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pharmacokinetics vs. pharmacodynamics

kinetics: effects of the body on the drug: absorption, distribution, metabolism, excretion (ADME)
dynamics: effects of the drug on the body: receptor binding, drug efficacy, potency, toxicity



the fraction of the administered drug that reaches the systemic circulation unchanged. usually 100% for an IV drug and less than 100% for an oral drug d/t incomplete absorption and first-pass metabolism


volume of distribution; effects of liver/kidney disease on Vd

Vd = amt of drug in the body/plasma drug concentration. measures distribution to other compartments. liver and kidney disease may incr. the Vd the Vd because of decr. protein binding


low Vd: compartment, drug types

low Vd means most of the drug is in the blood. usually seen in drugs that are larged, charged, or protein-bound


medium Vd: compartment, drug types

drug in the ECF. seen with small hydrophilic molecules


high Vd: compartment, drug types

compartment: all tissues, incl. fat
seen in small lipophilic molecs, esp. if bound to tissue protein


half life: equation.

half life = (0.7 X Vd)/clearance


How many half lives to reach steady state?

4-5 half lives; 3.3 to reach 90% of steady state



CL = rate of elim of a drug/ plasma drug conc = Vd X Ke (elimination constant) = (.7 X Vd)/half life
in words, this is the vol. of plasma cleared of drug per unit time. may be impaired with defects in cardiac, hepatic, or renal function


loading dose

(Cp X Vd)/F. Cp is the target plasma concentration at steady state. F = bioavailibility.


maintenance dose

(Cp X clearance X dosage interval if not continuous)/ bioavailability


effect of renal and liver disease on maintenance dose and loading dose

typically maintenance dose is decr. but loading dose is not changed.