Impact of Topiramate on Serum Bicarbonate Concentrations in Adults

BACKGROUND: Topiramate is an antiepileptic medication with multiple pharmacologic effects, including inhibition of carbonic anhydrase activity. It is associated with metabolic acidosis in both children and adults. OBJECTIVE: To evaluate the incidence and magnitude of the effect of topiramate on serum bicarbonate concentrations in an adult population. METHODS: This was a retrospective cohort study. Data were evaluated to assess the relationship between serum bicarbonate concentrations before and during topiramate therapy. RESULTS: Fifty-four patients (40 females) with a mean age of 47.6 years (range 19–89) were included in the study. Mean ± SD serum bicarbonate concentrations before and during topiramate therapy were 26.8 ± 2.9 mEq/L (range 21–36) and 21.7 ± 3.6 mEq/L (range 13–29), respectively, with a mean difference of 5.1 (95% CI 3.7 to 6.5; p < 0.001). Twenty-six patients (48%) had low serum bicarbonate concentrations while on topiramate, with a mean concentration of 18.8 mEq/L (range 13–21). CONCLUSIONS: Topiramate was associated with metabolic acidosis in 48% of the patients studied, which did not result in clinically significant problems.