Dantrolene sodium: a review of its pharmacological properties and therapeutic efficacy in spasticity.

Dantrolene sodium or dantrolene1 is 1([5-(nitrophenyl)furfurylidend] amino) hydantoin sodium hydrate. It is indicated for use in chronic disorders characterised by skeletal muscle spasticity, such as spinal cord injury, stroke, cerebral palsy and multiple sclerosis. Dantrolene is believed to act directly on the contractile mechanism of skeletal muscle to decrease the force of contraction in the absence of any demonstrated effects on neural pathways, on the neuromuscular junction, or on the excitable properties of the muscle fibre membranes. Controlled trials have demonstrated that dantrolene is superior to placebo in adults or children with spasticity from various causes, as evidenced by clinical assessments of disability and daily activities, and by muscle and reflex responses to mechanical and electrical stimulation. It is somewhat less effective in patients with multiple sclerosis than in those with spasticity from other causes. There has been a general clinical impression in controlled trials that dantrolene caused less sedation than would have been expected from therapeutically comparable doses of diazepam. In 2 controlled trials, there was no significant difference between dantrolene and diazepam in terms of reductions in spasticity, clonus, and hyperreflexia, but side-effects such as drowsiness and inco-ordination occurred significantly more frequently on diazepam. Long-term studies have indicated continuing benefit for patients taking dantrolene, though the incidence of side-effects has often been high and there has been a suggestion of exacerbation of seizures in children with cerebral palsy. Dantrolene may be of value in the medical treatment of spasm of the external urethral sphincter due to neurological and non-neurological disease, and animal studies suggest a potential use in the management of malignant hyperpyrexia. Chemical evidence of liver dysfunction may occur in 0.7 to 1% of patients on long-term treatment with dantrolene, with symptomatic hepatitis in 0.35 to 0.5% and fatal hepatitis in 0.1 to 0.2%. The drug commonly causes transient drowsiness, dizziness, weakness, general malaise, fatigue and diarrhoea at the start of therapy. Muscle weakness may be the principal limiting side-effect in ambulant patients, particularly in those with multiple sclerosis, and therapy could be hazardous in patients with pre-existing bulbar or respiratory weakness. The dosage of dantrolene has been fixed in most controlled trials, though long-term studies have indicated the need for individualisation of dosage. The initial dose is usually 25mg once daily, increasing to 25mg two, three or four times daily, and then by increments of 25mg up to as high as 100mg two, three or four times daily. The lowest dose compatible with optimal response is recommended.