Antimuscarinic agents are used in parkinson's disease (idiopathic or primary parkinsonism) and drug - induced Parkinsonism. Those commonly used are the tertiary amine, benzhexol hydrochloride, benztropine mesylate, orphenadrine hydrochloride, and procyclidine hydrochloride.

In Parkinson's disease, antimuscarinics are generally used in the early stages when the condition is mild and tremor is the predominant symptom as they provide little benefit in bradykinesia. They can also reduce the diarrhoea experienced by patients with this disease.

Antimuscarinics are also used as adjuvant therapy with levodopa plus adopa - decarboxylase inhibitor to reduce or prevent levodopa - induced adverse effects including the "on - off" phenomenon.

Tardive dyskinesia is not improved by the antimuscarinic drugs and may be made worse.

Benzhexol (Trihexyphenidyl Hydrochloride)
Tablet, 2mg, 5mg

Indications: - Parkinsonism; drug induced extrapyramidal symptoms (but not tardive dyskinesia).

Cautions: - as antimuscarinics in general (see section 1.3), and cardiovascular disease, hepatic or renal impairment; elderly, avoid abrupt discontinuation of treatment; liable to abuse (may produce euphoric effect); interactions

Drug interactions, Side effects: - as antimuscarinics in general (see section 1.3)

Contraindications: - untreated urinary retention, angle-closure glaucoma, gastrointestinal obstruction.

Dose and Administration

1 mg daily, increased gradually; usual maintenance dose 5 - 15mg daily in 3 - 4 divided doses; elderly preferably lower end of range.

Storage: - at room temperature in a tight container.

Benztropine (Mesylate)
Tablet, 2mg
Injection, 1mg/ml in 2ml ampoule

Indications, Caution, Drug interactions; see Trihexyphenidyl hydrochloride

Side effects: see trihexypenidyl Hydrochloride, but causes sedation rather than stimulation.

Contraindications: see Trihexyphenidyl Hydrochloride; avoid in children less than 3 years.

Dose and Administration:

By mouth, 0.5 - 1mg daily usually at bedtime, generally increased, max. 6mg daily; usual maintenance dose 1 - 4mg daily in single or divided dose; elderly preferably lower end of range.

By intramuscular or intravenous injection, 1 - 2mg repeated if symptoms reappear; Elderly preferably lower end of range.

Storage: - at room temperature in a well-closed container. Protect from freezing.