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Class: Anticholinergic Agents
VA Class: AU350
CAS Number: 52-49-3

Medically reviewed by on Sep 21, 2021. Written by ASHP.


Antimuscarinic antiparkinsonian agent.

Uses for Trihexyphenidyl

Parkinsonian Syndrome

Adjunctive treatment of all forms of parkinsonian syndrome.

May reduce the frequency and duration of oculogyric crises, salivation, spastic contractions, and dyskinesia, and relieve mental inertia and depression characteristic of all forms of parkinsonian syndrome.

Drug-Induced Extrapyramidal Reactions

Control of extrapyramidal reactions induced by antipsychotic agents (e.g., phenothiazines, thioxanthenes).

Trihexyphenidyl Dosage and Administration


Oral Administration

Administer orally before or after meals, depending on patient reaction. Administer before meals in patients with excessive xerostomia. Administer after meals if nausea occurs.

May be administered 3 times daily; if a fourth dose is required, administer at bedtime.

Mint candies, chewing gum, water, or administration of a saliva substitute (e.g., Xero-lube) may relieve xerostomia that may accompany administration after meals.


Available as trihexyphenidyl hydrochloride; dosage expressed in terms of the salt.

Adjust dosage carefully according to individual requirements and response.


Parkinsonian Syndrome

Initially, 1 mg on first day. Dosages may be increased in 2-mg increments at 3- to 5-day intervals up to a maximum of 6–10 mg daily.

Postencephalitic patients: 12–15 mg daily may be required.

When trihexylphenidyl is used as an adjunct to levodopa, consider reducing levodopa and trihexyphenidyl dosages. Generally, 3–6 mg daily of trihexyphenidyl hydrochloride is adequate.

If trihexyphenidyl is replacing another antiparkisonian agent, increase trihexyphenidyl dose as needed while decreasing other drug dose until complete replacement is achieved.

Drug-Induced Extrapyramidal Reactions

Usual dosage: 5–15 mg total daily dosage.

Initially, 1 mg; if extrapyramidal reactions are not controlled within a few hours, progressively increase dosage until control is achieved.

Alternatively, to achieve a more rapid control, reduce dosage of the drug causing the reaction, then adjust the dosage of both drugs to attain the desired drug effect without extrapyramidal symptoms. Once control of extrapyramidal reactions has been maintained for several days, dosage of trihexyphenidyl may be reduced or discontinued.

Prescribing Limits


Parkinsonian Syndrome

Maximum of 6–10 mg daily in most patients; postencephalitic patients may require 12–15 mg daily.

Special Populations

Hepatic Impairment

No specific dosage recommendations at this time.

Renal Impairment

No specific dosage recommendations at this time.

Geriatric Patients

Patients ≥60 years of age: Initiate with low dosage; titrate dosage gradually.

Cautions for Trihexyphenidyl


  • Known hypersensitivity to trihexylphenidyl or any ingredient in the formulation.



Ophthalmic Effects

Possible increased ocular tension. Possible precipitation of glaucoma in patients receiving prolonged therapy.

Use with caution in patients with glaucoma.

Periodic gonioscopic evaluation and intraocular pressure monitoring recommended.

General Precautions

Tardive Dyskinesia

Antiparkinsonian agents do not alleviate symptoms of tardive dyskinesia and may aggravate these symptoms.

Cardiovascular Effects

Possible tachycardia; use with caution and carefully monitor patients with cardiac disease or hypertension.

GU Effects

Possible urinary hesitancy and retention; use with caution and carefully monitor patients with prostatic hypertrophy or obstructive disease of the GU tract.

CNS Effects

Possible mental confusion, disorientation, agitation, hallucinations, and psychotic-like symptoms.

GI Effects

Possible decreased intestinal mobility and paralytic ileus; use with caution in patients with obstructive diseases of the GI tract.

Specific Populations


Category C.

Geriatric Use

Possibility exists of greater sensitivity to the drug in some geriatric individuals.

Hepatic Impairment

Use with caution; careful monitoring recommended.

Renal Impairment

Use with caution; careful monitoring recommended.

Common Adverse Effects

Dry mouth, blurred vision, dizziness, nausea, nervousness.

Interactions for Trihexyphenidyl

Specific Drugs



Anticholinergic agents

Increased risk of adverse anticholinergic effects

Trihexyphenidyl Pharmacokinetics


Rapidly absorbed from the GI tract following oral administration.


Following oral adminstration, onset of action occurs within 1 hour.


6–12 hours.


Elimination Route

Excreted principally in urine, probably as unchanged drug.





20–25°C. Do not freeze.




  • Exhibits atropine-like action and exerts antispasmodic effects on parasympathetic-innervated peripheral structures, including smooth muscle.

  • Exact mechanism of action in parkinsonian syndrome not understood; may result from blockade of efferent impulses and from central inhibition of cerebral motor centers.

  • Competitively inhibits acetylcholine or other cholinergic stimuli at autonomic effectors innervated by postganglionic nerves.

  • Exhibits weak mydriatic, antisialagogue, and cardiovagal blocking effects.

Advice to Patients

  • Potential for drug to impair mental alertness or physical coordination; use caution when driving or operating machinery until effects on individual are known.

  • Importance of informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs and dietary or herbal supplements, as well as concomitant illnesses.

  • Importance of women informing clinicians if they are or plan to become pregnant or plan to breast-feed.

  • Importance of informing patients of other important precautionary information. (See Cautions.)


Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

Trihexyphenidyl Hydrochloride


Dosage Forms


Brand Names




2 mg/5 mL*

Trihexyphenidyl Hydrochloride Elixir

Mikart, Pharmaceutical Associates, Pharmaceutical Ventures


2 mg*

Trihexyphenidyl Hydrochloride Tablets

URL, Vintage, Watson, West-Ward

5 mg*

Trihexyphenidyl Hydrochloride Tablets

URL, Vintage, Watson, West-Ward

AHFS DI Essentials™. © Copyright 2022, Selected Revisions October 1, 2007. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.

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