antimuscarinic

An antimuscarinic, or anticholinergic agent, is a drug that blocks muscarinic acetylcholine receptors (M1–M5), inhibiting parasympathetic nerve activity. They act as competitive antagonists at these G protein–coupled receptors, thereby diminishing glandular secretions, relaxing smooth muscle, increasing heart rate, and affecting central nervous system function depending on blood-brain barrier penetration.

Pharmacologic effects include dry mouth, blurred vision with cycloplegia, photophobia, urinary retention, constipation, tachycardia, decreased sweating and heat dissipation, bronchodilation, and, with central penetration, confusion or delirium in susceptible individuals. Peripheral agents with minimal CNS effects (like ipratropium, tiotropium, glycopyrrolate, oxybutynin) are designed for targeted uses, while scopolamine and some hydrophobic agents readily affect cognition.

Common clinical uses include treatment of bradyarrhythmias, preoperative reduction of secretions, and antidotal therapy for anticholinesterase poisoning. Inhaled antimuscarinics such as ipratropium and tiotropium relieve bronchospasm in COPD and asthma. Overactive bladder is treated with tolterodine, oxybutynin, solifenacin, darifenacin, and trospium. Antimuscarinics such as benztropine and trihexyphenidyl help manage drug-induced parkinsonism and extrapyramidal symptoms.

Adverse effects include dry mouth, constipation, urinary retention, blurred vision, tachycardia, confusion, and delirium, particularly in older adults. They can worsen glaucoma (especially narrow-angle) and should be used with caution in BPH and myasthenia gravis. Because many antimuscarinics contribute to overall anticholinergic burden, elderly patients are at higher risk of cognitive impairment, delirium, and falls, especially with multiple interacting medications.