When updating an antimuscarinic prescribing policy, which condition would contraindicate its use?

• A. Urinary retention
• B. Hypertension
• C. Toxic megacolon
• D. Glaucoma

Answer: (C)

Antimuscarinic medicines block acetylcholine at muscarinic receptors, which lowers parasympathetic activity and reduces GI motility. In toxic megacolon, the colon is already severely distended and inflamed; further decreasing motility can worsen distension and raise the risk of perforation. That makes its use clearly unsafe in this situation.

Urinary retention can be worsened by these drugs, so caution is advised but it’s not an absolute contraindication in all cases. Glaucoma is a concern because antimuscarinics can raise intraocular pressure by dilating the pupil, especially in narrow-angle glaucoma, but the scenario of toxic megacolon represents a more definitive contraindication. Hypertension is not a primary contraindication.