Pharmacokinetics

Question 1

First order kinetics

Answer 1

Rate of abs or elimination is directly proportional to concentration
t1/2=.693/k

k and t1/2 DO NOT change with increased dosage

But, bc concentration declines, rate decreases as well

Question 2

Zero order kinetics

Answer 2

rate is independent of dose
occurs in situations where the mechanism of elimination is saturated (i.e. enzyme), therefore elimination occurs at a constant rate
Examples: ETOH, ASA at high doses

Question 3

Mass-law kinetics

Answer 3

a mixed order system
at low doses= first order kinetics
high doses=saturation of enzymes= zero-order

Question 4

Volume of distribution

Answer 4

apparent volume of fluid in which drug is distributed
=loading dose/plasma concentration

Increased Vd= slower rate of elimination (drug is more spread out)

Vd>41 could indicated that much of the drug is sequestered in fat

Question 5

total body clearance

Answer 5

volume of fluid from which drug is totally removed per unit time
describes efficiency of elimination pathways (metabolism and excretion)

Cl= Vd x Ke

Question 6

peak concentration

Answer 6

proportional to dose (double dose = double peak)

Question 7

duration of concentration in a single dose

Answer 7

only increases as function of half-life

duration increases by a single half-life as dose is doubled

Question 8

Plateau Principle

Answer 8

Input= Constant rate (zero order)- i.e. give multiple doses
Output= exponential (first order)
Rate to plateau determined by Ke
Plateau reached by 5 elimination half-times

concentration at plateau is doubled when dose is doubled (still takes 5 half-times to get there)

Question 9

bioavailability

Answer 9

(f)= fraction of the dose that is absorbed and reaches systemic circulation (i.e. w/o being destroyed in gut or liver)

= AUC oral/AUC IV