Serum sodium levels and related treatment-emergent adverse events during eslicarbazepine acetate use in adults with epilepsy

Objective: To examine the frequency of hyponatremia and potentially related symptoms in clinical trials of eslicarbazepine acetate (ESL) in adults with focal- (partial-) onset seizures.

Methods: This post hoc, exploratory analysis included data from three controlled phase 3 trials of adjunctive ESL (400-1200 mg once daily), two phase 3 trials of ESL monotherapy (1200-1600 mg once daily), and their open-label extension studies. Exploratory endpoints included clinical laboratory measurements of serum sodium concentrations ([Na⁺ ]), incidences of hyponatremia-related treatment-emergent adverse events (TEAEs), and incidences of TEAEs that are potential symptoms of hyponatremia.

Results: The controlled trials of adjunctive ESL and ESL monotherapy included 1447 (placebo, n = 426; ESL, n = 1021) and 365 (ESL, n = 365) patients, respectively; 639 and 274 patients continued onto uncontrolled, open-label extensions. In the controlled and uncontrolled trials ≤3.3% of patients taking ESL had a minimum postdose [Na⁺ ] measurement ≤125 mEq/L, <9% had a >10 mEq/L decrease in [Na⁺ ] from baseline, <6% had a hyponatremia-related TEAE, and <2% discontinued the controlled trials due to a hyponatremia-related TEAE. Hyponatremia appeared to be more frequent in the monotherapy (vs adjunctive therapy) trials; in the controlled trials of adjunctive ESL and ESL monotherapy, incidence generally increased with increasing ESL dose. The majority of patients with an investigator-reported TEAE of "hyponatremia" or "blood sodium decreased" did not have a corresponding laboratory [Na⁺ ] measurement ≤125 mEq/L. Some symptoms potentially related to hyponatremia (including nausea and vomiting) were more frequent in patients with a minimum postdose [Na⁺ ] measurement ≤125 mEq/L.

Significance: Reductions in serum sodium concentrations and hyponatremia-related TEAEs occurred in a small number of patients taking ESL. Suspected hyponatremia should be confirmed and monitored via [Na⁺ ] measurements.