Utilization of zonisamide in patients with chronic pain or epilepsy refractory to other treatments: a retrospective, open label, uncontrolled study in a VA hospital

Objectives: Zonisamide (1,2-benzisoxazole-3-methanesulfonamide) is a novel antiseizure medication approved for use in the United States as adjunct therapy in the treatment of partial seizures in adults with epilepsy. It has also been used to treat other conditions including intractable pain. The aim of this study was to determine the usefulness of zonisamide in patients whose seizures were not controlled after having been treated with at least three other currently available anticonvulsant medications or in patients whose pain control was suboptimal despite the use of commonly used drug regimens. Methods: This was a retrospective study documenting the efficacy of zonisamide in 48 consecutive patients who presented at an outpatient neurology clinic at a Veterans Administration hospital. The patients were diagnosed with refractory partial seizures (n = 21) or a variety of intractable neuropathic pain syndromes (n = 27). Results: Sixteen out of 21 seizure patients (76%) experienced a 50% or greater reduction in seizure frequency when zonisamide (1100-200 mg daily) was added to their existing anticonvulsant medication regimen. Of 27 patients with neuropathic pain, 17 (59%) responded to zonisamide, reporting subjective reduction in pain by at least 50%. The most common adverse events were gastrointestinal upset, somnolence, and one case of skin rash. Conclusions: In this study, zonisamide appeared to be an effective adjunct therapy in the treatment of partial seizures in adults who continued to experience frequent episodes while taking other anticonvulsant medications, and in adults whose neuropathic pain was not well controlled with analgesics. These promising results must be tempered by the fact that this investigation included a small patient population in an uncontrolled study design. Further research into the efficacy and tolerability of zonisamide in these areas is warranted.