antimuscarinic drugs

(anticholinergic drugs)

A class of drugs that block the activity of acetylcholine at muscarinic receptors (a subdivision of acetylcholine receptors). They tend to relax smooth muscle (including that of the airways and the gut), reduce the secretion of saliva, digestive juices, and sweat, and dilate the pupil of the eye. They are used as antiparkinsonian drugs, as antispasmodics in the treatment of gastrointestinal pain, as bronchodilators, and to treat incontinence; they are also used to dilate the pupil of the eye in ophthalmic examinations, to antagonize the effects of anticholinesterases, and to increase the heart rate in certain circumstances.

Side effects:
characteristic side effects of antimuscarinic drugs include dry mouth, thirst, blurred vision, dry skin, increased heart rate (following an initial slowing of the heart rate), and difficulty in urinating. Side effects occurring more rarely include confusion (especially in elderly people), drowsiness, dizziness, nausea, and vomiting.

Precautions:
antimuscarinics should not be taken by people with closed-angle (acute) glaucoma, myasthenia gravis, intestinal obstruction due to loss of movement in the intestine, pyloric stenosis, and enlargement of the prostate. They should be used with caution in children and the elderly and in people with reflux oesophagitis, diarrhoea, ulcerative colitis, hypertension (high blood pressure), and conditions causing a fast heart rate.

Interactions with other drugs:
taking two or more antimuscarinic drugs together can increase their side effects. Drugs that can increase antimuscarinic effects include amantadine, antihistamines, disopyramide, nefopam, monoamine oxidase inhibitors, and tricyclic antidepressants.

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