Alert on Metabolic Acidosis from Zonisamide (Zonegran)

FDA has alerted healthcare professionals that the drug zonisamide can cause metabolic acidosis in some patients. Zonisamide is marketed as Zonegran and in generic form. It is used as an adjunctive therapy in treating partial seizures in adults with epilepsy. Zonisamide is not approved for pediatric use.

Zonisamide-induced metabolic acidosis is characterized by hyperchloremia and decreased serum bicarbonate. It generally occurs early in treatment, but can also arise later. The risk appears to be increased in those taking high doses of the drug, but acidosis has been observed with doses as low as 25 mg daily. Patients at higher risk also include those with renal disease, severe respiratory disorders, diarrhea and a ketogenic diet, as well as those taking certain other drugs. Children are also at higher risk. Note that zonisamide can be passed to nursing infants through the breast milk of mothers taking the drug.

Although patients with persistent metabolic acidosis may exhibit symptoms such as hyperventilation, fatigue, anorexia and cardiac arrhythmias, they are often asymptomatic. If left untreated, metabolic acidosis may increase the risk of kidney stones, nephrocalcinosis and bone abnormalities, and it can reduce growth rates in children and affect fetal development.

Here are FDA's recommendations for healthcare professionals:

• Measure serum bicarbonate before starting zonisamide treatment and periodically thereafter, even in the absence of symptoms.

• If metabolic acidosis develops and persists, consider either reducing the dose or discontinuing the drug and modifying the patient's anti-epileptic treatment.

• If a patient with metabolic acidosis is to continue on zonisamide, consider treatment with alkali.

FDA Patient Safety News: May 2009

For more information, please see our website:
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/psn/transcript.cfm?show=86#6

Category:

Education

Tags:

• Zonisamide
• Zonegran
• epilepsy
• seizures
• side effect
• drug
• metabolic acidosis
• FDA

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