May enhance sedative effects of CNS depressants including alcohol, barbiturates, hypnotics, opioid analgesics, anxiolytic sedatives & antipsychotics. Additive antimuscarinic action w/ other antimuscarinic drugs eg, atropine & some antidepressants. Hazardous ventricular arrhythmias w/ nonsedating antihistamines astemizole & terfenadine. May mask warning signs of damage caused by ototoxic drugs eg, aminoglycosides.