Zonegran or Zonisamide is one of the newer anti-epiletic drugs (AEDs). It comes as a single sized tablet of 100 mg. The medication has a very long half-life (measured in days, not hours) and therefore appropriate for one time daily dosing. It is the only new AED that is indicated for once daily dosing.
The medication has multiple mechanisms of action, the relative importance of each to its anti-epileptic effect is not known. Mechanisms include blocking sodium (Na+) channels, reducing voltage-dependent, transient inward T-type calcium (Ca++) channels, increasing GABA release, blocking potassium (K+) evoked glutamate-mediated synaptic excitation, and weakly inhibiting carbonic anhydrase.
It is considered effective in partial onset seizures. It does not appear to cause any bone marrow problems. Its incidence of liver toxicity is much lower than the older AEDs. It can cause renal stones. It is in the sulfa family of drugs and therefore should not be used by patients allergic to sulfa drugs. The medication should be discontinued in patients who develop a rash. The medication does not interfere with birth control pills. Its safety in pregnancy is not known. There are drug interactions with other AEDs.
In open label trials, Zonegran® has been shown effective in reducing the number of migraines. In open label add on trials, Zonegran® has been shown to be effective in some forms of neuropathic pain.A very exciting recent placebo-controlled trial published in JAMA April 9, 2003 issue by Kishore Gadde, M.D. et. al., demonstrated a significant weight loss in obese patients taking zonegran at a dose of at least 400 mg per day. At 32 weeks, the average patient demonstrated a 9.4% weight loss. They lost on average 4 inches in the waist. Patients lost weight in weeks 16 to 32 (although at a slower rate than weeks 0- 16 ) so the final weight loss is not known. This data adds to other data seen in epilepsy patients which found weight loss as well. At least one study suggested that females were more likely to lose weight than males.
Zonegran® is available in generic form and has at least 6 different manufacturers. Unfortunately, this author has had a number of patients who were doing well on trade name Zonegran® then run into problems with generic zonisamide. In general, increasing the dose by one tablet per day has solved the problem.
Zonegran® has been used by psychiatrists as a mood stabilizing medication. This topic is beyond the scope of this web site.