Antimuscarinica

Antimuscarinica, or antimuscarinic drugs, form a class of medications that block muscarinic acetylcholine receptors (M1–M5), thereby reducing the actions of the parasympathetic nervous system. They are used across several medical fields to counteract reflexes and secretions or to lessen smooth muscle tone, depending on the tissue targeted.

Mechanism and pharmacology: these agents act as competitive antagonists at muscarinic receptors. By inhibiting acetylcholine binding, they decrease glandular secretions, relax smooth muscle, and can increase heart rate by reducing vagal influence. Some agents cross the blood–brain barrier and may affect cognition, while others are quaternary ammonium compounds with minimal CNS penetration. Receptor subtype selectivity varies among drugs and influences clinical effects and side effects.

Common drugs and formulations include atropine and scopolamine (often used for preanesthetic medication and motion sickness), glycopyrrolate and ipratropium or tiotropium (often used for peptic ulcers or chronic obstructive pulmonary disease, with limited CNS effects for certain formulations), and a range of peripherally acting agents such as oxybutynin, tolterodine, solifenacin, and trospium for overactive bladder. In Parkinsonian syndromes, benztropine and trihexyphenidyl are used to reduce tremor and rigidity.

Clinical uses span ophthalmology (mydriasis and cycloplegia), anesthesia (reduction of secretions and bronchodilation), gastroenterology (reduction of gut motility and cramps), urology (overactive bladder), and pulmonology (inhaled antimuscarinics for COPD and asthma). Adverse effects commonly include dry mouth, constipation, blurred vision, urinary retention, tachycardia, and cognitive changes, especially in the elderly. They may interact with other anticholinergic drugs and are contraindicated in certain conditions such as angle-closure glaucoma and urinary retention.