Dantrolene has little effect on cardiac and smooth muscle. Clinical benefits may not be gained beyond 100mg per day. The manufacturers recommend a maximum daily dose of 400mg to limit the risk of hepatotoxicity. Dantrolene is licensed for symptomatic treatment of chronic severe spasticity in voluntary muscle. It is generally recommended for treatment of cerebral spasticity, but it is also effective in spinal cord injury.
Muscle weakness induced by dantrolene makes it a poorly tolerated therapy compared to baclofen.
In clinical practice, dantrolene is most suited to patients with good muscle strength who are limited by their spasticity, or those with complete paralysis, such as paraplegics. Tizanidine is the first new antispastic agent to be licensed in over 20 years. Although it inhibits spinal polysynaptic reflex activity, the mechanism of action has not yet been clarified. The effects of tizanidine are mainly related to its central a2-adrenoceptor agonist properties, but effects on the imidazole receptor may also be involved. It is recommended that tizanidine should be introduced at a dose of 2mg at bedtime and gradually titrated upwards over four to seven weeks.