Trihexyphenidyl Hydrochloride is indicated as an adjunct treatment of all forms of parkinsonism (postencephalitic, arteriosclerotic & idiopathic). Additionally, it is indicated for the control of extrapyramidal disorders caused by central nervous system drugs such as dibenzoxazepines, phenothiazines, thioxanthenes & butyrophenones.

Antiparkinson drugs

Trihexyphenidyl is a selective M1 muscarinic acetylcholine receptor antagonist. It is able to discriminate between the M1 (cortical or neuronal) and the peripheral muscarinic subtypes (cardiac and glandular). Trihexyphenidyl partially blocks cholinergic activity in the CNS, which is responsible for the symptoms of Parkinson’s disease. It is also thought to increase the availability of dopamine, a brain chemical that is critical in the initiation and smooth control of voluntary muscle movement.

Dosage should be individualized. The initial dose should be low and then increased gradually, especially in patients over 60 years of age. Whether Trihexyphenidyl may best be given before or after meals should be determined by the way the patient reacts.

Idiopathic Parkinsonism: 1 mg of Trihexyphenidyl may be administered the first day. The dose may then be increased by 2 mg increments at intervals of three to five days.

Drug-Induced Parkinsonism: Commence therapy with a single 1 mg dose increase the total daily dosage to 5-15 mg range if the extrapyramidal manifestations are not controlled.

Concomitant Use with Levodopa: When Trihexyphenidyl is used concomitantly with levodopa, the usual dose is 3-6 mg daily.

Cannabinoids, barbiturates, opiates, and alcohol may have additive effects with trihexyphenidyl, and thus, an abuse potential exists. Concurrent use of alcohol or other CNS depressants with trihexyphenidyl may cause increased sedative effects. It may be contraindicated in patients taking monoamine oxidase inhibitors & tricycllic antidepressants.

Trihexyphenidyl is contraindicated in patients with hypersensitivity in patients to trihexyphenidyl HCl or to any of the tablet or elixir ingredients. Trihexyphenidyl is also contraindicated in patients with narrow angle glaucoma. Blindness after long-term use due to narrow angle glaucoma has been reported.

Minor side effects such as dryness of the mouth, blurring of vision, dizziness, mild nausea or nervousness. Patients with arteriosclerosis or with a history of idiosyncrasy to other drugs may exhibit reactions of mental confusion, agitation, disturbed behavior, or nausea and vomiting. Potential side effects are constipation, drowsiness, urinary hesitancy or retention, pupil dilation, increased intraocular tension, vomiting and headache.

Pregnancy Category C. It is not known whether the drug is excreted in human milk and therefore trihexyphenidyl should only be used if the expected benefit to the mother outweighs the potential risk to the infant.

Patients with cardiac, liver, or kidney disorders, or with hypertensioon, should closely be monitored. Since trihexyphenidyl has parasympatholytic activity, it should be used with caution in patients with glaucoma, obstructive disease of the gastrointestinal or genitourinary tracts, and in elderly males with possible prostatic hypertrophy. Trihexyphenidyl is not recommended for use in patients with tardive dyskinesia unless they have concomitant Parkinson’s disease. Abrupt withdrawal of treatment for parkinsonism may result in acute exacerbation of parkinsonism symptoms; therefore, abrupt withdrawal should be avoided.

Overdosage with trihexyphenidyl produces typical central symptoms of atropine intoxication ( the central anticholinergic syndrome). Signs & symptoms are: dilated and sluggish pupils, warm, dry skin, facial flushing, decreased secretions of mouth, pharynx, nose and bronchi, foul smelling breath, tachycardia etc. Neuropsychiatric signs such as delirium, disorientation, anxiety, hallucinations etc. The condition can progress to stupor, coma, paralysis, cardiac, respiratory arrest and death.