Pharmacokinetics - Chapter 4 PDF

**[Chapter 4]** **[Pharmacokinetics]** **[1-Absorbtion:]** The movement of drug from site of administration into blood done by passive diffusion. Influencing factors: concentration gradient, drug size and lipid solubility. **[Membrane permeability:]** - Uncharged hydrophobic drugs can diffuse...

**[Chapter 4]** **[Pharmacokinetics]** **[1-Absorbtion:]** The movement of drug from site of administration into blood done by passive diffusion. Influencing factors: concentration gradient, drug size and lipid solubility. **[Membrane permeability:]** - Uncharged hydrophobic drugs can diffuse across lipid bilayer - Drugs are weak acids HA^-^-\>H^+^ + A^-^ - PH and pKa dictates which form the drug takes - Only uncharged species enter the membrane - PH= pka + log (unprotonated form/protonated form) Ex: if we take tums while taking pain relief drug the pain won't go away because the drug doesn't do it's effect seeing as tums raise pH by 2 units making it less acid. **[Bioavailibility:]** It is the ammount of drug reaching systemic circulation unchanged F= amount of drug in syst cyrc/amount of drug taken IV is F=1 100% Bioavailibility Oral drug can never have F=1 because GI tract absorbs, metabolizes or degrades the drug and liver metabolizes it also **[2-Distribution:]** It is the process in which the drug moves between body compartments to it's site of action through the bloodstream (reversibly) Influencing factors: Conc gradient, drug size, lipid solubility Drug arrives to tissues through perfusion: first to brain, heart, liver and kidneys then to skeletal muscles and skin and finaly to adipose tissue. Effect of protein binding: Drugs reversibly bind plasma proteins, proteins are large sequester drug in blood that makes drug inactive and makes concentration of free drug decrease Volume of distribution is a proportionality constant that indicates the extent of drug distribution but not the location. Vd\>42L good distribution to tissues but if V=\