use.

Other methods include 1-Inhalation: May be used for a local effect, e.g. bronchodilators. Can be used for systemic effect, e.g. general anesthesia. Rapid absorption by-passing the liver. Administration involves inhaling of a drug in gas or liquid form; drug is absorbed through alveoli of the lungs . Medications can be administered directly into the respiratory tree in cases of respiratory distress Advantages A- Large surface area B- thin membranes separate alveoli from circulation C- high blood flow As result of that a rapid onset of action due to rapid access to circulation.

Metered dose inhaler

2-Intranasal : This route involves administration of drugs directly in to the nose . Agents include nasal decongestants such as the anti inflammatory corticosteroid ,desmopressin is administered intranasally in treatment of diabetes insipidus.

3-Topical: drugs can be placed on the skin, where they are slowly absorbed into the capillary network underneath the skin. rate of onset varies, but the duration of action is prolonged. applied directly on the mucous membranes of the eye, ear, nose, or mouth effect usually local, not systemic, e.g. Bacitracin antibiotic ointment ,nasal decongestant, eye drops.

transdermal Drugs can be injected into the dermal layer of the skin. The amount of medication that can be given via this route is limited, and systemic absorption (into the bloodstream) is very slow. Generally, this route is reserved for diagnostic skin tests, such as allergy testing. Used for slow continuous administration for long duration Usually no first pass effect and Drug can be removed if required. E.X: Patches attached to skin

Intrathecal (intraventricular) This is a route of administration of drug in which the effects of the drug is desired in the C.N.S. The blood brain barrier and the blood cerebrospinal fluid barrier often slow the entrance of drug into the C. N. S. The drug will be accessible to the meningitis. The injection made in the lumbar area . Local anesthetics are sometimes administered intrathecally to produce region or spinal anesthesia.

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