Pharmacology Pharmacokinetics and Drug Metabolism 2

Question 1

A drug with a high extraction ratio is administered orally. Which phenomenon most significantly reduces its systemic bioavailability?

Accepted Answer

First-pass metabolism

Answer

High-extraction-ratio drugs are extensively metabolized by the liver on first pass, greatly reducing the fraction that reaches systemic circulation.

Question 2

Which cytochrome P450 isoform is responsible for metabolizing approximately 50% of all clinically used drugs?

Accepted Answer

CYP3A4

Answer

CYP3A4 is the most abundant hepatic CYP enzyme and metabolizes roughly half of all drugs in clinical use.

Question 3

A patient taking rifampin begins a new medication. The new drug's plasma levels are unexpectedly low. What is the most likely explanation?

Accepted Answer

Rifampin induces CYP450 enzymes

Answer

Rifampin is a potent CYP450 inducer that increases metabolism of co-administered drugs, lowering their plasma concentrations.

Question 4

What is the clinical significance of a drug having a large volume of distribution (Vd)?

Accepted Answer

The drug distributes extensively into tissues

Answer

A large Vd indicates that the drug distributes widely into peripheral tissues rather than remaining in the plasma compartment.

Question 5

Which phase II metabolic reaction conjugates drugs with glucuronic acid?

Accepted Answer

Glucuronidation

Answer

Glucuronidation, catalyzed by UDP-glucuronosyltransferases, is the most common phase II conjugation reaction that enhances water solubility.

Pharmacology Practice Test