trihexyphenidyl hydrochloride

trihexyphenidyl hydrochloride

[trīhex′ifen′idil]

an anticholinergic agent.

indications It is prescribed in the treatment of Parkinson's disease and to control drug-induced extrapyramidal reactions.

contraindications Narrow-angle glaucoma, asthma, obstruction of the genitourinary or GI tract, severe ulcerative colitis, or known hypersensitivity to this drug prohibits its use.

adverse effects Among the more serious adverse effects are blurred vision, central nervous system effects, tachycardia, dry mouth, decreased sweating, and hypersensitivity reactions.

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trihexyphenidyl hydrochloride

Apo-Trihex (CA), Broflex (UK), Novo-Hexidyl (CA), PMS-Trihexyphenidyl (CA)

Pharmacologic class: Anticholinergic

Therapeutic class: Antidyskinetic

Pregnancy risk category C

Action

Inhibits parasympathetic nervous system, relaxing smooth muscles and decreasing involuntary movements

Availability

Capsules (sustained-release): 5 mg

Elixir: 2 mg/5 ml

Tablets: 2 mg, 5 mg

⊘Indications and dosages

➣ Adjunct in idiopathic, postencephalitic, or arteriosclerotic parkinsonism

Adults: 1 mg P.O. on first day; may increase in 2-mg increments q 3 to 5 days, up to a maximum of 6 to 10 mg/day. In postencephalitic parkinsonism, 12 to 15 mg P.O. daily. May give sustained-release form (Artane Sequels) in same dosage as conventional form, as a single dose or in two divided doses q 12 hours after daily dosage is determined using conventional tablets or liquid.

➣ Drug-induced extrapyramidal symptoms

Adults: Initially, 1 mg P.O. daily, increased progressively if extrapyramidal symptoms aren't controlled within several hours. Usual dosage range is 5 to 15 mg/day P.O. in divided doses.

Dosage adjustment

• Concurrent use of levodopa or other parasympathetic inhibitor
• Elderly patients

Off-label uses

• Dystonia

Contraindications

• Hypersensitivity to drug, its components, or alcohol (elixir only)
• Angle-closure glaucoma
• Pyloric or duodenal obstruction
• Stenosing peptic ulcer
• Megacolon
• Prostatic hypertrophy or bladder-neck obstruction
• Achalasia
• Myasthenia gravis

Precautions

Use cautiously in:
• chronic renal, hepatic, pulmonary, or cardiac disease; hypertension; tachycardia secondary to cardiac insufficiency; hyperthyroidism
• elderly patients
• pregnant or breastfeeding patients
• children (safety not established).

Administration

• Give with meals. However, if drug causes severe dry mouth, give before meals.
• Administer last dose at bedtime.
• Know that sustained-release capsules shouldn't be used for initial therapy because of their greater strength. Once patient is stabilized on conventional form, he may be switched to sustained-release capsules on basis of milligram-per-milligram of total daily dosage.

Route	Onset	Peak	Duration
P.O.	1 hr	2-3 hr	6-12 hr
P.O. (sustained)	Unknown	Unknown	12-24 hr

Adverse reactions

CNS: dizziness, nervousness, drowsiness, asthenia, headache

CV: orthostatic hypotension, tachycardia

EENT: blurred vision, mydriasis, increased intraocular pressure (IOP), angle-closure glaucoma (with long-term use)

GI: nausea, vomiting, constipation, dry mouth

GU: urinary hesitancy or retention

Interactions

Drug-drug. Amantadine, other anticholinergics (including disopyramide, phenothiazines, quinidine, tricyclic antidepressants): additive anticholinergic effects

Other CNS depressants (such as antihistamines, opioids, sedative-hypnotics): additive CNS depression

Phenothiazines: decreased phenothiazine effects

Drug-herbs. Angel's trumpet, jimsonweed, scopolia: increased anticholinergic effects

Drug-behaviors. Alcohol use: additive CNS depression

Patient monitoring

• With prolonged use, monitor vision and IOP regularly.
• Assess drug efficacy to help guide dosage titration.
• Monitor vital signs. Watch for orthostatic hypotension.
• Closely monitor fluid intake and output. Stay alert for urinary retention.

Patient teaching

• Instruct patient to take with meals or, if severe dry mouth occurs, before meals.
• Tell patient drug has a bitter taste, which may be followed by numbness and tingling in mouth.
• Stress importance of follow-up eye exams.
• Instruct patient to consult prescriber before taking over-the-counter preparations or herbs.
• Advise patient to avoid alcohol and hazardous activities during drug therapy.
• Tell patient to move slowly when sitting up or standing, to avoid dizziness from sudden blood pressure decrease.
• As appropriate, review all other significant adverse reactions and interactions, especially those related to the drugs, herbs, and behaviors mentioned above.