Bradycardia due to trihexyphenidyl hydrochloride

A chronic schizophrenic patient was treated with an anticholinergic drug, trihexyphenidyl hydrochloride. The patient developed, paradoxically, sinus bradycardia. The reaction was specific to trihexyphenidyl and not to other anticholinergic drugs. This antidyskinetic drug is widely used in clinical psychiatric practice and physicians should be aware of this side effect.