Tripar tablet is indicated as an adjunct in the treatment of all forms of parkinsonism, including postencephalitic, arteriosclerotic, and idiopathic types. It is often used as an adjuvant therapy in combination with levodopa for the management of Parkinsonism. It is also indicated for the control of extrapyramidal symptoms caused by central nervous system drugs such as dibenzoxazepines, phenothiazines, thioxanthenes, and butyrophenones.

Trihexyphenidyl exerts a direct inhibitory effect on the parasympathetic nervous system. It also produces a relaxing effect on smooth muscles, both through a direct action on muscle tissue and indirectly via inhibition of the parasympathetic nervous system.

Trihexyphenidyl is a non-selective muscarinic acetylcholine receptor antagonist with higher affinity for the M1 subtype. In vivo studies show greater affinity for central muscarinic receptors in the cerebral cortex and lower affinity for peripheral receptors. It may also influence nicotinic acetylcholine receptor neurotransmission, indirectly increasing dopamine release in the striatum. Although widely used in Parkinson’s disease and movement disorders, its exact mechanism of action is not fully understood.

The dosage of Trihexyphenidyl should be individualized. Treatment is usually started with a low dose and gradually increased, especially in patients over 60 years of age. The timing of administration (before or after meals) should be adjusted based on patient response. Patients with postencephalitic parkinsonism, who often experience excessive salivation, may prefer taking the medicine after meals, and may sometimes require small doses of atropine as an adjuvant. If dry mouth becomes troublesome, taking the dose before meals may be better, unless it causes nausea. When taken after meals, thirst can be relieved with water, mint candies, or chewing gum. Abrupt discontinuation of Trihexyphenidyl should be avoided, as it may lead to worsening of Parkinsonism symptoms or, in rare cases, neuroleptic malignant syndrome (NMS).

Idiopathic Parkinsonism: Initial therapy starts with 1 mg on the first day. The dose may be increased by 2 mg every 3–5 days until a total daily dose of 6–10 mg is reached. Some patients, especially postencephalitic cases, may require 12–15 mg daily.

Drug-induced Parkinsonism: Dose is individualized, usually ranging from 5–15 mg daily, though some patients may respond to as little as 1 mg daily. Treatment may start with 1 mg and gradually increased until symptoms are controlled.

Concomitant use with Levodopa: When used with levodopa, doses of both drugs may need to be reduced. Careful adjustment is required based on symptom control and side effects. A total daily dose of 3–6 mg in divided doses is often sufficient.

Use with other parasympathetic inhibitors: Trihexyphenidyl may partially or fully replace other anticholinergic drugs, with gradual dose adjustment. The total daily dose is best tolerated when divided into 3 doses taken with meals. If the dose exceeds 10 mg daily, it may be divided into 3 doses with meals and an additional dose at bedtime.

Pediatric use: Safety and effectiveness in children have not been established.

Trihexyphenidyl is contraindicated in patients with hypersensitivity to the drug. It is also contraindicated in narrow-angle glaucoma. Long-term use has been associated with blindness due to worsening of glaucoma.

Common side effects (30–50%) include dry mouth, blurred vision, dizziness, mild nausea, and nervousness. These are usually less severe than with belladonna alkaloids and may reduce over time. Rare effects include parotitis, skin rash, constipation, paralytic ileus, psychiatric symptoms such as hallucinations, delusions, and paranoia. Other possible effects include confusion, memory impairment, urinary retention, tachycardia, increased intraocular pressure, weakness, vomiting, headache, choreiform movements, and drowsiness. Abrupt withdrawal may worsen parkinsonism or cause neuroleptic malignant syndrome. Pediatric cases may include hyperkinesia, psychosis, weight loss, and sleep disturbances.

Use during pregnancy should only be considered if clearly needed and benefits outweigh risks. It is unknown whether the drug passes into breast milk. It may suppress lactation; therefore, caution is advised during breastfeeding.

Patients should be evaluated for glaucoma risk before starting treatment. It may increase intraocular pressure and cause angle-closure glaucoma. Use with caution in hot weather and in patients exposed to heat or dehydration. Severe sweating impairment may lead to hyperthermia, which can be fatal. Neuroleptic Malignant Syndrome may occur during dose reduction or withdrawal.

In humans, doses up to 300 mg (5 mg/kg) have been reported without fatalities or long-term sequelae. However, rare cases of death have occurred when Trihexyphenidyl overdose was taken together with other CNS depressant agents or in patients with compromised respiratory function. Blood concentrations associated with fatal cases ranged from 0.03 to 0.80 mg/L.

Signs and Symptoms: Overdose produces central anticholinergic (atropine-like) toxicity. Diagnosis is based on peripheral parasympathetic blockade signs such as dilated and sluggish pupils, warm dry skin, facial flushing, decreased secretions of the mouth, nose, pharynx, and bronchi, fever, tachycardia, cardiac arrhythmias, reduced bowel sounds, and urinary retention. Neuropsychiatric manifestations may include delirium, confusion, anxiety, hallucinations, agitation, hyperactivity, memory loss, paranoia, seizures, and ataxia. Severe cases may progress to stupor, coma, respiratory failure, cardiac arrest, and death.

Treatment :Management of acute overdose is mainly supportive and symptomatic. Gastric lavage or other methods to reduce absorption should be considered. Low-dose diazepam or short-acting barbiturates may be administered if CNS excitation occurs. Phenothiazines are contraindicated due to increased risk of toxicity. Respiratory support, artificial ventilation, or vasopressor agents may be required. Hyperthermia should be managed promptly, fluids replaced, and acid–base balance maintained. Urinary catheterization may be necessary. The dialyzability of Trihexyphenidyl is unknown.

Antiparkinson drugs

Store at a temperature not exceeding 30°C in a dry place. Protect from light.