Which drug class is contraindicated in narrow-angle glaucoma?

Decongestants are contraindicated in narrow-angle glaucoma due to their potential to increase intraocular pressure. This class of medications often includes agents that are sympathomimetic in nature, which means they can stimulate alpha-adrenergic receptors. The stimulation of these receptors can lead to dilated pupils (mydriasis) and can potentially block the exit of aqueous humor through the trabecular meshwork, thereby worsening the condition in patients with narrow-angle glaucoma.

In this condition, the angle between the iris and the cornea is already narrow, making it more difficult for the fluid within the eye to drain properly. By promoting pupil dilation and fluid buildup, decongestants can exacerbate the risk of an acute attack of glaucoma, which can lead to significant vision loss if not treated promptly. Other drug classes like expectorants, antitussives, and antihistamines do not have this direct mechanism of action that affects pupil size or intraocular pressure in the same way, making them safer alternatives for individuals with narrow-angle glaucoma.