Question

A patient with vomiting was treated with an anti-emetic drug. The patient was relieved of vomiting but developed abnormal involuntary movements. What drug should be given to manage these abnormal movements?

• A. Methyl dopa
• B. Benzhexol
• C. Hyoscine
• D. Cyproheptadine

Hint:

The anti-emetic caused dopamine blockade -- think about which drug restores the dopamine-acetylcholine balance in the striatum.

Answer 1

The Correct Option is B

Step 1: Identify the cause of abnormal movements. Anti-emetics that act as dopamine D2 receptor antagonists (e.g., metoclopramide, domperidone, prochlorperazine) can cause extrapyramidal side effects (EPS), particularly acute dystonia and drug-induced parkinsonism, due to dopamine blockade in the nigrostriatal pathway.

Step 2: Classification of the abnormal movements. The abnormal involuntary movements following anti-emetic use are extrapyramidal in nature -- specifically acute dystonic reactions or drug-induced parkinsonism.

Step 3: Treatment of drug-induced extrapyramidal symptoms. Benzhexol (trihexyphenidyl) is an anticholinergic (antimuscarinic) drug. It restores the dopamine-acetylcholine balance in the striatum by blocking muscarinic receptors, thereby treating EPS caused by dopamine antagonists. It is approved for drug-induced parkinsonism and acute dystonia.

Step 4: Exclusion of other options. Methyl dopa is an antihypertensive that itself can cause EPS. Hyoscine is an anticholinergic used for motion sickness and spasms but is not the first choice for drug-induced EPS. Cyproheptadine is an antihistamine/antiserotonin drug with no role in EPS management.

Conclusion: Benzhexol (trihexyphenidyl) is given to treat abnormal movements (EPS) caused by anti-emetic dopamine antagonists.