The central alpha 2
adrenoceptor agonist
tizanidine is a myotonolytic agent used in the treatment of spasticity in patients with cerebral or
spinal injury. Wide interpatient variability in the effective plasma concentrations of
tizanidine means that the optimal dosage must be titrated over 2 to 4 weeks for each patient (dosages of 2 to 36 mg/day have been used in clinical trials). Maximum effects occur within 2 hours of administration. Antispastic efficacy has been demonstrated for
tizanidine in placebo-controlled trials, with reduction in mean muscle tone scores of 21 to 37% versus 4 to 9% for patients receiving placebo. Improvement in muscle tone occurred in 60 to 82% of
tizanidine recipients, compared with 60 to 65% of
baclofen and 60 to 83% of
diazepam recipients.
Spasm frequency and clonus are also reduced by
tizanidine. The most common adverse effects associated with
tizanidine are dry mouth and
somnolence/drowsiness. Muscle strength, as assessed by objective means, appears not to be adversely affected by
tizanidine and subjective
muscle weakness is reported less often by
tizanidine recipients than by those receiving
baclofen or
diazepam. Global tolerability was assessed as good to excellent in 44 to 100% of patients receiving
tizanidine, compared with 38 to 90% of
baclofen and 20 to 54% of
diazepam recipients. In conclusion,
tizanidine is an antispastic agent with similar efficacy to that of
baclofen and a more favourable tolerability profile. While drowsiness is a frequently reported adverse effect with both agents, subjective
muscle weakness appears to be less of a problem with
tizanidine than with
baclofen.
Tizanidine, therefore, appears to be an attractive therapeutic alternative for patients with spasticity associated with cerebral or spinal damage.