PCL201H1 Lecture Notes - Lecture 9: Body Composition, Lipophilicity, Extracellular Fluid
14 Sep 2016
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Following administration and absorption, the drug distributes from the systemic circulation to intracellular and interstitial fluid. Distribution depends on: physiochemical properties of the drug, plasma protein and tissue binding, blood flow and capillary permeability, patient-related factors. Tbw varies with: body composition (obese vs. lean, age (children vs. elderly, gender. Small molecules (e. g. ethanol) with no protein binding or tissue accumulation equilibrate with tbw. Drugs must permeate cell membranes to reach the icf (to act on intracellular targets) Drugs distribute through the ecf faster than permeating membranes (to act on surface receptors) Plasma: liquid portion of the blood: serum is plasma without clotting factors, drug concentration often measured in plasma or serum dependent on hematocrit. Drugs (especially acidic ones) may reversibly bind to proteins like 1-glycoprotein and albumin cannot permeate barriers and remain in the blood. Drugs that localize are unequally distributed and remain longer in the body: define the term volume of distribution (vd)
