Risk factors of oxcarbazepine-induced hyponatremia in patients with epilepsy

Objectives: To determine the risk factors for hyponatremia in patients with epilepsy treated with oxcarbazepine (OXC). Methods: Seventy-three adult patients with epilepsy aged older than 17 years who received OXC therapy were enrolled in this study. Patients who had hyponatremia due to any etiology before OXC therapy and patients receiving OXC therapy for nonepileptic disorders were excluded from this study. The baseline level of serum sodium of the patients was measured before the OXC therapy. During OXC therapy, serum sodium levels were measured at least once per 3 months. Results: The frequency of hyponatremia (Na, ≤134 mEq/L) was 24.7% (n = 18) in patients with OXC therapy, and 8.2% (n = 6) of the patients had severe hyponatremia (Na, ≤128 mEq/L). The degree of decline in serum sodium concentration was significantly negatively correlated with the dosage of OXC. An increase of 1 mg in the dosage of OXC increased the risk of hyponatremia by 0.2%. Moreover, increasing the number of combination antiepileptic drugs increased the risk of hyponatremia. Conclusions: Higher dosages of OXC and the number of combination antiepileptic drugs may increase the risk of OXC-induced hyponatremia in patients with epilepsy. Most patients are asymptomatic, but if symptoms of hyponatremia, such as headache, general malaise, gait disturbance, and somnolence, are suspected, the serum sodium level should be measured; it may be necessary to decrease the OXC dose or to discontinue the drug.