Absorption of drug (A):

• The process by which the drug enter into systemic circulation is called absorption of drug. All routes of drugs have to enter systemic circulation to exert their pharmacological effects. For this, drug have to cross the biological membranes.
• Both the rate and extent of drug absorption are important because they determine the duration and intensity of drug action. Drug that is completely but slowly absorbed fails to show therapeutic response as minimum effective concentration is never reached.
• Rapidly and completely absorbed drug attains the therapeutic level easily to elicit its pharmacological effect.
• Drug must be in solution form to be absorbed. Solid forms must be able to disintegrate and dissolve body fluids.