Overactive bladder drugs: retention, confusion in older adults and blood pressure

Two drug groups with one goal

Overactive bladder causes sudden urges that are hard to control, often with frequency and nocturia. Antimuscarinics such as oxybutynin, tolterodine, fesoterodine and darifenacin block acetylcholine at the bladder and relax the detrusor. Beta-3 adrenergic agonists such as mirabegron and vibegron relax the same muscle through a different receptor, so they avoid most anticholinergic effects.

Medicines are added to, not substituted for, behavioural care. Treatment typically begins with bladder training, pelvic floor exercises and relaxation techniques. Benefit builds slowly: some improvement with oxybutynin may appear within two weeks, but full effect can take six to eight weeks, and mirabegron may need eight weeks or longer. Ask the patient to keep a bladder diary of voids, urgency and leaks, which helps the prescriber judge whether the drug is working.

Antimuscarinic effects and the older adult

Expected anticholinergic effects include dry mouth, constipation, blurred vision and drowsiness. Oxybutynin can also reduce sweating and make it harder for the body to cool down, so teach patients to avoid extreme heat and to seek help for dizziness, confusion or a fast pulse after heat exposure. Narrow-angle glaucoma and incomplete bladder emptying are reasons it may not be used.

Older adults are more vulnerable. MedlinePlus notes that people aged 65 or over should not usually take oxybutynin tablets or syrup, and the MSD Manual advises using strongly anticholinergic drugs judiciously in older patients because they can cause delirium, constipation and faecal impaction. Assess baseline cognition, and review other anticholinergic drugs such as some antihistamines and antipsychotics. New confusion after starting one of these drugs should be reported promptly, not attributed to age.

Watching for urinary retention

A drug prescribed for urgency can cause the opposite problem. Anticholinergics impair bladder contraction and can cause retention with overflow incontinence, which can look like worsening overactive bladder. Mirabegron can cause difficulty emptying, especially combined with solifenacin, and vibegron is stopped if retention develops. Men with prostate enlargement need particular care.

Ask about a weak stream, straining and a feeling of incomplete emptying. Palpate for bladder distension, use a bladder scan for post-void residual as ordered and keep intake and output records. Report a full bladder or rising residual volumes, and teach patients to report difficulty passing urine rather than assuming the medicine is failing.

Beta-3 agonists and blood pressure

Mirabegron may raise blood pressure, so patients need a baseline reading and regular checks during treatment. Caution applies with existing hypertension, bladder outlet obstruction, and kidney or liver disease. Other effects include headache, dizziness, dry mouth, constipation, and back or joint pain. Report a sustained rise in blood pressure to the prescriber.

Teaching covers both groups: swallow extended-release tablets whole without splitting, chewing or crushing, keep taking the medicine because it controls rather than cures symptoms, and limit alcohol with oxybutynin because it worsens drowsiness. Ask about driving until the patient knows how the drug affects their vision and alertness.

Apply it to an exam-style scenario

Consider a hypothetical 81-year-old woman who started oxybutynin tablets a week ago. Her family reports new confusion, she has passed little urine today, and her lower abdomen feels full. Options include encouraging extra fluids, documenting the change as dementia progression, or holding the next dose, scanning her bladder and notifying the prescriber.

Holding the dose, scanning and notifying is best, because new confusion with possible retention after starting an anticholinergic suggests a drug effect. Extra fluids could worsen a distended bladder, and labelling the change as dementia risks missing a reversible cause. The prescriber may switch to another option such as a beta-3 agonist.

Sources and further reading

MedlinePlus: Oxybutynin. Antimuscarinic class, onset over two to eight weeks, glaucoma and incomplete emptying cautions, older adults, drowsiness, alcohol, heat intolerance and whole extended-release tablets.

MedlinePlus: Mirabegron. Beta-3 agonist class, blood pressure monitoring, bladder outlet obstruction caution, retention with solifenacin, side effects and eight-week onset.

MSD Manual Professional: Urinary incontinence in adults. Bladder training first, antimuscarinic agents, judicious use in older patients, anticholinergic retention and delirium, mirabegron blood pressure and vibegron retention.