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

Medically reviewed by Drugs.com. Last updated on Sep 21, 2020.

• Overview
• Side Effects
• Dosage
• Professional
• Interactions
• More

Introduction

Antimuscarinic antiparkinsonian agent.^{a b}

Uses for Trihexyphenidyl

Parkinsonian Syndrome

Adjunctive treatment of all forms of parkinsonian syndrome.^{a b}

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.^b

Drug-Induced Extrapyramidal Reactions

Control of extrapyramidal reactions induced by antipsychotic agents (e.g., phenothiazines, thioxanthenes).^{a b}

Trihexyphenidyl Dosage and Administration

Administration

Oral Administration

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

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

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

Dosage

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

Adjust dosage carefully according to individual requirements and response.^b

Adults

Parkinsonian Syndrome

Oral

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

Postencephalitic patients: 12–15 mg daily may be required.^{a b}

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

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

Drug-Induced Extrapyramidal Reactions

Oral

Usual dosage: 5–15 mg total daily dosage.^{a b}

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

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.^b Once control of extrapyramidal reactions has been maintained for several days, dosage of trihexyphenidyl may be reduced or discontinued.^b

Prescribing Limits

Adults

Parkinsonian Syndrome

Oral

Maximum of 6–10 mg daily in most patients; postencephalitic patients may require 12–15 mg daily.^{a b}

Special Populations

Hepatic Impairment

No specific dosage recommendations at this time.^a

Renal Impairment

No specific dosage recommendations at this time.^a

Geriatric Patients

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

Cautions for Trihexyphenidyl

Contraindications

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

Warnings/Precautions

Warnings

Ophthalmic Effects

Possible increased ocular tension.^a Possible precipitation of glaucoma in patients receiving prolonged therapy.^{a c}

Use with caution in patients with glaucoma.^{a c}

Periodic gonioscopic evaluation and intraocular pressure monitoring recommended.^{a b}

General Precautions

Tardive Dyskinesia

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

Cardiovascular Effects

Possible tachycardia;^a use with caution and carefully monitor patients with cardiac disease or hypertension.^{a c}

GU Effects

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

CNS Effects

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

GI Effects

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

Specific Populations

Pregnancy

Category C.^d

Geriatric Use

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

Hepatic Impairment

Use with caution; careful monitoring recommended.^a

Renal Impairment

Use with caution; careful monitoring recommended.^a

Common Adverse Effects

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

Interactions for Trihexyphenidyl

Specific Drugs

Trihexyphenidyl Pharmacokinetics

Absorption

Rapidly absorbed from the GI tract following oral administration.^b

Onset

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

Duration

6–12 hours.^b

Elimination

Elimination Route

Excreted principally in urine, probably as unchanged drug.^b

Stability

Storage

Oral

Elixir

20–25°C.^e Do not freeze.^e

Tablets

20–25°C.^a

Actions

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

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

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

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

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.^a

• 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.^a

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

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

Preparations

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

Medical Disclaimer