Antidiabetic drugs: metformin adverse effects: 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 · Antidiabetic drugs: metformin adverse effects

Sample item

A 62-year-old man with type 2 diabetes on metformin for ten years has macrocytic anaemia and paraesthesia of the feet. Which adverse effect of the drug explains this?

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

The answer and the reasoning

A. Impaired ileal absorption of vitamin B12

Long-term metformin lowers vitamin B12 absorption, probably by interfering with calcium-dependent uptake of the intrinsic factor complex in the terminal ileum. Deficiency may cause macrocytic anaemia and neuropathy, and periodic monitoring is advised in long-term users. This can be mistaken for diabetic neuropathy.

Option by option

  • A. Impaired ileal absorption of vitamin B12 (correct)

    Correct. Metformin impairs B12 uptake in the ileum with long-term use.

  • B. Inhibition of dihydrofolate reductase

    Inhibition of dihydrofolate reductase is the effect of methotrexate and trimethoprim.

  • C. Chronic gastrointestinal blood loss causing iron deficiency

    Iron deficiency would cause microcytosis and metformin does not cause occult bleeding.

  • D. Pyridoxine antagonism

    Pyridoxine antagonism is seen with isoniazid, not metformin.

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, Impaired ileal absorption of vitamin B12. Long-term metformin lowers vitamin B12 absorption, probably by interfering with calcium-dependent uptake of the intrinsic factor complex in the terminal ileum.

Why is "Inhibition of dihydrofolate reductase" not the answer?

Inhibition of dihydrofolate reductase is the effect of methotrexate and trimethoprim.

Why is "Chronic gastrointestinal blood loss causing iron deficiency" not the answer?

Iron deficiency would cause microcytosis and metformin does not cause occult bleeding.

Why is "Pyridoxine antagonism" not the answer?

Pyridoxine antagonism is seen with isoniazid, not metformin.

What concept does this question test?

It tests Antidiabetic drugs: metformin adverse effects in Pharmacology. Deficiency may cause macrocytic anaemia and neuropathy, and periodic monitoring is advised in long-term users. This can be mistaken for diabetic neuropathy.

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 Antidiabetic drugs: metformin adverse effects?

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.