Zonegran Side Effects May Cause Chemical Imbalances in the Blood: FDA

The FDA has issued an alert to notify healthcare professionals that Zonegran, which is also available as generic zonisamide, can cause metabolic acidosis side effects in some patients. This blood disorder could have an adverse effect on the kidneys and bones, and may retard growth in children.

Zonegran is the brand name for zonisamide, which is an epilepsy drug approved as an adjunctive therapy for treatment of partial seizures in epileptic adults. While it is not approved for use in children, as a monotherapy for epilepsy in adults, or for migraine prophylaxis in adults, it is often used off-label for these purposes.

Following an updated review of clinical data for the medication, the FDA issued an alert on February 23, 2009, indicating that they are working with the drug’s makers to update the product labeling about potential zonisamide side effects which could cause excessive acidity of the blood from metabolic acidosis.

The FDA indicates that certain individuals may be more likely to develop Zonegran metabolic acidosis side effects, such as those with kidney disease, severe lung disorders, diarrhea, those who have undergone surgery, or those who follow a ketogenic diet.

The risk of metabolic acidosis also appears to be more frequent and severe in children, for whom the drug is not approved.

Metabolic acidosis causes excess acidity of the blood with elevated chloride ion levels and reduced levels of serum bicarbonate. It is caused by a chemical imbalance in the body’s acid base levels.

As a result of the chemical imbalance, it may produce symptoms like hyperventilation, fatigue, anorexia or irregular heart rhythms. Chronic cases may result in bone defects, kidney stones and growth problems for children. 

The FDA has recommended that doctors measure serum bicarbonate levels in the blood both before initiating Zonegran treatment and at intervals during the therapy even if there are no symptoms of the side effect.

If metabilic accidosis develops, the FDA indicates that the dose can be reduced or discontinued using dose tapering, and alkali treatment may be considered for patients with metabolic acidosis if zonisamide treatment is to be continued.