Topiramate and metabolic acidosis: an evolving story

Topiramate is an anticonvulsant that is being increasingly used for a number of different off-label indications. Its inhibition of carbonic anhydrase isoenzymes can lead to metabolic acidosis, elevated urine pH, reduced urine citrate, and hypercalciuria, thereby creating a milieu that is ripe for calcium phosphate stone formation. In this review, we describe a case of topiramate-induced metabolic acidosis. We review the frequency of metabolic acidosis among children and adults, as well as the mechanism of hyperchloremic metabolic acidosis and renal tubular acidosis in topiramate users. Finally, we describe the long-term effects of topiramate-induced metabolic acidosis, including nephrolithiasis, nephrocalcinosis, and bone degradation. Patients who are prescribed topiramate should be carefully monitored for metabolic derangements, and they may benefit from alkali supplementation, or in extreme cases, discontinuation of the drug altogether.