A Cochrane review [Abstract] 1 included 5 studies with a total of 949 subjects with with drug-resistant partial epilepsy. They were all placebo-controlled parallel-group trials with a stable-dose phase of 12 or 18 weeks. The overall RR 50% reduction in seizure frequency compared to placebo for 300 to 500 mg/day of zonisamide was 2.00 (95% CI 1.58 to 2.54; 5 trials, n=891). The RR for 50% reduction in seizure frequency compared to placebo for any dose of zonisamide (100 to 500 mg per day) was 1.92 (95% CI 1.52 to 2.42; 5 trials, n=949). The NNT was 6 for this outcome. The RR for treatment withdrawal for 300 to 500 mg/day of zonisamide compared to placebo was 1.64 (95% CI 1.20 to 2.25; 5 trials, n=892) and for 100 to 500 mg per day was 1.47 (95% CI 1.07 to 2.01; 5 trials, n=949). NNT for this outcome was 21. The CIs of the following adverse effects indicate that they are significantly associated with zonisamide: ataxia 3.77 (99% CI 1.28 to 11.11); somnolence 1.83 (99% CI 1.08 to 3.11); agitation 2.35 (99% CI 1.05 to 5.27) and anorexia 2.71 (99% CI 1.29 to 5.69).
Comment: The quality of the evidence is downgraded by indirectness (short follow-up time).
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