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Pharmacokinetics Dr. Muslim Suardi, MSi., Apt. School of Pharmacy, Faculty of Science University of Andalas Pharmacokinetic ABSORPTION DISTRIBUTION METABOLISM EXCRETION Pharmacokinetic Models • Oversimplified but useful mathematical models for describing the pharmacokinetic behavior of a drug in the body. • Depict the body as a single compartment or a series of compartments. • These compartments do not necessarily have any anatomical or physiological reality. Single Compartment Model Can be most readily applied to drugs that rapidly distribute between blood and tissue after absorption ABSORPTION “Transfer of drug from the administration site to the systematic circulation” a. Barriers of Absorption b. Mechanisms of Absorption Mechanisms of Absorption 1. Passive Diffusion: Most of drugs. 2. Active Transport: Eg. Levodopa. 3. Facilitated Diffusion 4. Pores 5. Pinocytosis 6. Electrochemical diffusion Bioavailability “A measure relative to some standard of the rate & amount of drug which reaches the systemic circulation unchanged following the administration of a suitable dosage form” (BA) Rate of Absorption “Important for rapid onset of effect” Methods for Estimating Rate of Absorption: - Time of peak plasma level - Determine ka - Method of residuals - Percent of unabsorbed - For plots (Large ka - rapid absorption). Extent of Absorption • Absolute Vs Relative BA • Methods for Estimating Extent of Absorption • Plasma levels • Eg. Trapeziodal role • Urinary recovery (if largely excreted unchanged) • (Xu = total amount of unchanged drug excreted in urine) Examples Drug F (oral) % • Ampicillin 50 • Digoxin 50-90 • Warfarin 100 • Penicillin G <30 • Doxycycline 100 Factors Influencing Bioavailability