Hyponatremia can be defined like the low sodium concentration, lower that 135 mmol/l. It becomes really serious when the concentration is lower than 120 mmol/l. The most frequent causes of hyponatremia are: the extrarenal loss (GIT, skin, bleeding, sequestration), the renal loss (diuretics, nephritis with the salt loss, osmotical diuresis, the Addison disease), hypothyroidism, the lack of glucocorticoids, emotional stress, pain, pseudohyponatremia (incorrect taking, dyslipoproteinemia). There is fatigue, exhaustion, headache and vertigoes dominating in the clinical record file. By the deficit increasing a patient becomes delirious, comatose even with the shock development. It is necessary to separate sufficient supply of sodium from much more often reason, which is loss of sodium which can be caused by: excessive sweating, vomitting with the metabolical alkalosis development, diarrhoea with the metabolical acidosis development, renal losses (a phase of renal failure). Treatment of hyponatremia: intensive treatment starts at the level of plasmatic concentration of sodium under 120 mmol/l or when neurological symptoms of brain oedema are present. In the therapy it is necessary to avoid fast infusions of hypertonic saline solutions (3-5% NaCl solutions) because of the danger of the development of serious CNS complications (intracranial bleeding, etc.). It is recommended to adjust the plasmatic concentration of sodium up to 120 mmol/l during the first four hours and a subsequent correction should not be higher than 2 mmol per an hour. Treatment of the basic illness is very important. We present 2 case histories: a 74-year old female patient and a 69-year old female patient both with the hyponatremia caused by taking of carbamazepine. We want to inform and warn about not only a well known side effect during long-term treatment but about hyponatremia that arose within 48 hours after the start of taking medicine as well.

1 Interná Klinika Lekárskej Fakulty UK a Martin Slovenská Republika Prednosta prof MUDr Marián Mokán DrSc FRCP Edin