5.22 : Cholinergic Antagonists: Therapeutic Uses

Antimuscarinic drugs have various therapeutic applications by inhibiting parasympathetic stimulation in different systems. Here are the key therapeutic uses of antimuscarinics:

Respiratory Tract: Ipratropium, aclidinium, and tiotropium treat asthma, chronic bronchitis, and chronic obstructive pulmonary disease (COPD). They protect against bronchoconstriction caused by irritants like cigarette smoke, sulfur dioxide, and ozone. They also help reduce nasopharyngeal secretions in common cold-associated rhinorrhea and allergic rhinitis.

Gastrointestinal Tract: Hyoscine and scopolamine relax gastrointestinal smooth muscles, aiding in endoscopy and gastrointestinal radiology procedures. Pirenzepine is preferred for peptic ulcers due to its receptor specificity, while glycopyrrolate and dicyclomine are used to treat irritable bowel syndrome. They reduce functional and nervous diarrhea and control Parkinson's-associated salivation.
Neurological Conditions: Antimuscarinics such as benzhexol, trihexyphenidyl, and benztropine are used to manage Parkinson's disease and antipsychotic-induced extrapyramidal side effects. They suppress cholinergic neurotransmission in the basal ganglia, reducing tremors associated with Parkinson's disease.
Ophthalmic Applications: Homatropine, cyclopentolate, and tropicamide are topically administered for eye examinations and for treating ocular conditions.

Urinary Tract: Antimuscarinics like oxybutynin, tolterodine, trospium, darifenacin, solifenacin, and fesoterodine are used to treat overactive bladder and enuresis in children.

Motion Sickness: Transdermal scopolamine is effective in preventing motion sickness.

Cardiovascular Applications: Atropine treats sinus bradycardia and partial heart block following myocardial infarction.

Antidote for Poisoning: Antimuscarinics serve as antidotes for organophosphorus insecticide poisoning.

It is worth noting that non-selective antimuscarinic agents may cause undesirable side effects, leading to poor long-term patient compliance. Selective agents with receptor or organ specificity exhibit fewer adverse effects, resulting in better patient compliance.