Pharmacokinetics: ion trapping and excretion: 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 · Pharmacokinetics: ion trapping and excretion

Sample item

A 20-year-old woman presents with tinnitus, fast deep breathing and vomiting after taking many aspirin tablets. Which measure enhances renal elimination of the drug?

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

The answer and the reasoning

B. Intravenous sodium bicarbonate to alkalinise the urine

Salicylic acid is a weak acid. In alkaline urine it is mostly ionised, cannot cross tubular epithelium back into blood and is trapped in the urine (ion trapping). Alkalinisation also keeps salicylate out of the brain. Acidifying urine would favour excretion of weak bases such as amphetamine.

Option by option

  • A. Furosemide alone to produce forced diuresis

    Forced diuresis without alkalinisation adds little and risks fluid and electrolyte disturbance.

  • B. Intravenous sodium bicarbonate to alkalinise the urine (correct)

    Correct. Alkaline urine ionises the weak acid and prevents its tubular reabsorption.

  • C. Ammonium chloride to acidify the urine

    Acidifying the urine would make salicylate non-ionised and reabsorbed, and worsens acidosis.

  • D. Fomepizole to block drug metabolism

    Fomepizole inhibits alcohol dehydrogenase and is used in methanol or ethylene glycol poisoning.

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.

More Pharmacology questions

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is B, Intravenous sodium bicarbonate to alkalinise the urine. Salicylic acid is a weak acid.

Why is "Furosemide alone to produce forced diuresis" not the answer?

Forced diuresis without alkalinisation adds little and risks fluid and electrolyte disturbance.

Why is "Ammonium chloride to acidify the urine" not the answer?

Acidifying the urine would make salicylate non-ionised and reabsorbed, and worsens acidosis.

Why is "Fomepizole to block drug metabolism" not the answer?

Fomepizole inhibits alcohol dehydrogenase and is used in methanol or ethylene glycol poisoning.

What concept does this question test?

It tests Pharmacokinetics: ion trapping and excretion in Pharmacology. In alkaline urine it is mostly ionised, cannot cross tubular epithelium back into blood and is trapped in the urine (ion trapping). Alkalinisation also keeps salicylate out of the brain. Acidifying urine would favour excretion of weak bases such as amphetamine.

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 Pharmacokinetics: ion trapping and excretion?

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.