The most likely contributor
On day 2 she faints briefly while walking. Her heart rate is 46/min and regular, her blood pressure is 124/72 mmHg lying and 118/70 mmHg after 3 minutes standing, and her capillary glucose is 104 mg/dL (5.8 mmol/L). Cholinesterase inhibitors such as donepezil can cause bradycardia and syncope, and beta blockers such as metoprolol add to the effect. The slow heart rate from the two drugs together is the most likely contributor, and the nurse reports it before the next doses.
How the drugs combine
Donepezil increases acetylcholine by inhibiting its breakdown. Although the goal is to boost acetylcholine in the brain, the effect also reaches the heart, where increased vagal (parasympathetic) tone slows the sinus node and atrioventricular conduction. Metoprolol blocks beta-adrenergic stimulation of the heart, removing the sympathetic drive that would normally speed the rate. Together they can slow the heart enough to reduce cardiac output and cause fainting, especially in an older adult.
| Possible cause | Data | Conclusion |
|---|
| Orthostatic hypotension | Fall of 6/2 mmHg on standing | Criterion not met |
| Hypoglycemia | Glucose 104 mg/dL (5.8 mmol/L) | Normal |
| Drug-induced bradycardia | Heart rate 46/min | Most likely |
| Alzheimer progression | Gradual course | Does not explain a sudden faint |
Why the other causes are ruled out
Orthostatic hypotension is defined as a fall of at least 20 mmHg systolic or 10 mmHg diastolic within 3 minutes of standing; her fall of 6/2 mmHg does not meet this criterion, even though she was admitted for dehydration. Hypoglycemia is excluded by a normal capillary glucose. Progression of Alzheimer disease is gradual and does not explain a sudden faint with a heart rate of 46/min.
Nursing actions
The nurse ensures her safety, assesses her for injury from the faint, obtains an electrocardiogram if ordered, reports the bradycardia, and anticipates a review of donepezil and metoprolol before the next doses. Fall precautions are put in place, and she is assisted when walking.
Exam takeaway
Key point Donepezil plus a beta blocker can cause symptomatic bradycardia and syncope. Check the numbers against the definitions to rule out orthostatic hypotension and hypoglycemia.