antimuscarinics

Antimuscarinics are a class of drugs that act as antagonists of muscarinic acetylcholine receptors, thereby blocking parasympathetic nerve signals. They produce their effects by competitively inhibiting M1–M5 receptor subtypes, with tissue distribution largely determining the clinical outcome. Some agents are lipophilic tertiary amines (for example atropine and scopolamine) that can cross the blood–brain barrier and cause central effects; others are quaternary ammonium compounds (such as glycopyrrolate and ipratropium) with limited CNS penetration and largely peripheral actions.

Clinical uses span several systems. In ophthalmology they cause mydriasis and cycloplegia. In anesthesia, antimuscarinics reduce secretions and help prevent bradycardia. In the GI tract they decrease motility and secretions, and in the urinary tract they reduce detrusor muscle contractions to treat overactive bladder. In respiratory medicine, inhaled agents like ipratropium and tiotropium produce bronchodilation. Some are used to treat extrapyramidal symptoms of Parkinsonism or antipsychotic-induced dystonia. Scopolamine is employed for motion sickness and postoperative nausea.

Common agents include atropine, scopolamine, glycopyrrolate, ipratropium, tiotropium, and urinary antimuscarinics such as oxybutynin, tolterodine, solifenacin, darifenacin, and trospium. The therapeutic choice often reflects the balance between desired organ-system effects and anticholinergic burden.

Adverse effects arise from anticholinergic blockade: dry mouth, blurred vision, constipation, urinary retention, tachycardia, and, especially in older adults, cognitive impairment or delirium. Contraindications include angle-closure glaucoma, urinary retention, certain types of intestinal obstruction, and significant myasthenia gravis; caution is advised with polypharmacy and in the elderly.