Indications: chronic severe spasticity of voluntary muscle; malignant hyperthermia.

Cautions: impaired cardiac and pulmonary function; therapeutic effect may take a few weeks to develop— discontinue if no response within 6–8 weeks.

Note: Drowsiness may affect performance of skilled tasks (e.g. driving); effects of alcohol enhanced.

Contra-indications: acute muscle spasm; avoid when spasticity is useful, for example, locomotion.

Side Effects: Hepatotoxicity. Potentially life-threatening hepatotoxicity reported, usually if doses greater than 400 mg daily used, in females, patients over 30 years, if history of liver disorders, or concomitant use of hepatotoxic drugs; test liver function before and at intervals during therapy—discontinue if abnormal liver function tests or symptoms of liver disorder diarrhoea (withdraw if severe, discontinue treatment if recurs on re- introduction), nausea, vomiting, anorexia abdominal pain; pericarditis; pleural effusion, respiratory depression; headache, drowsiness, dizziness, asthenia, fatigue, seizures, fever, chills; speech and visual disturbances.

Dose: Initially 25 mg daily, may be increased at weekly intervals to max. 100 mg 4 times daily; usual dose 75 mg 3 times daily.