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Trihexyphenidyl Hydrochloride

Pronunciation

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

Introduction

Antimuscarinic antiparkinsonian agent.a b

Uses for Trihexyphenidyl Hydrochloride

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

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Drug-Induced Extrapyramidal Reactions

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

Trihexyphenidyl Hydrochloride 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 Hydrochloride

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 Hydrochloride

Specific Drugs

Drug

Interaction

Anticholinergic agents

Increased risk of adverse anticholinergic effectsc

Trihexyphenidyl Hydrochloride 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.

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

Trihexyphenidyl Hydrochloride

Routes

Dosage Forms

Strengths

Brand Names

Manufacturer

Oral

Elixir

2 mg/5 mL*

Trihexyphenidyl Hydrochloride Elixir

Mikart, Pharmaceutical Associates, Pharmaceutical Ventures

Tablets

2 mg*

Trihexyphenidyl Hydrochloride Tablets

URL, Vintage, Watson, West-Ward

5 mg*

Trihexyphenidyl Hydrochloride Tablets

URL, Vintage, Watson, West-Ward

Comparative Pricing

This pricing information is subject to change at the sole discretion of DS Pharmacy. This pricing information was updated 02/2014. Actual costs to patients will vary depending on the use of specific retail or mail-order locations and health insurance copays.

Trihexyphenidyl HCl 0.4MG/ML Elixir (PHARMACEUTICAL ASSOCIATES): 473/$30.99 or 1419/$79.97

Trihexyphenidyl HCl 2MG Tablets (WATSON LABS): 90/$22.99 or 180/$39.97

Trihexyphenidyl HCl 5MG Tablets (WEST-WARD): 180/$65.99 or 280/$95.97

AHFS DI Essentials. © Copyright, 2004-2014, Selected Revisions October 1, 2007. American Society of Health-System Pharmacists, Inc., 7272 Wisconsin Avenue, Bethesda, Maryland 20814.

References

a. Watson Laboratories Inc. trihexyphenidyl hydrochloride tablets, USP. prescribing information. Corona, CA; 2005 May.

b. AHFS drug information 2006. McEvoy GK, ed. Trihexyphenidyl. Bethesda, MD: American Society of Health-System Pharmacists; 2006:1256.

c. AHFS drug information 2006. McEvoy GK, ed. Antimuscarinics/Antispasmodics General Statement. Bethesda, MD: American Society of Health-System Pharmacists; 2006:1257-64].

d. Briggs GG, Freeman RK, Yaffe SJ. Drugs in pregnancy and lactation, 7th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2005:1628

e. Pharmaceutical Associates, Inc. Trihexyphenidyl HCl elixir prescribing information. Greenville, SC; 2002 May.

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