The epilepsy drug zonisamide, sold both generically and under the brand name Zonegran, can cause a serious blood disorder called metabolic acidosis, the Food & Drug Administration (FDA) warned today. The agency said it is working with the makers of zonisamide to revise the product labeling to reflect this new risk.
According to the FDA, metabolic acidosis is a disturbance in the body’s acid-base balance that results in excessive acidity of the blood. Metabolic acidosis can result in hyperventilation, and non-specific symptoms such as fatigue and anorexia, or more severe symptoms including cardiac arrhythmias or stupor. Chronic metabolic acidosis can have adverse effects on the kidneys and on bones, and can retard growth in children.
Patients with predisposing conditions or therapies, including renal disease, severe respiratory disorders, diarrhea, surgery, ketogenic diet, or certain other drugs may be at greater risk for developing metabolic acidosis following treatment with zonisamide. The risk of zonisamide-induced metabolic acidosis appears to be more frequent and severe in pediatric patients, the FDA said.
According to a review of updated clinical data, the development of metabolic acidosis in patients taking Zonegran and generic equivalents generally appears to be dose-dependent and can occur at doses as low as 25 mg daily, the FDA said. Zonegran-induced metabolic acidosis generally occurs early in treatment, although it can occur at anytime.
The FDA has recommended that healthcare professionals measure serum bicarbonate before starting treatment and periodically during treatment with Zonegran, even in the absence of symptoms. If metabolic acidosis develops and persists, consideration should be given to reducing the dose or discontinuing Zonegran, and modifying the patient’s antiepileptic treatment as appropriate. If metabolic acidosis develops and persists, consideration should be given to reducing the dose or discontinuing Zonegran, and modifying the patient’s antiepileptic treatment as appropriate.
If the decision is made to continue patients with metabolic acidosis on Zonegran, then alkali treatment should be considered, the FDA said.
Zonisamide is approved as an adjunct therapy to treat partial seizures in adults. It is sold as Zonegran by Eisai Co Ltd, and in generic form by Teva Pharmaceutical Industries Ltd., Mylan Inc., Novartis AG’s Sandoz unit and Watson Pharmaceuticals Inc.
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