USMLE Answer 8
8. The correct answer is A. There are three facts that are necessary to answer this question: what disease the patient is suffering from, what pharmacological properties can trigger an attack, and what drug has these pharmacological properties. The patient described is suffering from an attack of acute or narrow angle glaucoma. These attacks can be precipitated by drugs with anticholinergic actions because muscarinic receptors on the pupillary constrictor muscle of the iris are blocked. This causes pupillary dilation, which further “narrows” the angle in the anterior chamber of the eye. Amitriptyline is a tricyclic antidepressant with significant anticholinergic side effects.
Cimetidine (choice B) is an H2 antagonist that reduces gastric acid release. Its trade name is Tagamet and it is now available over the counter. It has no significant anticholinergic side effects.
Diazepam (choice C) is a benzodiazepine. Its trade name is Valium and it has no significant anticholinergic side effects.
Malathion (choice D) is an organophosphorus cholinesterase inhibitor that is used as an insecticide. This agent would increase levels of acetylcholine, thereby widening the angle.
Propranolol (choice E) is a non-seletive, beta-adrenergic antagonist. If anything, it would help to prevent an attack by blocking beta-receptors on the ciliary body, thereby diminishing aqueous humor production.