Pharmacokinetics 1

Question 1

What is clearance?

Answer 1

body’s efficiency of drug removal. Theroretical volume of fluid from which a drug is removed per unit time.
CL = rate of elimination/concentration

Question 2

What is volume of distribution?

Answer 2

apparent space the drug resides in. Fluid volume that would be required to contain all of the dose at the same concentration as exists in the blood or plasma.
Vd = amount of drug in body/ C
where C is blood concentration

Question 3

What is elimination half-life?

Answer 3

rate of drug removal

Question 4

What is bioavailability?

Answer 4

fraction of drug absorbed

Question 5

What is the most important concept to be considered when a rational regimen for long-term drug administration is to be designed?

Answer 5

Clearance

Question 6

What is the formula for dosing rate for long-term administered drugs?

Answer 6

Dosing rate = CL x Css (where CL is clearance and Css is steady-state concentration of drug

Question 7

What is formula for rate of elimination of an organ?

Answer 7

Rate of elimination of organ = Q(Ca-Cv), where Q = blood flow to organ

Question 8

What is the formula for clearance in terms of Ca and Cv?

Answer 8

CL = Q[(Ca-Cv)/Ca] = Q x E

Where E is the extraction ratio

Question 9

What is the limiting variable for elimination from any organ?

Answer 9

blood flow, Q

Question 10

What type of kinetic mode do most drugs eliminate by?

Answer 10

First order kinetics

Question 11

What is formula for volume of distribution?

Answer 11

Vd = amount of drug in body/blood concentration

blood concentration = C

Question 12

What is average total body water? Plasma volume? Extracellular fluid volume? Intracellular fluid?

Answer 12

Total = 40 L
Plasma = 4 L
Extracellular = 12 L
Intracellular = 28L

Question 13

What is Ke?

Answer 13

elimination constant = CL/Vd

Question 14

What is the formula for half-life for zero order kinetic drug?

Answer 14

t1/2 = 0.7/Ke = 0.7xVd/CL

Question 15

Why is half-life clinically important?

Answer 15

Helps determine the dosing interval (drugs are usually given at half-life intervals).
May determine route of administration (short half-lifes are usually given by IV or sustained release patches or tablets)
Provides good indication of time required to reach steady-state after a dosage regimen is initiated. Assumes one elimination rate (excretion)

Question 16

What is the one-compartment model? What type of drugs is it acceptable for?

Answer 16

Assumes the entire human body is one compartment. This works for drugs that are distributed uniformly throughout the body

Question 17

What is the two-compartment model?

Answer 17

Assumes that much of a drug is in a particular compartment and that an equilibrium exists between the blood and other areas. Have two different elimination rates (excretion and transfer rate between blood and compartment)

Question 18

What type of model is most accurate for human body?

Answer 18

Multicompartment models. Requires use of computer to model, but is more widely used than one and two-compartment models.
CL = dose/AUC
AUC = area under curve

Question 19

What is the equation to factor bioavailability into the dosing rate?

Answer 19

FxDosing rate = CL x Css

Question 20

Taking bioavailability into account, what is formula to calculate steady state concentration?

Answer 20

Css = (FxDose)/(CLxT)
Where Dosing rate = Dose/T
T = dosing interval

Question 21

Taking bioavailability into account, what is equation to calculate Dose?

Answer 21

Dose = (Css x CL x T)/F

Question 22

About how long does it take to achieve steady state?

Answer 22

Usually takes about 5 half-lives to achieve steady state

Question 23

What is time to steady-state strictly dependent on?

Answer 23

half life.

This is the plateau principle