These factors are important for: attaining desired drug conc. in the body + sustaining concentrations for desired length of time + drug removal after desired effect is attained.
Biopharmaceutics affords a basic understanding of the processes of drug absorption, distribution and elimination + potential effects of dosage form on these processes that can be applied to optimize therapeutic outcome of a patient.
Dosage form of a drug exerts its major influence on the absorption process
Schematic illustration of the steps involved in the appearance of intact drug in systemic circulation following oral administration of a tablet STOMACH (Gastric content. pH 1-3) SMALL INTESTINE (Intestinal cont. pH 5-7) Tablet Granules Fine particles Dissolution Drug in solution Tablet Granules Fine particles Dissolution Drug in solution Absorption Intact drug Liver Intact Drug in systemic Circulation Pharmacologic effect Intestinal metabolism Metabolites Urine Hepatic Metabolism (1 st Pass Effect) Disintegration Deaggregation
Rate Limiting Steps of Absorption Rate of metabolism of drug during its initial passage through the liver (i.e. First-pass effect). Rate at which drug is metabolized by the enzymes in the intestinal mucosal cells en route into mesenteric blood vessels Rate of gastric emptying into small intestine Other factors Rate of release from the dosage form Dosage Design Rate at which drug crosses membrane of the GIT High aqueous solubility Rate of dissolution in gastrointestinal fluid Poor aqueous solubility Rate Limiting Step Nature of Drug