Trihexyphenidyl Hydrochloride

Indications

Trihexyphenidyl Hydrochloride is used for: Extrapyramidal symptoms, Parkinsonism (postencephalitic, arteriosclerotic & idiopathic)

Adult Dose

Oral Drug-induced extrapyramidal symptoms Adult: 5-15 mg/day PO divided q6-8hr Parkinson Disease Adult: Initially, 1 mg daily, gradually increased at intervals of 3-5 days by increments of 2 mg until 6-10 mg daily in 3-4 divided doses. Maintenance: 5-15 mg/day PO divided q6-8hr Parkinsonism Adult: 5-15 mg/day PO divided q6-8hr Elderly: May require lower doses.

Child Dose

Safety and efficacy not established

Renal Dose

Administration

Should be taken with food. Best taken w/ meals. Take before meals if dry mouth occurs, after meals if drooling/nausea occurs. Take at the same time each day.

Contra Indications

Patients with closed-angle glaucoma, chronic pulmonary disease, sick sinus syndrome, thyrotoxicosis, cardiac failure with tachycardia.

Precautions

Patient w/ arteriosclerosis, history of drug idiosyncrasy. CV disease, glaucoma, GI obstruction, prostatic hyperplasia and/or urinary stricture. Not intended for treatment of tardive dyskinesia. Avoid abrupt withdrawal. Hepatic and renal impairment. Elderly. Pregnancy and lactation. Patient Counselling May impair mental or physical abilities e.g. operating machinery or driving. Monitoring Parameters Perform gonioscopic examination prior to initiation of therapy. Monitor intraocular pressure at regular intervals during prolonged treatment.

Pregnancy-Lactation

Pregnancy Category: C Lactation: no data; may inhibit lactation

Interactions

Increased antimuscarinic side effects w/ phenothiazines, clozapine, antihistamines, disopyramide, nefopam and amantadine. Synergistic effect when concomitantly used w/ TCAs. Concurrent admin w/ MAOIs may cause dry mouth, blurred vision, urinary hesitancy or retention and constipation. May antagonise effect of metoclopramide and domperidone on GI function. Reduced absorption of levodopa. May antagonise effect of parasympathomimetics.

Adverse Effects

Side effects of Trihexyphenidyl Hydrochloride : >10% Anticholinergic side effects (30-50%), Rash <1% Suppurative parotitis, Hallucination, Paralytic ileus

Mechanism of Action

Trihexyphenidyl HCl is a tertiary amine antimuscarinic which exerts a direct inhibitory effect on the parasympathetic nervous system. It also exhibits a direct spasmolytic action on smooth muscle, weak mydriatic, antisialagogue and cardiovagal blocking effects.