Use of vaptans in treatment of hyponatremia
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Hyponatremia is the most prevalent electrolyte imbalance, and may be present in up to 30% of hospitalized patients. It is an important predictor of in-hospital mortality. Irrespective of the reason underlying hyponatremia, water metabolism plays an important role. Arginine-vasopressin, which has cardiovascular effects and plays a role in water metabolism, is released from the posterior hypothalamus in response to an increase in plasma osmolality or a drop in the blood pressure, which are detected by osmoreceptors and baroreceptors respectively. Arginine-vasopressin has receptors located on vascular smooth muscle cells, the heart (V1a), the collecting ducts of the renal medulla (V2), the anterior pituitary gland (V1b) and many other organs. Arginine-vasopressin antagonists, known as “vaptans”, have recently attracted attention for the treatment of chronic hypotonic hyponatremia. In this review, we focus on the diagnosis and classification of hyponatremia, current trends in its treatment in the light of guidelines, and the rationale of using vaptans in treating hyponatremia. We also briefly review cornerstone studies in the literature regarding vaptans, and the correct indications, contraindications and cautions in the use of “tolvaptan” and “conivaptan”, two approved vaptans for this indication.