Inhibited metabolism w/ ketoconazole & quinidine. Increased conc w/ ketoconazole. Reduced clearance w/ a known CYP2D6 inhibitor. Increased rate of elimination w/ CYP2D6 & CYP3A4 inducers (eg, phenytoin, carbamazepine, dexamethasone, rifampicin & phenobarb). May interfere activity of anticholinergic medications. Synergistic effect w/ succinylcholine, similar neuromuscular blocking agents or cholinergic agonists eg, bethanechol.