Pediatric Safety of Tizanidine

Objective: To evaluate the safety of tizanidine in the pediatric population.

Methods: We compared spontaneous adverse event reports in the Acorda Therapeutics worldwide clinical adverse event database for children (≤16 years; n = 99) and adults (>16 years; n= 1153) who had received tizanidine and for whom at least one adverse event was reported, and performed a retrospective chart review of the safety of tizanidine in children (≤16 years; n = 76) at a large US pediatric neurology practice. Causality of adverse events in our worldwide clinical adverse event database were neither assessed nor assigned by the company.

Results: When adverse events from the clinical adverse event database were collapsed into the 25 Medical Dictionary for Regulatory Activities (MedDRA; version 9.0) organ system classes, five classes were more frequent in adults (general disorders and administration site conditions [p = 0.0006], hepatobiliary disorders [p = 0.0031], nervous system disorders [p = 0.0108], skin and subcutaneous disorders [p = 0.0063], and vascular disorders [p = 0.0029]), while one class was more frequent in children (psychiatric disorders [p < 0.0001]). The most common adverse event classes in children were psychiatric disorders (52.5%) followed by nervous system disorders (29.3%), and gastrointestinal disorders (16.2%), whereas the most common adverse event classes in adults were nervous system disorders (42.4%), general disorders and administration site conditions (28.6%), and gastrointestinal disorders (21.3%). Serious adverse events were substantially less frequent in children than adults (19.2% vs 45.9%) in the clinical adverse event database. In the pediatric practice chart review, the incidence of adverse events in the MedDRA psychiatric disorders class was very similar (52.6%) to that for children in the clinical adverse event database, while the next most common classes were gastrointestinal disorders (14.5%), and nervous system disorders (13.2%). There were three deaths in children across the databases, including one from accidental exposure and two from cardiac events; the relationship of cardiac events in relation to tizanidine or other causes was difficult to assess with the limited available information. The major causes of death in adults were related to suicide or overdose. Minor, transient liver transaminase increases were occasionally reported; the effect of tizanidine could not be ruled out.

Conclusion: The overall safety of tizanidine in the pediatric group appeared good; however, the adverse event profile differed from that in adults. This difference most likely reflects the off-label use of tizanidine as adjunctive treatment for attention disorders and autism. The frequency and nature of adverse events in adults were consistent with the tizanidine prescribing information as reported for its approved indication, i.e. management of spasticity.