The regulation of serum sodium after replacing carbamazepine with oxcarbazepine

Purpose: To evaluate changes in serum electrolyte balance and underlying re gulatory mechanisms in 10 male patients with epilepsy 2 and 6 months after replacing long-term carbamazepine (CBZ) monotherapy with oxcarbazepine (OCB Z) monotherapy. Arginine vasopressin (AVP) is thought to be most important underlying mechanism of CBZ-related hyponatremia via direct or kidney tubul ar mechanisms. Furthermore, AVP is as well hormonally regulated by the reni n-angiotensin-aldosterone system and atrial natriuretic peptide (ANP). Methods. The medication of the patients was changed from CBZ to OCBZ. Serum electrolytes, creatinine, albumin, aldosterone, and the N-terminal fragmen t of ANP (NT-proANP) concentrations were measured before and 2 and 6 months after the change in the medication. Results: The mean serum sodium level diminished after the medication was ch anged. Serum sodium levels decreased below the reference range in two (20%) patients during OCBZ medication. Serum sodium levels decreased altogether in four patients. and remained unaltered in six patients. Serum aldosterone levels increased in the six patients whose serum sodium concentrations did not decrease, but no increase was found in the patients with decreased sod ium levels during OCBZ medication. Serum NT-proANP levels decreased in all patients. Conclusions: Serum sodium levels decrease after replacing CBZ with OCBZ. Th e low serum NT-proANP concentrations appear to reflect the decreased serum sodium levels, but a compensatory aldosterone response may prevent the deve lop ment of hyponatremia in some patients during OCBZ medication.