Bioavailability:

It is the rate and amount of drug that is absorbed from a given dosage form and reaches the
systemic circulation following non-vascular administration. When the drug is given IV, the
bioavailability is 100%. It is important to know the manner in which a drug is absorbed. The
route of administration largely determines the latent period between administration and onset of
action. Drugs given by mouth may be inactive for the following reasons:
a) Enzymatic degradation of polypeptides within the lumen of the gastrointestinal tract e.g.
insulin, ACTH.
b) Poor absorption through gastrointestinal tract e.g. aminoglycoside antibiotic.
c) Inactivation by liver e.g. testosterone during first passage through the liver before it reaches
systemic circulation.

3. Factors affecting drug absorption and bioavailability:
   a) Physico-chemical properties of drug
   b) Nature of the dosage form
   c) Physiological factors
   d) Pharmacogenetic factors
4. e) Disease states.