Issar- Pharmacokinetics 1 and 2 Flashcards
what reaction proceeds at a constant rate and is independent of concentration of drug A present in the body?
zero order rate (ex. alcohol)
describe first order rate constant.
describes a proportional rate of change of drug A with time (linear)
what makes up the characteristics of a compartment?
not real anatomic region, uniform distribution within each, open system, well-stirred, rates constants represent drug entry or exit
what type of drugs show/demonstrate nonlinear pharmacokinetics or zero-order reactions?
drugs with accumulation in the plasma levels
what do most processes of ADME follow?
first-order reactions
what happens to first-order drugs if you increase the amount of drugs until system is saturated (ex. overdose)?
drug will change from first-order to zero-order (mixed-order kinetics) - phenytoin and salicylic acid
what happens to a drug in a one-compartment model?
achieves instantaneous distribution throughout body and between tissues and follows first order kinetics
what happens to a drug in a two-compartment model?
drug distributes between central and peripheral compartment - but not instantaneous distribution (biphasic response)
what is the equation for Vd? and what is it used for clinically?
Vd = amount of drug in body/concentration in plasma; calculate appropriate blood concentration of drug in patient
what is the equation to calculate an appropriate dose of a drug?
Dose = Cp x Vd
what is drug clearance?
the volume of plasma fluid that is cleared of drug per unit of time (not how much drug is being removed)
what is the equation for body Cl?
Cl body = elimination rate/plasma concentration
(dDb/dt)/Cp or -kelim x Vd
what is half-life?
time it takes for plasma concentration of drug to fall by 50% regardless of initial value - meaningful if drug follows first-order kinetics
How do you calculate half-life?
half-life = 0.693/Kelim
T 1/2 = (0.639 x Vd)/Cl
Kelim = Cl/Vd
what happens to half-life if there is a decrease in Vd and an increase in clearance?
half-life will be shortened
What is it called when the infusion rate matches the elimination rate for a drug?
steady state (Css = rate of infusion/clearance)
why would you use a loading dose?
to achieve steady state faster with an infusion (loading dose = target concentration x Vd) - drugs with long half lives
what is the relationship between accumulation period and half life?
after the time for the first half life has occurred to drug will be at half the projected Css (Css takes about 3-4 half lives)
what is pharmacokinetic accumulation?
occurs when a dose is given while there is a large residue still present in the body (drug has slower elimination rate)
why does pharmacokinetic accumulation not happen indefinitely?
dosing intervals - the drug has reached Css and elimination = incoming dose
What is the equation for Css Average?
Css,Avg = (F x D)/ Cl x tau
what are the 3 factors that influence extent of fluctuation?
half-life, dose division, and dosage form (Half-life is the most influential)
why are short half-life drugs problematic? and what are 2 ways to moderate it?
produce more fluctuations and brings risk of complications - dose division and slow release formulas
why does dose division reduce drug fluctuations?
giving the dose at more frequent intervals and smaller doses keeps concentration in desirable range instead of oscillating between toxic and effective (be careful with non-compliance)
how do slow release formulas help decrease drug fluctuations?
slow release gives a shorter period of decline and the low troughs are eliminated
