Trihexyphenidyl Hydrochloride(trye hex ee fen’ i dill)
Apo-Trihex (CAN)
PREGNANCY CATEGORY C
Drug class
Antiparkinsonian (anticholinergic type)
Therapeutic Actions
Has anticholinergic activity in the CNS that is believed to help normalize the hypothesized imbalance of cholinergic and dopaminergic neurotransmission created by the loss of dopaminergic neurons in the basal ganglia of the brain of parkinsonism patients; reduces severity of rigidity and reduces to a lesser extent the akinesia and tremor that characterize parkinsonism; less effective overall than levodopa; peripheral anticholinergic effects suppress secondary symptoms of parkinsonism, such as drooling.
Indications
Adjunct in the treatment of parkinsonism (postencephalitic, arteriosclerotic, and idiopathic)
Adjuvant therapy with levodopa for the treatment of Parkinson disease
Control of drug-induced extrapyramidal disorders
Contraindications and Cautions
Contraindicated with hypersensitivity to trihexyphenidyl; glaucoma, especially angle-closure glaucoma; pyloric or duodenal obstruction, stenosing peptic ulcers, achalasia (megaesophagus); myasthenia gravis; lactation.
Use cautiously with cardiac arrhythmias, hypertension, hypotension, hepatic or renal impairment, alcoholism, chronic illness, people who work in hot environment, pregnancy, prostatic hypertrophy or bladder neck obstructions.
Available Forms
Tablets—2, 5 mg; elixir—2 mg/5 mL
Dosages
Adults
Tablets
Parkinsonism: 1 mg PO the first day. Increase by 2-mg increments at 3- to 5-day intervals until a total of 6–10 mg is given daily. Postencephalitic patients may require 12–15 mg/day PO. Tolerated best if daily dose is divided into three (or four) doses administered at mealtimes (and bedtime).
Concomitant use with levodopa: Usual dose of each may need to be reduced; however, trihexyphenidyl has been shown to decrease bioavailability of levodopa. Adjust dosage on basis of response. 3–6 mg/day PO of trihexyphenidyl is usually adequate.
Concomitant use with other anticholinergics: Gradually substitute trihexyphenidyl for all or part of the other anticholinergic and reduce dosage of the other anticholinergic gradually.
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