TRIHEXYPHENIDYL HYDROCHLORIDE

TRIHEXYPHENIDYL HYDROCHLORIDE
(trye-hex-ee-fen'i-dill)
Aparkane

, Apo-Trihex

, Novohexidyl

Classifications: anticholinergic; antiparkinson agent; anti-muscarinic; antispasmodic;
Therapeutic: antiparkinson; antispasmodic
Prototype: Atropine
Pregnancy Category: C

Availability

2 mg, 5 mg tablets; 2 mg/5 mL elixir

Action

Synthetic tertiary amine anticholinergic agent similar to atropine. Thought to act by blocking excess of acetylcholine at certain cerebral synaptic sites. Relaxes smooth muscle by direct effect and by atropinelike blocking action on the parasympathetic nervous system.

Therapeutic Effect

Anticholinergic agent diminishes the characteristic tremor of Parkinson's disease. Antispasmodic action appears to be one-half that of atropine.

Uses

Symptomatic treatment of all forms of parkinsonism (arteriosclerotic, idiopathic, postencephalitic). Also to prevent or control drug-induced extrapyramidal disorders.

Unlabeled Uses

Huntington's chorea, spasmodic torticollis.

Contraindications

Narrow-angle glaucoma; tardive dyskinesia; pregnancy (category C), lactation. Safe use in children is not established.

Cautious Use

History of drug hypersensitivities; arteriosclerosis; hypertension; cardiac disease, kidney or liver disorders; myasthenia gravis; alcoholism; obstructive diseases of GI or genitourinary tracts; older adults with prostatic hypertrophy.

Route & Dosage

Parkinsonism
Adult: PO 1 mg day 1, 2 mg day 2, then increase by 2 mg q3–5d up to 6–10 mg/d in 3 or more divided doses (max: 15 mg/d)

Extrapyramidal Effects
Adult: PO 5–15 mg/d in divided doses

Administration

Oral

Give before or after meals, depending on how patient reacts. Older adults and patients prone to excessive salivation (e.g., postencephalitic parkinsonism) may prefer to take drug after meals. If drug causes excessive mouth dryness, it may be better given before meals, unless it causes nausea.
Once stabilized on conventional dosage forms, patient may be switched to sustained release capsules to permit once- or twice-a-day dosing.
Do not crush or chew sustained release capsules. These must be swallowed whole.
Store at 15°–30° C (59°–86° F) in tight container unless otherwise directed.

Adverse Effects (≥1%)

GI: Dry mouth, nausea, constipation. Special Senses: Blurred vision, mydriasis, photophobia, angle-closure glaucoma. Urogenital: Urinary hesitancy or retention. CNS: Dizziness, nervousness, insomnia, drowsiness, confusion, agitation, delirium, psychotic manifestations, euphoria. CV: Tachycardia, palpitations, hypotension, orthostatic hypotension. Body as a Whole: Hypersensitivity reactions.

Interactions

Drug: Reduces therapeutic effects of chlorpromazine, haloperidol, phenothiazines; increases bioavailability of digoxin; mao inhibitors potentiate actions of trihexyphenidyl. Herbal: Betel nut may increase risk of extrapyramidal symptoms.

Pharmacokinetics

Absorption: Readily from GI tract. Onset: Within 1 h. Peak: 2–3 h. Duration: 6–12 h. Elimination: In urine.

Nursing Implications

Assessment & Drug Effects

Be aware that incidence and severity of adverse effects are usually dose related and may be minimized by dosage reduction. Older adults appear more sensitive to usual adult doses.
Monitor vital signs. Pulse is a particularly sensitive indicator of response to drug. Report tachycardia, palpitations, paradoxical bradycardia, or fall in BP.
Assess for and report severe CNS stimulation (see ADVERSE EFFECTS) that occurs with high doses, and in patients with arteriosclerosis, or those with history of hypersensitivity to other drugs.
In patients with severe rigidity, tremors may appear to be accentuated during therapy as rigidity diminishes.
Monitor daily I&O if patient develops urinary hesitancy or retention. Voiding before taking drug may relieve problem.
Check for abdominal distention and bowel sounds if constipation is a problem.
Monitor intraocular pressure at regular intervals.
Provide close follow-up care. Tolerance may develop, necessitating dosage adjustment or use of combination therapy. Patients ≥60 y frequently develop sensitivity to drug action.

Patient & Family Education

Learn measures to relieve drug-induced dry mouth; rinse mouth frequently with water and suck ice chips, sugarless gum, or hard candy. Maintain adequate total daily fluid intake.
Avoid excessive heat because drug suppresses perspiration and, therefore, heat loss.
Do not to engage in potentially hazardous activities requiring alertness and skill. Drug causes dizziness, drowsiness, and blurred vision. Help walking may be indicated.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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