TeacherOfMedicine: Antimuscarinics, genitourinary uses

To reduce urinary frequency, urgency and urge incontinence in overactive bladder, as a first-line pharmacological treatment if bladder training is ineffective.

Antimuscarinic drugs bind to muscarinic receptors, where they act as a competitive inhibitor of acetylcholine. Contraction of the smooth muscle of the bladder is under parasympathetic control. Blocking muscarinic receptors therefore promotes bladder relaxation, increasing bladder capacity. In patients with overactive bladder, this may reduce urinary frequency, urgency and urge incontinence. Antimuscarinics useful in treating overactive bladder tend to be relatively selective for the M3 receptor, which is the main muscarinic receptor subtype in the bladder.

Predictably from their antimuscarinic action, dry mouth is a very common side effect of these drugs. Other classic antimuscarinic side effects such as tachycardia, constipation and blurred vision are also common. Urinary retention may occur if there is bladder outflow obstruction.

Antimuscarinics are contraindicated in the context of urinary tract infection. Urinalysis is therefore an important part of assessment before prescribing treatment for overactive bladder. Central nervous system side effects (drowsiness and confusion) can be particularly problematic in the elderly and especially patients with dementia. Antimuscarinics should be used with caution in patients susceptible to angle-closure glaucoma, in whom they can precipitate a dangerous rise in intraocular pressure. They should be used with caution in patients at risk of arrhythmias (e.g. those with significant cardiac disease) and, for obvious reasons, those at risk of urinary retention.

Adverse effects are more pronounced when combined with other drugs that have antimuscarinic effects, such as tricyclic antidepressants.

TeacherOfMedicine