It also exhibits a direct spasmolytic action and weak mydriatic, anti-sialogogue and cardiovagal blocking effects. In small doses, trihexyphenidyl depresses the CNS but larger doses cause cerebral excitement resembling the signs of atropine toxicity. Trihexyphenidyl is rapidly absorbed from the gastrointestinal tract. After oral administration, the onset of action occurs within 1 hour, peak effects last 2 to 3 hours and the duration of action is 6 to 12 hours. It is excreted in the urine, probably as unchanged drug.
Precautions Closely observe patients with cardiac, liver, kidney or hypertensive disorders.
Patients undergoing prolonged therapy should be subjected to careful periodic review to avoid untoward reactions. Trihexyphenidyl should be used with caution in patients with glaucoma, obstructive disease of the gastrointestinal or genitourinary tracts, and in elderly males with possible prostatic hypertrophy. Trihexyphenidyl may cause anhidrosis. Caution should be exercised during hot weather especially if given with other anticholinergic drugs. Incipient glaucoma may be precipitated by trihexyphenidyl.