Dr. Muslim Suardi, MSi., Apt. Faculty of Pharmacy University of Andalas

 “The rate & extent to which the active ingredient or active moiety is absorbed from a drug product & becomes available at the site of action  Usually estimated by its concentration in body fluids, pharmacologic response, clinical response, the rate & extent of excretion

 Concerned with how quickly & how much of a drug appears in the blood after a specific dose is administered  The BA of a drug product often determines the therapeutic efficacy of that product since it affects the onset, intensity & duration of therapeutic response of the drug.

Absolute & Relative BA  Determination of absolute BA of a drug usually involves a comparison of AUC obtained following extravascular & IV administration of the drug  Relative BA is obtained by comparing the AUCs when like or unlike dosage forms of the same drug are administered by same or different routes but not iv.

Absorption  Occurs after its release from the dosage form. Release of drug depends on the physical & chemical properties of the drug, the dosage form (delivery system), the site & route of administration.  The physical & chemical characteristics of a drug as well as its formulation are of prime importance in BA because they can affect not only the absorption characteristics of the drug but also its stability.

 Since a drug must be dissolved to be absorbed, its rate of dissolution from a given product must influence its rate of absorption, the onset, & could affect the pharmacologic activity of a drug.  Factors that affects the dissolution rate of slowly dissolving substances is the surface area of the dissolving solid  After the administration of a drug solution, or following the dissolution of a solid dosage form, drug molecules enter into the systemic circulation by crossing one or more biological membranes.

Absorption  Effects of formulation & processing variables on the dissolution of active ingredients from drug products; an apparently inert ingredient may affect drug absorption.  The nature of the dosage form itself may have an effect on drug absorption characteristics. Fastest availability Slowest availability Solutions Suspensions Capsules Tablets Coated tablets Controlled-release formulations

 BA Factors related to the dosage form Physicochemical properties of the drug Formulation & manufacturing variables Particle size Crystalline structure Degree of hydration of crystal Salt or ester form Amount of disintegrant Amount of lubricant Special coatings Nature of diluent Compression force

Factors influence the BA of a drug  BA Factors Related to the patient Physiologic factorsInteractions with other substances Variations in absorption power along GI tract Variations in pH of GI fluids Gastric emptying rate Intestinal motility Perfusion of GIT Presystemic & first-pass metabolism Age, sex, weight Disease states Food Fluid volume Other drugs

Sequence of events after administration of a drug product Method of evaluationExample Dissolution at administration or absorption site Dissolution rateIn vitro: water, buffer, artificial gastric fluid, artificial intestinal fluid, artificial saliva, artificial rectal fluid Free drug in systemic circulation Blood level time profile, Peak blood level, Time to reach peak, Area under blood level time curve In vivo: whole blood, plasma, serum Pharmacologic effectOnset of effect, Duration of effect, Intensity of effect In vivo: discriminate measurement of pharmacologic effect (blood pressure, blood sugar, blood coagulation time) Clinical responseControlled clinical blind or double- blind, Observed clinical success or failure In vivo: evaluation of clinical responses EliminationCumulative amount of drug excreted, Maximum excretion rate, Peak time of excretion In vivo: urine