Issar- Pharmacokinetics 1 and 2

Question 1

what reaction proceeds at a constant rate and is independent of concentration of drug A present in the body?

Answer 1

zero order rate (ex. alcohol)

Question 2

describe first order rate constant.

Answer 2

describes a proportional rate of change of drug A with time (linear)

Question 3

what makes up the characteristics of a compartment?

Answer 3

not real anatomic region, uniform distribution within each, open system, well-stirred, rates constants represent drug entry or exit

Question 4

what type of drugs show/demonstrate nonlinear pharmacokinetics or zero-order reactions?

Answer 4

drugs with accumulation in the plasma levels

Question 5

what do most processes of ADME follow?

Answer 5

first-order reactions

Question 6

what happens to first-order drugs if you increase the amount of drugs until system is saturated (ex. overdose)?

Answer 6

drug will change from first-order to zero-order (mixed-order kinetics) - phenytoin and salicylic acid

Question 7

what happens to a drug in a one-compartment model?

Answer 7

achieves instantaneous distribution throughout body and between tissues and follows first order kinetics

Question 8

what happens to a drug in a two-compartment model?

Answer 8

drug distributes between central and peripheral compartment - but not instantaneous distribution (biphasic response)

Question 9

what is the equation for Vd? and what is it used for clinically?

Answer 9

Vd = amount of drug in body/concentration in plasma; calculate appropriate blood concentration of drug in patient

Question 10

what is the equation to calculate an appropriate dose of a drug?

Answer 10

Dose = Cp x Vd

Question 11

what is drug clearance?

Answer 11

the volume of plasma fluid that is cleared of drug per unit of time (not how much drug is being removed)

Question 12

what is the equation for body Cl?

Answer 12

Cl body = elimination rate/plasma concentration

(dDb/dt)/Cp or -kelim x Vd

Question 13

what is half-life?

Answer 13

time it takes for plasma concentration of drug to fall by 50% regardless of initial value - meaningful if drug follows first-order kinetics

Question 14

How do you calculate half-life?

Answer 14

half-life = 0.693/Kelim
T 1/2 = (0.639 x Vd)/Cl
Kelim = Cl/Vd

Question 15

what happens to half-life if there is a decrease in Vd and an increase in clearance?

Answer 15

half-life will be shortened

Question 16

What is it called when the infusion rate matches the elimination rate for a drug?

Answer 16

steady state (Css = rate of infusion/clearance)

Question 17

why would you use a loading dose?

Answer 17

to achieve steady state faster with an infusion (loading dose = target concentration x Vd) - drugs with long half lives

Question 18

what is the relationship between accumulation period and half life?

Answer 18

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)

Question 19

what is pharmacokinetic accumulation?

Answer 19

occurs when a dose is given while there is a large residue still present in the body (drug has slower elimination rate)

Question 20

why does pharmacokinetic accumulation not happen indefinitely?

Answer 20

dosing intervals - the drug has reached Css and elimination = incoming dose

Question 21

What is the equation for Css Average?

Answer 21

Css,Avg = (F x D)/ Cl x tau

Question 22

what are the 3 factors that influence extent of fluctuation?

Answer 22

half-life, dose division, and dosage form (Half-life is the most influential)

Question 23

why are short half-life drugs problematic? and what are 2 ways to moderate it?

Answer 23

produce more fluctuations and brings risk of complications - dose division and slow release formulas

Question 24

why does dose division reduce drug fluctuations?

Answer 24

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)

Question 25

how do slow release formulas help decrease drug fluctuations?

Answer 25

slow release gives a shorter period of decline and the low troughs are eliminated