Antiepileptics: intravenous phenytoin: 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 · Antiepileptics: intravenous phenytoin

Sample item

Intravenous phenytoin during status epilepticus must be infused slowly, at no more than 50 mg per minute in adults. What is the main reason?

ARespiratory depression through GABA enhancementBAcute hepatic necrosis from rapid loadingCSevere hypoglycaemia from insulin releaseDCardiac arrhythmias and hypotension, partly due to the propylene glycol vehicle

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

The answer and the reasoning

D. Cardiac arrhythmias and hypotension, partly due to the propylene glycol vehicle

Rapid intravenous phenytoin causes bradycardia, conduction block and hypotension, attributed to the drug and its propylene glycol and alcohol vehicle. ECG and blood pressure are monitored during loading. Fosphenytoin, a water-soluble prodrug, can be infused faster with fewer local reactions.

Option by option

A. Respiratory depression through GABA enhancement
Phenytoin blocks sodium channels and has little effect on GABA or respiratory drive.
B. Acute hepatic necrosis from rapid loading
Hepatotoxicity from phenytoin is idiosyncratic and not related to infusion speed.
C. Severe hypoglycaemia from insulin release
Phenytoin tends to inhibit insulin release and cause hyperglycaemia, not hypoglycaemia.
D. Cardiac arrhythmias and hypotension, partly due to the propylene glycol vehicle (correct)
Rapid infusion can cause hypotension and arrhythmia, so the rate is capped and the ECG monitored.

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 D, Cardiac arrhythmias and hypotension, partly due to the propylene glycol vehicle. Rapid intravenous phenytoin causes bradycardia, conduction block and hypotension, attributed to the drug and its propylene glycol and alcohol vehicle.

Why is "Respiratory depression through GABA enhancement" not the answer?

Phenytoin blocks sodium channels and has little effect on GABA or respiratory drive.

Why is "Acute hepatic necrosis from rapid loading" not the answer?

Hepatotoxicity from phenytoin is idiosyncratic and not related to infusion speed.

Why is "Severe hypoglycaemia from insulin release" not the answer?

Phenytoin tends to inhibit insulin release and cause hyperglycaemia, not hypoglycaemia.

What concept does this question test?

It tests Antiepileptics: intravenous phenytoin in Pharmacology. ECG and blood pressure are monitored during loading. Fosphenytoin, a water-soluble prodrug, can be infused faster with fewer local reactions.

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 Antiepileptics: intravenous phenytoin?

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.