Trihexyphenidyl
Trihexyphenidyl is a generic medication for the drug :
Trihexyphenidyl medication comes in several different strengths; click on the strength you need to view prices from pharmacies competing to earn your business.
|
Trihexyphenidyl 2 mg
|
Trihexyphenidyl 5 mg
|
Pharmacology
Pharmacokinetics
Following oral administration, trihexyphenidyl is rapidly absorbed from the gastrointestinal tract. Onset of action is within 1 hour of administration. Peak effects of the drug last for 2 to 3 hours and the duration of action is 6 to 12 hours. Trihexyphenidyl is excreted in the urine, probably as unchanged drug.
Indications
Adjunctive therapy in the symptomatic treatment of Parkinsonism and drug-induced parkinsonian symptoms.
Precautions
Geriatrics
Geriatric patients are frequently more sensitive to the adverse effects of anticholinergic medications, including trihexyphenidyl. These patients may require lower doses, especially at the onset of therapy, and slower dose titration than younger adults.
Drug Interactions
Amantadine: Trihexyphenidyl and other anticholinergic drugs may potentiate the CNS side effects of amantadine. Monitor patients for this effect and reduce the dose of one or both drugs as necessary.
Anticholinergics: Trihexyphenidyl may enhance the anticholinergic effects of drugs including atropine, MAO inhibitors, tricyclic antidepressants and phenothiazines. Paralytic ileus (sometimes fatal), hyperthermia and heat stroke may occur. Advise patients to report gastrointestinal problems, fever or heat intolerance promptly.
CNS depressants: Trihexyphenidyl in small doses, may enhance the CNS depressant effects of drugs including alcohol, anticonvulsants, barbiturates, MAO inhibitors, opioid analgesics, phenothiazines and tricyclic antidepressants.
Cholinesterase Inhibitors: Theoretically, trihexyphenidyl and other anticholinergic drugs that readily penetrate the blood-brain barrier may interfere with the action of centrally acting cholinesterase inhibitors (e.g., donepezil, galantamine, rivastigmine).In addition, cholinesterase inhibitors have the potential to interfere with the activity of anticholinergic medications.
Levodopa: When trihexyphenidyl is used in combination with levodopa, the dosage of each drug may have to be reduced.
Occupational Hazards
Trihexyphenidyl may impair mental and/or physical abilities required for performance of hazardous tasks such as operating machinery or driving a motor vehicle.
Lactation
See Pregnancy.
Children
See Pregnancy.
Pregnancy
Safe use in children, or pregnant or lactating women has not been established.
Supplied
Not currently available for CPhA monographs. Please consult individual product monographs.
Contraindications
Trihexphenidyl is contraindicated in patients with a known hypersensitivity to trihexyphenidyl or any of its excipients, and in patients with angle-closure glaucoma or severe ulcerative colitis.
Warnings
See Precautions.
Adverse Effects
Genitourinary
Urinary hesitancy or retention.
Gastrointestinal
Dry mouth, constipation, nausea, vomiting. Isolated cases of dilatation of the colon, paralytic ileus and suppurative parotitis secondary to excessive dryness of the mouth have been reported. Dry mouth may be relieved by the use of saliva substitute or sugarless gum.
Endocrine
Hyperthermia, anhidrosis, heat stroke.
Central Nervous System
Dizziness, drowsiness, anxiety, headache. Less frequent reactions include confusion, disturbed behavior, restlessness, delirium, euphoria, delusions and hallucinations (patients with pre-existing dementia may be more susceptible).
Hypersensitivity
Skin rash may occur occasionally.
Musculoskeletal
Weakness.
Ophthalmic
Blurred vision, mydriasis, increased intraocular pressure, cycloplegia, photophobia, xerophthalmia.
Cardiovascular
Tachycardia, postural hypotension, palpitations.
Overdose
Symptoms
Symptoms of trihexyphenidyl overdose are primarily extensions of its anticholinergic actions. Tachycardia; flushed, hot, dry skin; dry mucous membranes; mydriasis and blurred vision are common. Drowsiness, nervousness and lightheadedness may progress to, or alternate with, agitation, confusion, delirium and hallucinations, especially in children or the elderly. Urinary retention, hypertension, hyperthermia, photophobia, thirst and decreased gastrointestinal motility are also seen. Pupils may be fixed. Susceptible patients may experience angle-closure glaucoma. In severely poisoned patients coma or seizures may occur. Psychosis, rash, dystonic reactions, respiratory depression, cardiac arrhythmia and rhabdomyolysis have been reported.
Treatment
Treatment is symptomatic and supportive. If ingestion occurred within 4 hours prior to presentation for medical care, administer activated charcoal with or without a cathartic. Cathartics should not be given to patients with an ileus or impaired renal function. Monitor vital signs, urine output and bowel sounds; monitor ECG in severely poisoned patients. Maintain respiration, fluid and electrolyte balance. Mydriasis and cycloplegia may be treated with a local miotic such as pilocarpine. Hyperthermia can be managed with physical measures and control of agitation. Treat agitation and seizures with i.v. benzodiazepines. Avoid antipsychotics and other anticholinergic drugs. If rhabdomyolysis does occur, alkalinize urine and maintain good urine output. Peritoneal dialysis and hemodialysis are of no value in the management of trihexyphenidyl overdose.
Dosage
Trihexiphenidyl dosage should be individualized. The initial dosage should be low and then increased gradually, especially in patients over 60 years of age.
Parkinsonism: 1 mg orally the first day; increase by 2 mg daily at intervals of 3 to 5 days, up to 6 to 10 mg daily. In patients with post-encephalitic parkinsonism, dosages as high as 12 to 15 mg daily may be necessary. The total daily dose is best tolerated if divided into 3 doses and taken at mealtimes.
Drug-induced Parkinsonian Symptoms: The size and frequency of doses of trihexyphenidyl needed to control drug-induced parkinsonian symptoms, attributable especially to antipsychotics, must be determined empirically. The total daily dosage usually ranges between 5 and 15 mg; however, in some cases, these reactions have been satisfactorily controlled with as little as 1 mg daily. It may be advisable to commence therapy with a single 1 mg dose. If the extrapyramidal manifestations are not controlled in a few hours, the subsequent doses may be progressively increased until satisfactory control is achieved. Control may sometimes be more rapidly achieved by temporarily reducing the dosage of the antipsychotic or instituting trihexyphenidyl therapy and then adjusting the dosage of both drugs until the desired antipsychotic effect is retained without the reappearance of parkinsonian symptoms.
It is sometimes possible to maintain the patient on a reduced trihexyphenidyl dosage after the reactions have remained under control for several days. In the majority of patients, the use of anticholinergic agents is not required after 3 months of antipsychotic therapy.
