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|Trihexyphenidyl Hydrochloride

Trihexyphenidyl Hydrochloride

Trade Names:
Artane
- Tablets 2 mg
- Tablets 5 mg
- Elixir 2 mg/5 mL

Trade Names:
Artane Sequels
- Capsules, sustained-release 5 mg

Trade Names:
Trihexy-2
- Tablets 2 mg

Trade Names:
Trihexy-5
- Tablets 5 mg

Mechanism of Action

Pharmacology

Exerts direct inhibitory effect on parasympathetic nervous system by inhibiting actions of acetylcholine; has relaxing effect on smooth musculature.

Pharmacokinetics

Absorption

T _max is 1 to 1.3 hr, C _max is 87.2 mcg/L, and oral bioavailability is approximately 100%. Trihexyphenidyl is tolerated best in divided doses and taken at mealtimes.

Elimination

Trihexyphenidyl t _½ is 5.6 to 10.2 hr.

Indications and Usage

Adjunct in treatment of all forms of parkinsonism (postencephalitic, arteriosclerotic, and idiopathic); adjuvant therapy with levodopa for control of drug-induced extrapyramidal disorders.

Maintenance therapy after patients have been stabilized on tablets or elixir.

Contraindications

Standard considerations.

Dosage and Administration

PO 1 or 2 mg first day; increase by 3 mg increments at intervals of 3 to 5 days, until 6 to 10 mg given daily in divided doses. Some postencephalitic patients may require total daily dose of 12 to 15 mg. Usually given tid at mealtimes. High doses may be taken qid, at mealtimes and at bedtime.

Gradually initiate trihexyphenidyl with progressive reduction of other anticholinergic.

Amount and frequency is individualized. Start with single 1 mg dose. If symptoms are not controlled in few hr, progressively increase until controlled. Daily dosage usually ranges 5 to 15 mg in divided doses.

Not for initial therapy. Once patient is stabilized, may switch on equipotent daily basis. Give as single dose after breakfast or in bid doses 12 hr apart.

Storage/Stability

Store at room temperature in light-resistant container. Avoid freezing the elixir.

Drug Interactions

Schizophrenic symptoms may worsen; haloperidol levels may decrease and tardive dyskinesia may develop.

Actions of phenothiazines may be decreased.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Cardiovascular

Tachycardia; palpitations; hypotension.

CNS

Dizziness; nervousness; psychiatric manifestations such as delusions or hallucinations; mental confusion; agitation; disturbed behavior.

Dermatologic

Rash.

EENT

Blurred vision; angle-closure glaucoma; difficulty swallowing.

GI

Dry mouth; nausea; vomiting; constipation; suppurative parotitis; dilation of colon; paralytic ileus.

Genitourinary

Urinary retention; urinary hesitancy; impotence.

Miscellaneous

Fever; flushing; decreased sweating; heat illness.

Precautions

Pregnancy

Category C .

Lactation

Undetermined.

Children

Safety and efficacy not established.

Elderly

More susceptible to adverse effects.

Special Risk Patients

Use drug with caution in patients with tachycardia, arrhythmias, hypertension, hypotension, prostatic hypertrophy, liver or kidney disorders, obstructive disease of GI tract.

Anticholinergic effect

Concomitant use of other drugs with anticholinergic effects will have additive effects.

Heat illness

Give with caution during hot weather. Severe anhidrosis and fatal hyperthermia may occur.

Ophthalmic

Incipient narrow-angle glaucoma may be precipitated by drug use; therefore, closely monitor patient for symptoms and evaluate IOP at regular, periodic intervals.

Overdosage

Symptoms

CNS depression, dry skin, dry mucous membranes, fever, dilated or sluggish pupils, respiratory depression, circulatory collapse, coma.