Toxicology: mercury: 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 · Toxicology: mercury

Sample item

A worker exposed to methylmercury in contaminated fish has paraesthesia, ataxia and constriction of visual fields. A trainee proposes intramuscular dimercaprol. Why is this inappropriate?

AIt can redistribute mercury into the brain, and organic mercury is better treated with succimerBIt is only active against leadCIt converts methylmercury to inorganic mercury in the kidneyDIt binds mercury too weakly to promote excretion

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

The answer and the reasoning

A. It can redistribute mercury into the brain, and organic mercury is better treated with succimer

Methylmercury is lipophilic and concentrates in the nervous system. Dimercaprol forms lipid-soluble complexes with mercury and can increase brain levels of organic mercury, so it is avoided. Oral succimer or DMPS, which are water soluble, are preferred, and dimercaprol is reserved for acute inorganic mercury salt poisoning.

Option by option

A. It can redistribute mercury into the brain, and organic mercury is better treated with succimer (correct)
Dimercaprol can move organic mercury into the brain, so water-soluble chelators are used.
B. It is only active against lead
Dimercaprol acts against arsenic, mercury and gold, and not only lead.
C. It converts methylmercury to inorganic mercury in the kidney
Chelators do not change the chemical form of mercury in the kidney.
D. It binds mercury too weakly to promote excretion
Dimercaprol binds mercury avidly through its thiol groups.

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, It can redistribute mercury into the brain, and organic mercury is better treated with succimer. Methylmercury is lipophilic and concentrates in the nervous system.

Why is "It is only active against lead" not the answer?

Dimercaprol acts against arsenic, mercury and gold, and not only lead.

Why is "It converts methylmercury to inorganic mercury in the kidney" not the answer?

Chelators do not change the chemical form of mercury in the kidney.

Why is "It binds mercury too weakly to promote excretion" not the answer?

Dimercaprol binds mercury avidly through its thiol groups.

What concept does this question test?

It tests Toxicology: mercury in Pharmacology. Dimercaprol forms lipid-soluble complexes with mercury and can increase brain levels of organic mercury, so it is avoided. Oral succimer or DMPS, which are water soluble, are preferred, and dimercaprol is reserved for acute inorganic mercury salt poisoning.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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: mercury?

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.