An 82-year-old woman with a history of mild Alzheimer’s dementia is started on donepezil 10 mg nightly to help with memory and cognitive function. After several weeks, her family reports that she’s been waking up multiple times per night to urinate and has complained of increased urinary urgency during the day. Her primary care provider attributes this to overactive bladder and prescribes oxybutynin 5 mg twice daily.
A few weeks later, the patient presents for a follow-up appointment, where her heart rate is found to be 48 beats per minute. She reports occasional lightheadedness and fatigue. An ECG confirms sinus bradycardia.
Med Review and Discussion
Donepezil, a cholinesterase inhibitor, increases acetylcholine levels in the brain to enhance cognitive function. However, increased cholinergic activity can also affect peripheral muscarinic receptors, leading to side effects such as urinary frequency, nausea, and bradycardia.
In this case, the donepezil likely caused both the urinary symptoms and the slowed heart rate. Oxybutynin, an anticholinergic agent, was then prescribed to counteract the urinary frequency — but it also works against donepezil’s mechanism of action by blocking acetylcholine, potentially reducing the cognitive benefit the medication was intended to provide.
Clinical Takeaway
This is a classic prescribing cascade — where a new drug (oxybutynin) is added to treat an adverse effect (urinary frequency) caused by another drug (donepezil). The addition not only introduces new risks (confusion, dry mouth, constipation) but also counteracts the therapeutic purpose of the original medication. Additionally, the bradycardia highlights another important cholinergic effect that can be clinically significant, particularly in older adults.
It is absolutely critical to assess the potential for adverse effects when new symptoms arise. In this case, oxybutynin may not have been started if it was recognized that donepezil was causing the clinical problems in the first place. For more information on donepezil and oxybutynin, please check out these podcast episodes.
- 30 medication mistakes PDF
- 18+ Page Drug Interaction PDF
- 10 Commandments of Polypharmacy Webinar based on my experiences in clinical practice
Popular Amazon Books
0 Comments