General pharmacology and pharmacokinetics: dose in renal failure: 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.

Try it

Pharmacology · General pharmacology and pharmacokinetics: dose in renal failure

Sample item

A patient with an estimated creatinine clearance of 20 mL/min needs gentamicin. Almost all of the drug is excreted unchanged by the kidneys. What is the most appropriate adjustment?

ALengthen the dosing interval and monitor levelsBSwitch to a route with lower first-pass lossCShorten the dosing intervalDRaise the loading dose in proportion to the fall in clearance

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

The answer and the reasoning

A. Lengthen the dosing interval and monitor levels

Drugs cleared by the kidney accumulate when clearance falls. The maintenance dose is reduced or the interval extended, with drug levels monitored for narrow-margin drugs such as aminoglycosides. A loading dose depends on volume of distribution and is usually not changed.

Option by option

A. Lengthen the dosing interval and monitor levels (correct)
Correct. Reduced clearance needs a longer interval or a smaller dose, with levels followed.
B. Switch to a route with lower first-pass loss
Gentamicin is injected and has no first-pass loss to avoid.
C. Shorten the dosing interval
A shorter interval would accumulate drug and worsen nephrotoxicity and ototoxicity.
D. Raise the loading dose in proportion to the fall in clearance
Loading dose depends on volume of distribution, not on clearance.

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.

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is A, Lengthen the dosing interval and monitor levels. Drugs cleared by the kidney accumulate when clearance falls.

Why is "Switch to a route with lower first-pass loss" not the answer?

Gentamicin is injected and has no first-pass loss to avoid.

Why is "Shorten the dosing interval" not the answer?

A shorter interval would accumulate drug and worsen nephrotoxicity and ototoxicity.

Why is "Raise the loading dose in proportion to the fall in clearance" not the answer?

Loading dose depends on volume of distribution, not on clearance.

What concept does this question test?

It tests General pharmacology and pharmacokinetics: dose in renal failure in Pharmacology. The maintenance dose is reduced or the interval extended, with drug levels monitored for narrow-margin drugs such as aminoglycosides. A loading dose depends on volume of distribution and is usually not changed.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 General pharmacology and pharmacokinetics: dose in renal failure?

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.