Which antiemetic is contraindicated in patients with angle-closure glaucoma?

Scopolamine is an anticholinergic medication commonly used to prevent nausea and vomiting, particularly in motion sickness. Its mechanism involves blocking the action of acetylcholine in the vestibular system and the vomiting center in the brain. One of the significant side effects of anticholinergic agents like scopolamine is their ability to dilate the pupils (mydriasis), which can lead to increased intraocular pressure. This poses a particular risk in patients with angle-closure glaucoma, a condition where the drainage angle is blocked, and increased pressure can lead to damage to the optic nerve and potential loss of vision.

In patients who have a history of angle-closure glaucoma or are at risk for it, the use of scopolamine can worsen their condition due to its pharmacological properties. Therefore, it is contraindicated in this patient population to prevent complications associated with elevated intraocular pressure.

The other options do not have the same contraindication. Dopamine antagonists, ondansetron, and metoclopramide act through different mechanisms and do not typically impact intraocular pressure in a manner that would exacerbate angle-closure glaucoma. Thus, scopolamine is specifically contraindicated in these patients due to its anticholinergic effects,