Association between topiramate use and serum bicarbonate levels in a veteran population.

BACKGROUND Topiramate has been associated with metabolic acidosis secondary to decreased serum bicarbonate. Product labeling recommends serum bicarbonate monitoring at baseline and periodically thereafter. OBJECTIVE The study objective was to assess changes in serum bicarbonate within the first year of topiramate use in an outpatient veteran population. METHODS This was a single-center, retrospective study conducted at the Iowa City Veterans Affairs Health Care System. Inclusion criteria required a minimum of 1 topiramate outpatient prescription between October 1, 1999, and August 31, 2012, and at least 1 serum bicarbonate level within 12 months prior to topiramate initiation. Patients with topiramate nonadherence, concurrent use of sodium bicarbonate or oral carbonic anhydrase inhibitors, and individual serum bicarbonate values obtained during inpatient hospitalizations were excluded. Change in bicarbonate was evaluated using a paired t test. Decreases in bicarbonate of ≥5 mEq/L, values <20 mEq/L, days to lowest value, and correlation between adverse drug reactions (ADRs) and topiramate discontinuation were evaluated. RESULTS Of 546 patients reviewed, 350 were included in the analysis. There was a statistically significant decrease of 2.7 mEq/L in bicarbonate following initiation of topiramate. Only 1 patient had a bicarbonate value <17 mEq/L. There was no association between bicarbonate decrease ≥5 mEq/L and ADRs. CONCLUSIONS A statistically significant reduction in bicarbonate levels occurred with topiramate, which was clinically insignificant. ADR occurrence did not correlate with bicarbonate levels <17 mEq/L or a decrease ≥5 mEq/L. Our results indicate that serum bicarbonate levels should only be monitored before topiramate initiation and in patients presenting with symptoms suggestive of acidosis.