Chemotherapy: once-daily aminoglycoside dosing: practice question

A Pharmacology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Pharmacology · Chemotherapy: once-daily aminoglycoside dosing

Sample item

Why is gentamicin often given as a single large daily dose rather than in divided doses?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Killing is concentration dependent with a post-antibiotic effect, and renal cortical uptake saturates at high peaks

Aminoglycosides show concentration-dependent bactericidal activity and a prolonged post-antibiotic effect, so a high peak to MIC ratio is the goal. Uptake into proximal tubular cells and the inner ear is saturable, so a high single dose with a long trough interval reduces toxicity. It is not suitable in enterococcal endocarditis for synergy, in pregnancy, or in severe renal failure.

Option by option

  • A. Killing is concentration dependent with a post-antibiotic effect, and renal cortical uptake saturates at high peaks (correct)

    Correct. High peaks maximise killing, and the drug-free trough lowers renal uptake and toxicity.

  • B. Its half-life exceeds 24 hours, so daily dosing is the only way to avoid accumulation

    The half-life of gentamicin is only 2 to 3 hours in normal renal function.

  • C. The drug is bacteriostatic, so continuous low levels are needed

    Aminoglycosides are bactericidal.

  • D. Killing is time dependent and needs concentrations above MIC for the whole day

    Time-dependent killing describes beta-lactams, not aminoglycosides.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is A, Killing is concentration dependent with a post-antibiotic effect, and renal cortical uptake saturates at high peaks. Aminoglycosides show concentration-dependent bactericidal activity and a prolonged post-antibiotic effect, so a high peak to MIC ratio is the goal.

Why is "Its half-life exceeds 24 hours, so daily dosing is the only way to av…" not the answer?

The half-life of gentamicin is only 2 to 3 hours in normal renal function.

Why is "The drug is bacteriostatic, so continuous low levels are needed" not the answer?

Aminoglycosides are bactericidal.

Why is "Killing is time dependent and needs concentrations above MIC for the…" not the answer?

Time-dependent killing describes beta-lactams, not aminoglycosides.

What concept does this question test?

It tests Chemotherapy: once-daily aminoglycoside dosing in Pharmacology. Uptake into proximal tubular cells and the inner ear is saturable, so a high single dose with a long trough interval reduces toxicity. It is not suitable in enterococcal endocarditis for synergy, in pregnancy, or in severe renal failure.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Chemotherapy: once-daily aminoglycoside dosing?

Learn drugs as classes, then the exception in each class that an examiner would pick. Then use the flashcards and the other Pharmacology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.