Math equation stuff for pharm Flashcards
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
bioavailability
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
clearance
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.
