Muscarinic receptor antagonists
Muscarinic receptor antagonists (MRAs) are a group of drugs most commonly used to treat urgency urinary incontinence (UUI). They help control UUI by relaxing the muscle in the bladder wall. They block the involuntary nerve signals that cause the bladder wall to contract and the bladder to empty. As a result, sudden uncontrollable bladder contractions happen less often. Because of the muscle relaxation, the capacity of the bladder to hold urine also increases. This reduces the need to urinate.
MRAs can be used to manage the frequent need to urinate at night, a condition known as nocturia.
MRAs are not effective for stress urinary incontinence (SUI) because this is generally not caused by an overactive detrusor muscle. There are several types of MRAs:
- Trospium chloride
Most MRAs are taken as a pill. Some are taken once a day and work for 24 hours. Others can be taken multiple times a day and have an immediate but shorter effect. Oxybutynin is also available as a cream or skin patch.
The immediate-release versions of MRAs are helpful if you experience incontinence only at certain times, for instance at night. They also help to manage incontinence if you want to take medication only in specific situations, like when travelling. Immediate-release MRAs generally cause more side-effects compared to the slow-release MRAs.
Side-effects of MRAs are usually mild. They may include dry mouth and eyes, constipation, difficulties urinating, blurred vision, and dizziness. In the elderly, MRAs can cause impaired memory and confusion. Especially oxybutynin can have these effects.