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
