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Pronunciation
(trye heks ee FEN i dil)
Generic Available (U.S.)
Yes
Index Terms
Brand Names: Canada
Pharmacologic Category
Pharmacologic Category Synonyms
Use: Labeled Indications
Adjunctive treatment of Parkinson's disease; treatment of drug-induced extrapyramidal symptoms
Pregnancy Risk Factor
C
Pregnancy Considerations
Animal reproduction studies have not been conducted. One case report did not show evidence of adverse events after trihexyphenidyl administration during pregnancy (Robottom, 2011).
Lactation
Excretion in breast milk unknown/use caution
Breast-Feeding Considerations
Anticholinergic agents may suppress lactation.
Contraindications
There are no contraindications listed within the manufacturer's labeling.
Warnings/Precautions
Concerns related to adverse effects:
• Anhidrosis/hyperthermia: May cause anhidrosis and hyperthermia, which may be severe; use with caution in hot weather or during exercise, especially when administered concomitantly with other anticholinergic drugs to chronically-ill patients, alcoholics, patients with CNS disease, or persons doing manual labor in a hot environment.
• CNS effects: May impair physical or mental abilities; patients must be cautioned about performing tasks which require mental alertness (eg, operating machinery or driving).
• Weakness: When given in large doses or to susceptible patients, may cause weakness and inability to move particular muscle groups.
Disease-related concerns:
• Cardiovascular disease: Use with caution in patients with cardiovascular disease, including hypertension.
• GI obstruction: Use with caution in patients with obstructive disease of the GI tract.
• Glaucoma: Use with caution in patients with glaucoma.
• Hepatic impairment: Use with caution in patients with hepatic impairment.
• Mental illness: May exacerbate mental symptoms when used to treat extrapyramidal symptoms.
• Prostatic hyperplasia/urinary stricture: Use with caution in patients with prostatic hyperplasia and/or urinary stricture or retention.
• Renal impairment: Use with caution in patients with renal impairment.
Special populations:
• Elderly: Frequently develop increased sensitivity and require strict dosage regulation; side effects may be more severe in elderly patients with atherosclerotic changes.
Other warnings/precautions:
• Tardive dyskinesia: Does not relieve symptoms of tardive dyskinesia.
Adverse Reactions
Frequency not defined.
Cardiovascular: Tachycardia
Central nervous system: Agitation, confusion, delusions, dizziness, drowsiness, euphoria, hallucinations, headache, nervousness, paranoia, psychiatric disturbances
Dermatologic: Rash
Gastrointestinal: Constipation, dilatation of colon, ileus, nausea, parotitis, vomiting, xerostomia
Genitourinary: Urinary retention
Neuromuscular & skeletal: Weakness
Ocular: Blurred vision, glaucoma, intraocular pressure increased, mydriasis
Metabolism/Transport Effects
None known.
Drug Interactions
AbobotulinumtoxinA: Anticholinergic Agents may enhance the anticholinergic effect of AbobotulinumtoxinA. Risk C: Monitor therapy
Acetylcholinesterase Inhibitors (Central): Anticholinergics may diminish the therapeutic effect of Acetylcholinesterase Inhibitors (Central). Acetylcholinesterase Inhibitors (Central) may diminish the therapeutic effect of Anticholinergics. If the anticholinergic action is a side effect of the agent, the result may be beneficial. Risk C: Monitor therapy
Anticholinergics: May enhance the adverse/toxic effect of other Anticholinergics. Exceptions: Levocabastine (Nasal); Paliperidone. Risk C: Monitor therapy
Cannabinoids: Anticholinergic Agents may enhance the tachycardic effect of Cannabinoids. Risk C: Monitor therapy
OnabotulinumtoxinA: Anticholinergic Agents may enhance the anticholinergic effect of OnabotulinumtoxinA. Risk C: Monitor therapy
Potassium Chloride: Anticholinergic Agents may enhance the ulcerogenic effect of Potassium Chloride. Risk D: Consider therapy modification
Pramlintide: May enhance the anticholinergic effect of Anticholinergics. These effects are specific to the GI tract. Risk D: Consider therapy modification
RimabotulinumtoxinB: Anticholinergic Agents may enhance the anticholinergic effect of RimabotulinumtoxinB. Risk C: Monitor therapy
Secretin: Anticholinergic Agents may diminish the therapeutic effect of Secretin. Risk D: Consider therapy modification
Ethanol/Nutrition/Herb Interactions
Ethanol: Avoid ethanol (may increase CNS depression).
Storage
Store at 20°C to 25°C (68°F to 77°F).
Mechanism of Action
Exerts a direct inhibitory effect on the parasympathetic nervous system. It also has a relaxing effect on smooth musculature; exerted both directly on the muscle itself and indirectly through parasympathetic nervous system (inhibitory effect)
Pharmacodynamics/Kinetics
Metabolism: Hydroxylation of the alicyclic groups
Half-life elimination: 33 hours
Time to peak, serum: 1.3 hours
Excretion: Urine and bile
Dosage
Oral:
Adults:
Parkinson's disease: Initial: 1 mg/day, increase by 2 mg increments at intervals of 3-5 days; usual dose: 6-10 mg/day in 3-4 divided doses; doses of 12-15 mg/day may be required
Drug-induced EPS: Initial: 1 mg/day; increase as necessary to usual range: 5-15 mg/day in 3-4 divided doses
Use in combination with levodopa: Usual range: 3-6 mg/day in divided doses
Elderly: Parkinson's disease: Refer to adult dosing. Note: Conservative initial doses and gradual titration is especially important in patients >60 years of age.
Administration: Oral
May be administered before or after meals; tolerated best if given in 3 daily doses and with food. High doses (>10 mg/day) may be divided into 4 doses, at meal times and at bedtime.
Monitoring Parameters
IOP monitoring and gonioscopic evaluations should be performed periodically
Dietary Considerations
May be taken before or after meals; tolerated best if given with food.
Patient Education
Take with meals if GI upset occurs. Maintain adequate hydration unless instructed to restrict fluid intake; void before taking medication. Do not use alcohol. You may experience drowsiness, confusion, vision changes, increased susceptibility to heat stroke, decreased perspiration, constipation, or dry skin or nasal passages. Report unresolved constipation, chest pain or palpitations, respiratory difficulty, CNS changes (hallucination, loss of memory, nervousness, etc), painful or difficult urination, increased muscle spasticity or rigidity, skin rash, or significant worsening of condition.
Geriatric Considerations
Anticholinergic agents are generally not well tolerated in the elderly (eg, confusion, constipation, urinary retention) and their use should be avoided when possible. In elderly, anticholinergic agents should not be used as prophylaxis against extrapyramidal symptoms.
Additional Information
Incidence and severity of side effects are dose related. Patients may be switched to sustained-action capsules when stabilized on conventional dosage forms.
Dental Health: Effects on Dental Treatment
Key adverse event(s) related to dental treatment: Xerostomia, dry throat (normal salivary flow resumes upon discontinuation). Prolonged xerostomia may contribute to discomfort and dental disease (ie, caries, periodontal disease, and oral candidiasis).
Dental Health: Vasoconstrictor/Local Anesthetic Precautions
No information available to require special precautions
Mental Health: Comment
This agent should not be used for an acute dystonic reaction. No injectable dosage form is available. However, oral dosage forms may be utilized to treat akathisia and pseudoparkinsonism. It is considered to be the least sedating antihistamine used to treat drug-induced EPS.
Nursing: Physical Assessment/Monitoring
Monitor renal function. Monitor for anticholinergic syndrome. Intraocular pressure monitoring and gonioscopic evaluations should be performed periodically.
Dosage Forms
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Elixir, oral, as hydrochloride: 2 mg/5 mL (473 mL)
Tablet, oral, as hydrochloride: 2 mg, 5 mg
Pricing: U.S. (www.drugstore.com)
Elixir (Trihexyphenidyl HCl)
0.4 mg/mL (473): $30.99
Tablets (Trihexyphenidyl HCl)
2 mg (90): $22.99
5 mg (180): $65.99
References
Brocks DR, “Anticholinergic Drugs Used in Parkinson's Disease: An Overlooked Class of Drugs From a Pharmacokinetic Perspective,” J Pharm Pharmaceut Sci, 1999, 2(2):39-46.
Feinberg M, “The Problems of Anticholinergic Adverse Effects in Older Patients,” Drugs Aging, 1993, 3(4):335-48.
He H, McKay G, Wirshing B, et al, “Development and Application of a Specific and Sensitive Radioimmunoassay for Trihexyphenidyl to a Pharmacokinetic Study in Humans,” J Pharm Sci, 1995, 84(5):561-7.
Robottom BJ and Reich SG, "Exposure to High Dosage Trihexyphenidyl During Pregnancy for Treatment of Generalized Dystonia: Case Report and Literature Review," Neurologist, 2011, 17(6):340-1.
International Brand Names
Lexi-Comp.com
Last full review/revision February 2012
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