Trihexy 2

Indications

Trihexyphenidyl is commonly prescribed as an adjunct therapy for various forms of parkinsonism, including postencephalitic, arteriosclerotic, and idiopathic types. It is often recommended alongside levodopa for more effective management of Parkinson’s disease. Additionally, Trihexyphenidyl is beneficial in controlling extrapyramidal symptoms caused by central nervous system medications such as dibenzoxazepines, phenothiazines, thioxanthenes, and butyrophenones.
Note: Always consult a registered healthcare professional before using this medication.

Description

Trihexyphenidyl works by directly inhibiting the parasympathetic nervous system and has a relaxing effect on smooth muscle tissue. This effect is achieved both directly on muscle fibers and indirectly through its impact on the parasympathetic nervous system.

Pharmacology

Trihexyphenidyl is a non-selective muscarinic acetylcholine receptor antagonist, primarily binding to the M1 subtype. Studies suggest that it has a stronger affinity for central muscarinic receptors in the cerebral cortex, while its binding to peripheral receptors is weaker. Furthermore, it may influence nicotinic acetylcholine receptors, leading to increased dopamine release in the striatum. Although its precise mechanism of action remains unclear, Trihexyphenidyl is effective in treating Parkinson’s disease and related movement disorders.

Dosage & Administration

The dosage of Trihexyphenidyl should be tailored to each patient. Start with a low dose and increase gradually, particularly for patients over the age of 60. The timing of administration, whether before or after meals, should be adjusted based on individual responses. In postencephalitic patients, it may be preferable to take the medication after meals to reduce excessive salivation. If dry mouth occurs, the dose may be taken before meals to help mitigate this effect.

• Idiopathic Parkinsonism: Begin with 1 mg on the first day, gradually increasing the dose by 2 mg every 3-5 days until the optimal dose of 6-10 mg daily is reached. In some cases, postencephalitic patients may require a total daily dose of 12-15 mg.
• Drug-Induced Parkinsonism: Initial dosing should start at 1 mg, with subsequent increases based on the patient’s response. A typical daily dose ranges from 5 to 15 mg.
• Concomitant Use with Levodopa: If used with levodopa, doses of both medications may need to be adjusted. Typically, 3-6 mg of Trihexyphenidyl daily is sufficient.
• Concomitant Use with Other Parasympathetic Inhibitors: Trihexyphenidyl can be substituted for other parasympathetic inhibitors, starting with partial substitution, and gradually adjusting the doses of both medications.

Use in Children

The safety and effectiveness of Trihexyphenidyl in pediatric patients have not been established.
Note: Always follow a healthcare provider’s instructions.

Drug Interactions

Trihexyphenidyl may interact with cannabinoids, barbiturates, opiates, and alcohol, leading to additive sedative effects. Combining Trihexyphenidyl with alcohol or other CNS depressants can intensify sedative effects. Anticholinergic medications like MAO inhibitors and tricyclic antidepressants may enhance the anticholinergic effects of Trihexyphenidyl.

Contraindications

Trihexyphenidyl is contraindicated in patients who are hypersensitive to the drug or those with narrow-angle glaucoma, as it may lead to increased intraocular pressure and blindness in severe cases.

Side Effects

Common side effects include dry mouth, blurred vision, dizziness, mild nausea, and nervousness, which typically occur in 30-50% of patients. These symptoms often subside as treatment continues. Severe reactions such as cognitive dysfunction, constipation, tachycardia, increased intraocular pressure, and psychiatric symptoms (e.g., hallucinations, paranoia) have been reported in rare cases. Abrupt discontinuation of Trihexyphenidyl may exacerbate Parkinsonism symptoms or lead to neuroleptic malignant syndrome (NMS).

Pregnancy & Lactation

There are no controlled studies regarding the use of Trihexyphenidyl during pregnancy. It should only be used during pregnancy if the benefits outweigh the risks. It is unknown whether Trihexyphenidyl is excreted in breast milk, so caution is advised when administering this drug to nursing mothers. Like other anticholinergics, Trihexyphenidyl may suppress lactation.

Precautions & Warnings

Before starting Trihexyphenidyl, patients should undergo a gonioscope evaluation, and intraocular pressures should be monitored regularly. The use of anticholinergics can precipitate angle-closure glaucoma and increase intraocular pressure. Trihexyphenidyl should be used cautiously in hot climates or by individuals who are prone to sweating disturbances, as it may impair the body’s ability to regulate temperature.

Overdose Effects

Trihexyphenidyl overdose symptoms include typical signs of atropine intoxication, such as dry skin, elevated heart rate, dilated pupils, urinary retention, and confusion. Overdose can lead to severe outcomes like delirium, seizures, coma, and even death. Treatment involves symptomatic care, gastric lavage, and the use of supportive measures such as respiratory support and fluid replacement.

Therapeutic Class

Antiparkinsonian Medications

Storage Conditions

Store Trihexyphenidyl in a dry place at temperatures not exceeding 30°C. Protect from light to maintain the drug’s effectiveness.