Exam 1: Pharmacokinetics

Question 1

Describe zero-order elimination and absorptive processes

Answer 1

Removes a constant amount of drug (remove 1000 each time) Constant amount of drug absorbed
Saturated process

Question 2

Describe first-order elimination and absorptive processes

Answer 2

Constant proportion of drug removes (remove 10% each time)

Constant proportion of drug absorbed

Question 3

What is dose proportionality?

Answer 3

Occurs when first-order processes exist and, as such, a change in dose results in a proportional change in plasma concentration
2x increase in does— 2x increase in plasma concentration

Question 4

Under what circumstances might dose proportionality not exist?

Answer 4

Saturation (zero-order) of absorptive process
–2x increase in dose—1.5x increase in plasma concentration
Saturation (zero-order) of elimination processes leading to drug accumulation beyond proportionality
–2x increase in dose— 3x increase in plasma concentrations

Question 5

What does it mean when a drug is said to have “flip‐flop” kinetics?

Answer 5

Occurs when the absorption rate is slower than the elimination rate. That is, the absorption rate constant primarily determines terminal drug concentrations

Question 6

What is an elimination half‐life and how can it be used to estimate the time required to eliminate a drug?

Answer 6

An elimination half-life is the time it takes for the body to remove ½ of the drug present
Zero order processes: half-life changes with changing drug concentrations
First order processes: half-life is constant

Question 7

What is the purpose in pharmacokinetics of a volume of distribution (Vd) term?

Answer 7

It lists the volume per unit weight

Question 8

Does Vd have physiologic significance?

Answer 8

Vd is a mathematical term that may or may not have physiologic significance

Question 9

Explain the Plateau principle (Steady-state)

Answer 9

When peak and trough concentrations do not vary between dosing intervals
Predicts how long you have to wait

Question 10

How does changing the dose affect time until steady-state?

Answer 10

Dosage changes result in differing peak and trough values, but it still takes the same amount of time to reach steady-state

Question 11

How does changing the dosing interval affect time until steady-state?

Answer 11

Dosage interval changes also results in differing peak and trough values, but it still takes the same amount of time to reach steady-state

Question 12

What is therapeutic drug monitoring (TDM)?

Answer 12

It individualizes a patient’s dosage regimen based on serum drug concentrations. It serves to improve efficacy and minimize toxicity
Electrolytes (bicarbonate) are an example of TDM usage

Question 13

Under what conditions is TDM typically used?

Answer 13

Pharmacokinetics of the drug are understood
Pharmacodynamics of the drug are understood
The drug has a low therapeutic index

Question 14

Under what conditions might a loading dose be needed?

Answer 14

When you need a drug with immediate onset and a long half-life

Question 15

Be able to calculate an adjusted maintenance dose using the Ratio (proportionality)” method. What conditions (assumptions) must be met to properly use this method of dose adjustment?

Answer 15

Old dose/existing concentration = new dose/desired concentration
Conditions/assumptions:
No change in interval will occur
Kinetic processes are all first-order. That is, dose proportionality exists

Question 16

Why is Total Body Clearance (CL) the best parameter for describing the overall disposition of a drug, and what kinetic parameters is it calculated from?

Answer 16

It is the best parameter because it addresses both the elimination rate and the Vd
It is calculated from the rate of elimination, Vd, and half-life