DHA Pharmacist Pharmacokinetics and Pharmacodynamics 2

Question 1

A patient requires a loading dose of gentamicin. The target plasma concentration is 8 mg/L and the volume of distribution is 0.25 L/kg. For a 60 kg patient, what is the loading dose?

Accepted Answer

120 mg

Answer

Loading dose = Vd × target concentration = (0.25 × 60) × 8 = 15 × 8 = 120 mg.

Question 2

Phenytoin exhibits zero-order (saturation) kinetics at therapeutic doses. What clinical implication does this have?

Accepted Answer

Small dose increases can cause disproportionately large rises in plasma concentration

Answer

At saturation kinetics, elimination capacity is at maximum; small dose increases cannot be metabolized faster, causing disproportionate plasma level rises and toxicity risk.

Question 3

A drug is 95% bound to plasma proteins. Which statement best describes the pharmacokinetic consequence?

Accepted Answer

Only the 5% unbound fraction is pharmacologically active

Answer

Only the unbound (free) fraction can interact with receptors, cross membranes, and be eliminated; the protein-bound portion acts as an inactive reservoir.

Question 4

Creatinine clearance (CrCl) is used in clinical practice primarily to:

Accepted Answer

Adjust doses of renally eliminated drugs

Answer

CrCl estimates glomerular filtration rate (GFR) and is used to adjust doses of drugs that are primarily eliminated unchanged by the kidneys.

Question 5

CYP3A4 is the most abundant hepatic CYP450 enzyme. A drug that strongly inhibits CYP3A4 (e.g., ketoconazole) will most likely:

Accepted Answer

Increase plasma levels of CYP3A4 substrates

Answer

Inhibiting CYP3A4 reduces metabolism of its substrates, causing drug accumulation and increased plasma concentrations, which may lead to toxicity.

DHA Pharmacist Practice Test

DHA Pharmacist Practice Test

DHA Pharmacist Pharmacokinetics and Pharmacodynamics 2