Tizanidine was evaluated in a prospective, double-blind, randomized, placebo-controlled trial in 187 patients with MS. Taken orally for 9 weeks and preceded by a titration phase for a period of 3 weeks starting at 2 mg daily, tizanidine produced a significant reduction in spastic muscle tone compared with placebo treatment. Within the effective dose range of 24 to 36 mg given daily in three doses, tizanidine achieved a 20% mean reduction in muscle tone. Approximately 75% of patients, with all degrees of spasticity, reported subjective improvement without an increase in muscle weakness, but there was no improvement in activities of daily living depending on movement. Tizanidine achieved its maximum effect on spasticity within 1 week of the start of treatment; the benefit was maintained for at least 1 week after discontinuation of therapy. A variety of adverse events was recorded by patients taking tizanidine, but these were minor and reversible, and rarely limited treatment. Tizanidine is a well-tolerated and effective drug for symptomatic treatment of spasticity.

Data from three placebo-controlled and 11 active-controlled studies of tizanidine were combined to permit analysis of the subsets, which were too small to evaluate within the individual studies. Overall analysis of placebo-controlled data confirms the effectiveness of tizanidine in reducing muscle tone in patients with spasticity of spinal cord origin. Subset analyses suggest that patients with more severe spasticity are more likely to respond, but age, sex, and race were not predictive of response. Comparisons of tizanidine with active controls showed no differences in efficacy compared with baclofen or diazepam. However, when compared with controls, patients treated with tizanidine did not experience increased weakness. Furthermore, patients tolerated tizanidine better than the control medications. More patients experienced adverse events during tizanidine treatment than did patients receiving placebo. The most common adverse events reported were dry mouth, somnolence, asthenia, and dizziness. Mild elevations in liver function tests were noted occasionally, but improved in all patients with dose reduction or withdrawal. Three patients from the double-blind database reported formed visual hallucinations. All three cleared; two continued tizanidine, and one discontinued.

Pharmacologic and electrophysiologic studies over the past 20 years have shown tizanidine to be a potent, central-acting myotonolytic agent that principally affects spinal polysynaptic reflexes. This action arises from agonistic activity of the compound at noradrenergic alpha 2 receptors, resulting in both direct impairment of excitatory amino acid release from spinal interneurons and a concomitant inhibition of facilitatory coeruleospinal pathways. Similar alpha 2-receptor-mediated inhibition of interneuronal activity appears to underlie the additional antinociceptive and anticonvulsant activity of tizanidine reported in several species and test paradigms. Despite its structural and biochemical similarity to clonidine, the cardiovscular properties of tizanidine are mild and transitory in relation to its activity as a muscle relaxant. These findings, together with a possible greater separation between myotonolytic and general CNS depressant activity than with other agents, make tizanidine a valuable addition in the pharmacologic treatment of spasticity.