Question

1.Many factors affect drug absorption. Select five (5) of these factors and provide a rationale or mechanism(s) for each one’s effects on drug absorption. Use examples to clarify your answer.

Answer 1

1.Many factors affect drug absorption. Select five (5) of these factors and provide a rationale or mechanism(s) for each one’s effects on drug absorption. Use examples to clarify your answer.

Factors affecting drug absorption are:

1. Route of administration

Drugs are administered according to the preparation form and the efffect is desired.Parentral administration is generally rapid.Drugs administered by intravenous or intra-arterial route have rapid absorption than intramuscular or subcutaneous.Speed absorption depends on blood circulation. Absorption is slow and confined to area if drugs given intradermally.

eg. Injection insulin administered via intravenous route directly enter into blood stream . if insulin administering subcutaneously, it takes around 15-30 mts to begin therapeutic action.

2. solubility of drugs

Aqueous form of drugs dissolves in water, hence absorption takes place rapidly from the intestine.But lipid soluble drugs affect absorption as it passes through gastrointestinal tract. In contrast lipophilic drugs easily cross cell membrane by active transport mechanism.

eg. glucose, vitamin B12 absorbed from intestine through simple diffusion

3.Form of drug: Syrup, suspension, are absorbed rapidly than tablet or capsules.Because tablets dissolves first into ganules then into small molecules.Intavenous solutions directly administered into blood stream and provide therapeutic action immediately.

4. Time of administration :

In the administration of oral drugs, the time of administration is highly important. When the stomach is empty of foods, the drugs are absorbed rapidly into the circulation. In contrast , diarrhoea can cause drugs not to be absorbed.Constipation may delay the absorption, leads to toxicity.

eg. Levothyroxin - administered in early morning to enhance absorption.

Pantoprazole- administered 30mts before meal.

5. pH of the drugs

Acidic drugs absorbed well in acid medium and base form of drugs absorbed well in alkaline medium.

eg. drug such as Aspirin absorbed from stomach. ( acidic drug)

drug such as Diazepam absorbed from intestine ( basic drug)