Q. DEFINE BIOAVAILABIITY AND FACTORS AFFECTING IN THE DRUG ABSOPTION .
Bioavailability - The rate and extent of absorption of drug from dosage form reaches to systemic circulation.
OR
Amount of percentage of drug that is absorbed from administered dosage form and reaches to systemic circulation after non vascular administration.
Factors affecting drug absorption -
- Particle size of drug - The rate of of absorption is inversely proportional to size of particle. Smaller the particle size the absorption rate will maximum.
- Physical state of drug - Crystalline drug shows minimum absorption than the amorphous drug. Lipids are better absorbed than solids.
- Absorbing surface - Drug absorption is directly proportional to surface area. Due to large surface area of intestine there will be more absorption than stomach.
- Functional integrity of GIT - Absorption of drug from GI tract may be effectively decrease by increase in peristaltic activity. Increase in peristalsis reduces contact time of drug in GIT.
- PH of drug -
- acidic drugs are rapidly absorbed from stomach. e.g. salicylate barbiturate
- Basic drugs are absorbed in small intestine. e.g. ephedrine
- Ionization factor - Unionized drug shows greater absorption tha ionized drug due to formation of ion.
- Solubility - The rate of absorption is maximum of lipid soluble drug. Water soluble drug is poorly absorbed.
- Presence of food - The content of food affects absorption of drug.
- Disease condition - The absorption rate is depending upon various physical condition of human being. Healthy person shows better absorption rate.
- Route of administration - Sublingual route and topical route shows better absorption than oral route.
- Formulation - Liquid dosage form shows better absorption than solid dosage form.
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