Donepezil is a commonly used drug in older people that due to its procholinergic effects can provoke bradycardia and neurocardiogenic syncope. Donepezil is metabolized by the cytochrome P450 isozyme 3A4 (CYP3A4). Clarithromycin is a potent inhibitor of CYP3A4, and patients taking both of these drugs may be at increased risk of cardiac adverse events.