Genitourinary Antimuscarinics

Antimuscarinic drugs are, because of their mechanism of action, used in the treatment of a wide variety of conditions. Here, we talk about antimuscarinic drugs in the context of genitourinary medicine.

Antimuscarinics are used in the treatment of the following genitourinary conditions:

  • Reduction of urinary frequency and urgency
  • Reduction of urge incontinence in overactive bladder (OAB)

The antimuscarinic medicines used in the treatment of these conditions include:

  • Oxybutynin
  • Tolterodine, fesoterodine
  • Hyoscyamine
  • Solifenacin, darifenacin

Antimuscarinic drugs are used to treat these conditions because the muscles that control urinary actions are controlled by muscarinic receptors.

Antimuscarinic drugs rebel against the natural tendency of muscarinic receptors – to promote urinary frequency – and help patients by controlling their urge to urinate.

Even though these medicines are indicated to treat urinary frequency and OAB, they only have moderate effect.

Patients can still expect to have some, if residual, symptoms even when taking any of the above medicines.

Mechanism of action

Antimuscarinic drugs bind to muscarinic receptors, inhibiting the effects of acetylcholine.

Muscle movement of the bladder is under the control of the parasympathetic nervous system – meaning that inhibiting muscarinic receptors causes smooth muscle relaxation. It’s this relaxation that increases bladder capacity, reduces urinary frequency, urgency and urge incontinence.

In the treatment of overactive bladder, antimuscarinic effect at M3 receptors is what produces the desired effect. However, newer agents – such as tolterodine – act at both M2 and M3 receptor subtypes.

Side effects

Side effects associated with these medicines include:

  • Dry mouth
  • Constipation
  • Tachycardia
  • Blurred vision

These side effects can be anticipated as they are the typical side effects expected from antimuscarinic drugs (also known as anticholinergic side effects).

Clinical considerations

When we talk about the clinical considerations of antimuscarinic drugs, we need to think about the following factors:

  • That antimuscarinics should be avoided in patients with active urinary tract infections.
  • Anticholinergic side effects – such as dizziness and drowsiness – can prove problematic in certain patient groups, such as the elderly or in patients with dementia.
  • Antimuscarinic drugs should be used with caution alongside other drugs that have antimuscarinic effects – for example: tricyclic antidepressants.
  • Antimuscarinic drugs should be used with caution in patients likely to suffer from angle-closure glaucoma due to the risk of increased intraocular pressure.

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