Basic Pharmacokinetic Principles

Question 1

pharmacokinetics

Answer 1

the actions the body takes on a drug

can be defined in terms of volumes and clearances

Question 2

pharmacodynamics (PD)

Answer 2

the action a drug has on the body

Question 3

volume of distribution

Answer 3

that volume in which a substance/marker/drug appears to be homogeneously distributed (dissolved)

an apparent volume of distribution

volume of distribution = amount of substance/concentration

more accurately described as plasma equivalent apparent volume of distribution

Question 4

the hydraulic model

Answer 4

can be used to compare to drug distribution int he body

• water soluble substances travers aqueous channels between compartments

aqueous channels vary in size

Question 5

Describe the body’s water distribution.

Answer 5

Question 6

first law of pharmacokinetics

Answer 6

amount of drug in body = concentration * volume of distribution

Question 7

clearance

Answer 7

a term used to describe the time-dependent movement of drug

includes intercompartmental clearance and elimination clearance

rate of elimination = clearance * concentration

Question 8

intercompartmental clearance

Answer 8

describes the movement of drug between compartments

Question 9

elimination clearance

Answer 9

describes the metabolic alteration or removal of drug from the blood/body

rate constant (k) = clearance (liters/min)/volume(liters)

time constant (minutes) = volume (liters)/clearance(liters/min)

Question 10

elimination clearance rate constant

Answer 10

the fraction or percentage of the volume that is cleared per unit time (minutes)

T(1/2) = 0.693/k

Question 11

elimination clearance time constant

Answer 11

the time it takes for about 63% of the volume to be cleared

95% of a substance is cleared in three time constants

Question 12

extraction ration

Answer 12

extraction ratio = clearance/flow

Question 13

renal clearance

Answer 13

that part of the volume of distribution from which a substance is irreversibly removed

creatinine clearance = (U x V)/P

U = concentration of creatinine in the urine

V = time measured collection of urine (urine production rate)

P = concentration of creatinine in the plasma

Question 14

second law of pharmacokinetics

Answer 14

target (steady state) concentration = infusion rate/clearance

Question 15

clearance vs. elimination rate

Answer 15

clearance is a physiologic process assumed not to change over the course of observation

elimination rate is constantly changing due to the concentration of the parent drug constantly decreasing as a result of drug being continuously eliminiated from the system