Biopharmaceutics & Pharmacokinetics

Biopharmaceutics & Pharmacokinetics

SALMAN BIN ABDUL AZIZ UNIVERSITY COLLEGE OF PHARMACY PHARMACEUTICS- IV (PHT 414 ) Gastrointestinal absorption (Membrane physiology, biological consideration) Dr. Mohammad Khalid Anwer 02/22/2020 LEC2 1 Absorption Absorption: it is defined as the process of movement of unchanged drug from the site of administration to systemic circulation . Mechanisms by which drugs may cross membranes:

Passive diffusion Facilitated diffusion Osmosis Active transport Passive diffusion MUCH more common than any of the others. 02/22/2020 LEC1 2 02/22/2020 LEC2 3

Requirements for passive diffusion Water solubility Lipid solubility * Almost all drugs are sufficiently water soluble to undergo passive diffusion, but some do lack the necessary lipid solubility. * In practice, passive diffusion depends mainly on lipid solubility. 02/22/2020 LEC2 4 Membranes and Absorption Lipid Bilayer Hydrophilic Hydrophilic Heads Heads

Small, uncharged H2O, urea, CO2, O2, N2 Large, uncharged Glucose Sucrose Small charged ions 02/22/2020 H+, Na+, K+, Ca2+, Cl-, HCO3- LEC2

Hydrophobi Hydrophobi ccTails Tails Swoosh! DENIED! DENIED! 5 Acidic drugs are best absorbed from acidic environments Basic Basic drugs drugs are are best best absorbed absorbed from from

basic basic environments environments 02/22/2020 LEC2 6 So... To Toabsorption absorptionof ofan anacidic acidicdrug drug acidify acidifythe theenvironment environment To

Toabsorption absorptionof ofan anacidic acidicdrug drug alkalanize alkalanizethe theenvironment... environment... 02/22/2020 LEC2 7 Factors Affecting Liberation/Absorption Patient Formulation factors factors Absorbing

Tablet disintegration surface Blood Inert ingredient flow / solvent effects Environmental Solubility pH Disease Drug pHstates Interactions Concentration with food, other drugs 02/22/2020 LEC2 8

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