trihexyphenidyl hydrochloride

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.