donepezil + dexamethasone

monitor bleeding signs/symptoms; in pts with myasthenia gravis, D/C cholinesterase inhibitors at least 24h before starting corticosteroids: combo may decr. donepezil levels, efficacy; may incr. risk of GI ulceration, perforation, bleeding; may cause extreme weakness in myasthenia gravis (hepatic metabolism induced; additive effects; mechanism unknown)

donepezil + benztropine

caution advised: combo may decr. efficacy of both drugs (antagonistic effects)