Trihexiphenidyl

Trihexyphenidyl

Mechanism :

Trihexyphenidyl exerts a direct inhibitory effect upon the parasympathetic nervous system. It also has a relaxing effect on smooth musculature; exerted both directly upon the muscle tissue itself and indirectly through an inhibitory effect upon the parasympathetic nervous system. Its therapeutic properties are similar to those of atropine although undesirable side effects are ordinarily less frequent and severe than with the latter.

Indication :

• Antispasmodic
• Dystonia
• Extrapyramidal symptoms

Contraindications :

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

Dosing :

>2 years: Start with 1 mg PO twice a day, after 7 days increase by 1-2 mg/day every 3-4 days till maintenance of 6-40 mg/day till max dose of 100 mg/day.

Adverse Effect :

Side effects are due to anticholinergic and antimuscarinic effects. Tachycardia. constipation, paralytic ileus, dry mouth, nausea, vomiting, confusion, psychosis, visual hallucinations, memory impairment, depression, blurred vision, dilated pupils, urinary retention, dysuria, hypersensitivity, rash.

Interaction :

Nefopam, Disopyramide, Tricyclic Anti-Depressants, MAOIs, Antihistamines and Phenothiazines: Increased antimuscarinic effects blurred vision, dry mouth, constipation and urinary retention.
MAOIs, Amantadine and some Tricyclic Antidepressants: May also cause excitation, confusion and hallucinations.
Ketoconazole and Levodopa: Reduces absorption of ketoconazole and levodopa.
Cisapride: Antagonises.

Hepatic Dose :