Drug Metabolism

Question 1

Volume of Distribution

Answer 1

Vd= Amt of Drug in Body/ Plasma Drug Concentration

Question 2

Clearance

Answer 2

CL= Rate of Drug Elimination/ Plasma Drug Conc

CL= CLrenal + CLhepatic + CLother

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

Question 3

Half Life

Answer 3

t1/2=( 0.693xVd)/ CL

**Only for drugs that follow first order kinetics

Question 4

Dosing Rate for Maintenance Dose

Answer 4

(CL x Desired Plasma Conc)/ Bioavailability

• **F= Bioavailability
• **Css= Desired Plasma Conc
• **Note that Vd is not involved in this calculation

Question 5

Loading Dose

**If therapeutic dose must be achieved very rapidly

Answer 5

(Vd x Desired Plasma Conc)/ Bioavailability

• **F= Bioavailability
• **Css= Desired Plasma Conc

Question 6

Michaelis- Menton Kinetics Equation

Answer 6

V= (Vmax[S]) / (Km + [S])

Question 7

Rate of elimination of an organ

Answer 7

Q x (Ca-Cv) where Q is the blood flow to the organ

Question 8

Extraction Rate (E)

Answer 8

E= [(Ca-Cv)/Ca]

Question 9

Steady State

Answer 9

Css= (F x Dose)/ CL x T

Question 10

What drugs exhibit zero order kinetics?

Answer 10

1. Ethanol
2. Heparin
3. Phenytoin
4. Aspirin
5. Amobarbital
6. Tetracycline

Question 11

Equations for Zero Order Kinetics

Answer 11

LD= (Vd x Css)/ F

Css= (Km x DR)/ (Vm-DR)

DR= (Css x (Vm-DR))/ Km

***Km= dose that produces 50% of the max elimination rate

Question 12

For IV Infusion:

Answer 12

Css= infusion rate/ total body clearance

Question 13

Constant Infusion Principle

Answer 13

States that one half life is required to reach one half of the final concentration.

Question 14

How is biotransformation most likely to change a drug?

Answer 14

IT usually produces a drug that is less lipid soluble.