Trihexyphenidyl (TPN)

Trihexyphenidyl is an antiparkinsonian agent of the antimuscarinic class. It has been in clinical usage for decades. The drug is available as the hydrochloride salt. The exact mechanism of action in parkinsonian syndromes is not precisely understood, but it is known that trihexyphenidyl blocks efferent impulses in parasympathetically innervated structures like smooth muscles (spasmolytic activity), salivary glands, and eyes (mydriasis). In higher doses direct central inhibition of cerebral motor centers may contribute. In very high doses central toxicity as seen in atropine overdose is noted. Trihexyphenidyl is rapidly absorbed from the gastrointestinal tract. Trihexyphenidyl is used for the symptomatic treatment of Parkinson's disease in mono- and combination therapy. It is active in postencephalitic, arteriosclerotic, and idiopathic forms.