Renal tubular acidosis associated with zonisamide therapy

Purpose: We sought to report a previously undescribed adverse effect, renal tubular acidosis associated with zonisamide (ZNS) therapy. Methods: Ammonium chloride, bicarbonate, and furosemide loading tests were performed in an epileptic patient with metabolic acidosis and episodic hypokalemia who was treated with ZNS. Results: Distal renal tubular acidosis was diagnosed. On reexamination 7 weeks after ZNS had been replaced with phenytoin, the renal tubular acidosis disappeared. Conclusions: This case indicates, for the first time, that ZNS might be a potential cause of renal tubular acidosis. Blood gases and serum electrolytes should be measured in patients undergoing ZNS therapy.