Toxicology: metformin toxicity: practice question

A Forensic Medicine 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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Forensic Medicine · Toxicology: metformin toxicity

Sample item

An elderly man with chronic kidney disease takes a large overdose of metformin and has hyperventilation and vomiting. Which acid-base picture is expected?

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

The answer and the reasoning

D. Anion gap metabolic acidosis from lactate

Metformin inhibits hepatic gluconeogenesis and mitochondrial respiration, so lactate accumulates, especially when renal clearance is reduced. The result is a high anion gap lactic acidosis, and haemodialysis is used in severe cases to remove both the drug and the lactate.

Option by option

  • A. Diabetic ketoacidosis with marked hyperglycaemia

    Metformin does not cause ketoacidosis or marked hyperglycaemia.

  • B. Respiratory alkalosis with hypokalaemia

    Respiratory alkalosis is a feature of early salicylate poisoning, not of metformin overdose.

  • C. Hyperchloraemic acidosis with a normal anion gap

    Hyperchloraemic acidosis has a normal anion gap, whereas lactic acidosis raises it.

  • D. Anion gap metabolic acidosis from lactate (correct)

    Correct. Lactate accumulation causes a high anion gap acidosis.

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 Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is D, Anion gap metabolic acidosis from lactate. Metformin inhibits hepatic gluconeogenesis and mitochondrial respiration, so lactate accumulates, especially when renal clearance is reduced.

Why is "Diabetic ketoacidosis with marked hyperglycaemia" not the answer?

Metformin does not cause ketoacidosis or marked hyperglycaemia.

Why is "Respiratory alkalosis with hypokalaemia" not the answer?

Respiratory alkalosis is a feature of early salicylate poisoning, not of metformin overdose.

Why is "Hyperchloraemic acidosis with a normal anion gap" not the answer?

Hyperchloraemic acidosis has a normal anion gap, whereas lactic acidosis raises it.

What concept does this question test?

It tests Toxicology: metformin toxicity in Forensic Medicine. The result is a high anion gap lactic acidosis, and haemodialysis is used in severe cases to remove both the drug and the lactate.

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 Toxicology: metformin toxicity?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine 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.