Pharmokinetics II

Question 1

Can the loading dose change the time it takes to reach the steady state?

Answer 1

NO.

Question 2

What is the loading dose?

Answer 2

It is a “start-up” dose that is used to reach the therapeutic level more rapidly.

Question 3

What is the primary determinant of the maintenance dose?

Answer 3

Clearance

Question 4

What is the target for the loading dose?

Answer 4

The peak therapeutic concentration

Question 5

What is elimination clearance?

Answer 5

Irreversible drug removal from the plasma through an eliminating organ(s).

Question 6

Do higher doses achieve the steady state faster?

Answer 6

No

Question 7

What is 1st order elimination?

Answer 7

The elimination rate of the drug is a constant fraction of the drug remaining in the body

Question 8

What is 0 order elimination?

Answer 8

A fixed amount of drug is metabolized per unit time

Question 9

What are some drugs that follow 1st order elimination?

Answer 9

Most clinical drugs do

Question 10

What are some drugs that follow 0 order elimination?

Answer 10

Ethanol

Phenytoin

Question 11

What is dose dependent elimination?

Answer 11

It is 1st order if Km far greater than C and 0 order if Km far less than C

Question 12

A patient with grand mal seizures is receiving phenytoin 300 mg po per day. The phenytoin plasma level is 9.5 􏰀g/ml (therapeutic range 10-20 􏰀g/ml). The dose of phenytoin is increased to 500 mg po per day and one week later the patient presents with lethargy and ataxia. A repeat phenytoin plasma level is now 30 􏰀g/ml. Which of the following best explains this clinical picture?

A) Phenytoin follows first-order kinetics of elimination.
B) The bioavailability of phenytoin has decreased.
C) Saturation of metabolic pathways resulted in toxic
levels.
D) The Vmax for phenytoin metabolism has increased.
E) The renal clearance of phenytoin has decreased.

Answer 12

C) Saturation of metabolic pathways resulted in toxic

levels.

Question 13

Which of the following is true when a drug exhibits zero-order kinetics of elimination?

A) A constant fraction of the drug is eliminated per unit time.
B) A constant fraction of the volume of distribution is cleared of drug.
C) A constant amount of drug is eliminated per unit time.
D) A constant half-life of elimination is observed.
E) A constant oral bioavailability is seen regardless of the dose.

Answer 13

C) A constant amount of drug is eliminated per unit time.

Question 14

Which of the following is considered a “primary” pharmacokinetic parameter?

A)The loading dose
B)The elimination half-life 
C)The elimination clearance 
D)The Vmax and the Km
E) The infusion rate

Answer 14

C) The elimination clearance

Question 15

What is the time to reach the steady state dependent upon?

Answer 15

The half life of the drug

Question 16

What are the primary pharmokinetic parameters?

Answer 16

Clearance (CL)

Volume of Distribution (Vd)

Question 17

Propranolol has a half-life of elimination (t1⁄2) of 4 hours and is prescribed to a patient at a dose of 20 mg orally every 6 hours. How long will it take to reach 90% of the steady-state plasma level with continuous therapy?

A. 6 hours 
B. 9 hours 
C. 13 hours 
D. 18 hours 
E. 26 hours

Answer 17

C. 13 hours

Question 18

In cases of renal insufficiency, how can the dose rate be adjusted?

Answer 18

• Reducing the dose

- Increasing the dosing interval

Question 19

What are the determinants of hepatic drug clearance?

Answer 19

1. Hepatic Blood Flow
   (Rate of drug delivery to the eliminating organ)
2. Plasma Protein Binding (Fraction of drug available for clearance)
3. Intrinsic Clearance
   (Hepatocellular metabolism and/or biliary excretion)

Question 20

What is the most important determinant in restrictive hepatic clearance?

Answer 20

Drug binding or drug metabolism/excretion

Question 21

What is the most important determinant in non-restrictive hepatic clearance?

Answer 21

Blood flow