Generic Medicine Info
Indications and Dosage
Drug-induced extrapyramidal symptoms
Adult: Initially, 1 mg daily, increased to 5-15 mg daily in 3-4 divided doses.
Elderly: May require lower doses.

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. Postencephalitic patients: Up to 12-15 mg daily.
Elderly: May require lower doses.
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.
Special 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.
Adverse Reactions
Dryness of the mouth, nausea, constipation, vomiting, dizziness, drowsiness, headache, blurred vision, mydriasis, nervousness, tachycardia, urinary hesitancy or retention, increased intraocular tension, angle-closure glaucoma, weakness, rashes, dilatation of the colon, paralytic ileus, and suppurative parotitis. Rarely, psychiatric disturbances (e.g. delusion, amnesia, depersonalization, sense of unreality, paranoia).
Patient Counseling Information
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.
Symptoms: Flushing, dryness of the skin, dilated pupils, dry mouth and tongue, tachycardia, rapid respiration, hyperpyrexia, HTN, nausea, vomiting, rashes on face or upper trunk; restlessness, confusion, hallucinations, paranoid and psychotic reactions, incoordination, delirium and occasionally convulsions; CNS depression may occur w/ coma, circulatory and resp failure, death. Management: Symptomatic and supportive treatment. Maintain adequate airway. Admin diazepam to control excitement and convulsions but consider risk of CNS depression. Hypoxia and acidosis should be corrected.
Drug 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.
Food Interaction
Sedative effects may be potentiated w/ alcohol.
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.
Onset: W/in 1 hr.
Duration: 6-12 hr.
Absorption: Rapidly and well absorbed from the GI tract. Time to peak plasma concentration: 1.3 hr.
Metabolism: Undergoes hydroxylation of the alicyclic group.
Excretion: Via urine (as unchanged drug) and bile. Elimination half-life: 33 hr.
Chemical Structure

Chemical Structure Image

Source: National Center for Biotechnology Information. PubChem Database. Trihexyphenidyl, CID=5572, (accessed on Jan. 23, 2020)

Store between 20-25°C.
MIMS Class
Antiparkinsonian Drugs
Anon. Trihexyphenidyl. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. Accessed 04/09/2014.

Buckingham R (ed). Trihexyphenidyl Hydrochloride. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. Accessed 04/09/2014.

McEvoy GK, Snow EK, Miller J et al (eds). Trihexyphenidyl Hydrochloride. AHFS Drug Information (AHFS DI) [online]. American Society of Health-System Pharmacists (ASHP). Accessed 04/09/2014.

Disclaimer: This information is independently developed by MIMS based on Trihexyphenidyl from various references and is provided for your reference only. Therapeutic uses, prescribing information and product availability may vary between countries. Please refer to MIMS Product Monographs for specific and locally approved prescribing information. Although great effort has been made to ensure content accuracy, MIMS shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2024 MIMS. All rights reserved. Powered by
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