Hyponatremia associated with carbamazepine and oxcarbazepine therapy: a review

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.

Effects of antiepileptic drugs on hormones

A hormone is an intrinsic substance carried via the blood to a target organ which is then functionally stimulated. Similar to extrinsically administered medications, the metabolism and function of the hormones may be altered by antiepileptic drugs (AEDs). The proposed mechanisms are (a) enhanced metabolism (natural steroids, synthetic steroids, e.g., decadron and birth control pills, thyroxine, and vitamin D3), (b) altered protein bonding (thyroxine, sex hormones), (c) impaired release into the systemic circulation (calcitonin, insulin, vitamin K clotting factors) and (d) altered end-organ effect. The AEDs most likely to interact with hormones are barbiturates, carbamazepine, and phenytoin.

Alcohol withdrawal and carbamazepine

The use of pharmacologic intervention in the management of alcohol withdrawal syndrome is briefly presented. The use of carbamazepine, a tricyclic anticonvulsant with clinical efficacy in depressive illness, in alcohol withdrawal treatment is reviewed. A comparative analysis between carbamazepine and major drugs used in alcohol withdrawal syndrome is made. This includes the evaluation of both clinical advantages and disadvantages in addition to identification of drug adverse reaction and interaction with alcohol. The mechanism of action of carbamazepine is also examined. Carbamazepine appears to possess a useful pharmacotherapeutic potential in the management of acute alcohol withdrawal syndrome, and its use in long-term treatment is suggested.

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.