Carbamazepine and serum sodium levels

Serum sodium levels of 674 epileptic patients were tabulated according to the following categories: less than 135 mmol/L, hyponatremia (28 patients); 135-145 mmol/L, normonatremia (530 patients); greater than 145 mmol/L, hypernatremia (116 patients). One hundred one patients were treated with antiepileptics without carbamazepine (CBZ), 113 with CBZ monotherapy, and 460 with CBZ plus other antiepileptic drugs. Twenty-three patients could be followed up after the first detection of a serum sodium level of less than 135 mg/L. Ten patients were consistently hyponatremic (greater than 50% of the follow-up measurements were less than 135 mg/L), whereas the remaining 13 were occasionally hyponatremic. The following facts could be derived from the study: (1) The hyponatremic group was significantly older compared with the other groups. (2) In patients not treated with CBZ, no hyponatremia was seen. Only two patients on CBZ monotherapy showed hyponatremia. (3) The combination of CBZ, valproic acid, especially in high dosages, and barbiturates seemed to lead to hyponatremia. (4) The excretion of antidiuretic hormone, measured in 12 patients, was subnormal (less than 25 ng/24 h) in seven hyponatremic patients and in three normonatremic patients and normal (25-250 ng/24 h) in two other normonatremic patients. (5) Cyclic AMP, measured in five hyponatremic patients, was normal. (6) In all patients the hyponatremia was slight and did not cause any clinical symptoms. Special treatment was not required.