Pharmacology Pharmacokinetics and Drug Metabolism Questions and Answers 1

Question 1

A patient is being treated with a drug that is a known substrate for the CYP3A4 enzyme. If the patient starts taking a new medication that is a potent inducer of CYP3A4, what is the most likely pharmacokinetic consequence?

Accepted Answer

Decreased plasma concentration of the first drug, leading to potential therapeutic failure.

Answer

CYP3A4 inducers increase the metabolic activity of the enzyme. This leads to a faster breakdown of the substrate drug, resulting in lower plasma concentrations and potentially reducing its therapeutic effect. [20, 28]

Question 2

A 500 mg dose of a drug is administered intravenously, resulting in an initial plasma concentration of 25 mg/L. What is the apparent volume of distribution (Vd) for this drug?

Accepted Answer

20 L

Answer

The volume of distribution (Vd) is calculated by dividing the dose administered by the initial plasma concentration (Vd = Dose / C0). In this case, Vd = 500 mg / 25 mg/L = 20 L. [26]

Question 3

Which of the following statements accurately describes Phase II metabolism?

Accepted Answer

It involves conjugation reactions that increase the water solubility of a drug for excretion. [7]

Answer

Phase II metabolism involves conjugation reactions, where an endogenous substrate (like glucuronic acid, sulfate, or an amino acid) is attached to the drug or its Phase I metabolite. This process generally increases the molecule's polarity and water solubility, facilitating its renal or biliary excretion. [1, 7]

Question 4

A patient with severe liver cirrhosis is administered a drug that is primarily eliminated through hepatic metabolism. How would this patient's condition most likely affect the drug's half-life (t1/2)?

Accepted Answer

The half-life will be significantly prolonged. [3]

Answer

Liver cirrhosis impairs the liver's metabolic capacity. Since the drug is primarily eliminated by the liver, its clearance will be reduced. A decrease in clearance leads to a prolongation of the elimination half-life, increasing the risk of drug accumulation and toxicity. [3, 15]

Question 5

The 'first-pass effect' primarily refers to the pre-systemic metabolism of an orally administered drug that occurs in which two organs?

Accepted Answer

Liver and small intestine [13, 18]

Answer

The first-pass effect, or first-pass metabolism, describes the process where a drug administered orally is absorbed from the gastrointestinal tract and transported via the portal vein to the liver. Both the intestinal wall and the liver contain enzymes that can metabolize the drug before it reaches systemic circulation, thereby reducing its bioavailability. [5, 13, 18]

Pharmacology Practice Test

Pharmacology Practice Test

Pharmacology Pharmacokinetics and Drug Metabolism Questions and Answers 1