Pharmacokinetics/dynamics

Question 1

How do competitive and noncompetitive inhibitors impact potency? efficacy?

Answer 1

Competitive decreases potency (need more drug to have the same effect)

Noncompetitive decreases efficacy (decrease the number of enzymes available by changing the shape)

Question 2

What is Km related to?

Answer 2

Inversely related to the affinity of the enzyme for its substrate

Question 3

What is Vmax related to?

Answer 3

Directly proportional to the enzyme concentration (“can you get the same response?”)

Question 4

Calculation: Volume of distribution

Answer 4

Vd = (amount of drug in the body) / (plasma drug concentration)

Question 5

Calculation: t 1/2

Answer 5

(0.7 x Vd) / (CL)

Question 6

How many half-lives does it take to reach steady state?

Answer 6

4-5

Question 7

Equation: Clearance

Answer 7

CL = rate of elimination of a drug/plasma drug concentration

CL = Vd x Ke (elimination constant)

Question 8

Calculation: Loading dose

Answer 8

(Cp x Vd) / (F)

*Cp = target plasma concentration at ss

Question 9

Calculation: Maintenance dose

Answer 9

(Cp x CL x time between doses) / (F)

*Cp = target plasma concentration at ss

Question 10

Zero order elimination drugs

Answer 10

Phenytoin
Ethanol
Aspirin

Question 11

Zero-order elimination

Answer 11

A constant amount of the drug is eliminated per unit time regardless of Cp

Question 12

First-order elimination

Answer 12

A constant fraction of the drug is eliminated per unit time - directly proportional to the drug concentration

Question 13

Ionized vs. unionized solubility

which is water soluble? lipid soluble?

Answer 13

Ionized = water soluble
Unionized = lipid soluble

Question 14

What phase of metabolism do geriatric patients lose?

Answer 14

Phase I

Question 15

Calculation: Therapeutic index

Answer 15

TD50/ED50 (toxic dose over effective dose)

*higher equals safer