Hyponatremia, an
electrolyte disturbance usually without clinical significance, may sometimes lead to serious complications when overlooked or not treated appropriately. One cause of
hyponatremia, the syndrome of inappropriate
antidiuretic hormone (
SIADH) secretion, has been associated with some drugs, including
carbamazepine (CBZ). Because of its
antidiuretic effects, CBZ has been used successfully to treat
diabetes insipidus centralis. Possible mechanisms for the
antidiuretic effects of CBZ have been proposed. Altered sensitivity to serum osmolality by the hypothalamic osmoreceptors appears likely, but an increased sensitivity of the renal tubules to circulating ADH cannot be excluded. CBZ has led to
hyponatremia in patients with
epilepsy,
neuralgia,
mental retardation, and
psychiatric disorders with a frequency varying from 4.8 to 40%.
Oxcarbazepine (OCBZ), which is structurally related to CBZ, has shown similar hyponatremic effects, but whether
hyponatremia occurs more often than with CBZ is not yet clear. Experience with OCBZ is still limited, and there is no definite explanation for a possible difference in antidiuretic potency. Most patients with CBZ/OCBZ-induced
hyponatremia are asymptomatic. In rare cases,
water intoxication has been reported, necessitating treatment discontinuation.