GAMSAT Pharmacology Fundamentals 2

Question 1

A drug has a therapeutic index (TI) of 2. Which statement best describes this drug?

Accepted Answer

The toxic dose is twice the effective dose, indicating a narrow safety margin

Answer

A TI of 2 means the toxic dose (TD50) is only twice the effective dose (ED50), indicating a narrow safety window and higher risk of toxicity.

Question 2

Which pharmacokinetic process is primarily responsible for the first-pass effect?

Accepted Answer

Hepatic metabolism of orally absorbed drug before it reaches systemic circulation

Answer

The first-pass effect occurs when orally absorbed drugs pass through the portal circulation to the liver, where hepatic enzymes metabolise a significant fraction before the drug reaches systemic circulation.

Question 3

An antagonist is described as 'competitive' and 'surmountable.' What does this mean?

Accepted Answer

Increasing agonist concentration can overcome the blockade and restore the maximal response

Answer

A competitive surmountable antagonist reversibly binds the same receptor site as the agonist; increasing agonist concentration shifts the dose-response curve right but the same Emax is achievable.

Question 4

Which cytochrome P450 enzyme is most commonly responsible for drug-drug interactions in clinical practice?

Accepted Answer

CYP3A4

Answer

CYP3A4 metabolises approximately 50% of all marketed drugs, making it the most clinically significant isoenzyme for drug-drug interactions.

Question 5

A patient takes Drug X (a CYP2D6 substrate) with Drug Y (a potent CYP2D6 inhibitor). What is the most likely outcome?

Accepted Answer

Elevated plasma levels of Drug X due to decreased metabolism

Answer

Inhibiting CYP2D6 reduces the metabolism of Drug X, leading to higher plasma concentrations and potential toxicity.

(GAMSAT) Graduate Medical School Admissions Test Practice Test

(GAMSAT) Graduate Medical School Admissions Test Practice Test

GAMSAT Pharmacology Fundamentals 2