Hyponatremia during carbamazepine therapy.

Sixty patients receiving carbamazepine and 61 age-matched controls were studied to determine the prevalence of hyponatremia. There was a significant difference between the mean (+/- SE) serum sodium levels of the subjects (138.8 +/- 0.6 mEq/L) and the controls (141.7 +/- 0.4 mEq/L). Thirteen (21.7%) of the subjects, but none of the controls, had sodium levels less than 135 mEq/L. The risk of hyponatremia increased with age (subjects greater than 30 years old had four times the prevalence of hyponatremia as those less than 30 years old) and carbamazepine serum level (those with levels greater than 6 micrograms/ml had three-and-a-half times the prevalence as those with lower levels).