Background The vasopressin receptor 2 antagonist tolvaptan is an aquaretic agent that promotes water elimination to resolve hyponatraemia secondary to the syndrome of inappropriate antidiuretic hormone secretion (SIADH). There are ongoing studies researching its effectiveness in hyponatraemia secondary to heart failure, in which patients have body water excess that dilutes sodium.

Purpose To explore the efficacy of tolvaptan off-label use in hyponatraemia secondary to heart failure.

Material and methods Observational retrospective study carried out in a tertiary care hospital. We conducted a search to find all patients treated with tolvaptan. The next step was to identify off-label use in heart failure. Once patients were identified, we extracted their demographic data, laboratory tests and tolvaptan treatment duration and dosages. The data were inserted in an Excel chart to make a descriptive analysis.

Results 28 patients were found, but only 6 met off-label use criteria (2 women and 4 men). 1 patient passed away 72 h after his admission and was excluded. Median age was 70 years (range 54–80). Only 2 patients had a sodium charge with hypertonic saline fluid before tolvaptan treatment, but their sodium level did not increase. Neither had NaCl oral therapy. Mean tolvaptan dosage (calculated as total tolvaptan dosage in mg divided by treatment duration in days) was 15 ± 5 mg/day. Median treatment duration was 10 days (range 5–15). Mean natraemia levels were 120 ± 6 mEq/L at baseline, 124 ± 11 mEq/L after 24 h of treatment, 127 ± 5 mEq/L after 48 h of treatment and 130 ± 6 mEq/L after 72 h of treatment. The final mean natraemia level was 136 ± 3 mEq/L. The average sodium level increase was 16 ± 3 mEq/L. During tolvaptan treatment, 3 patients were receiving furosemide, 1 furosemide and hydrochlorothiazide, and 1 furosemide, chlorthalidone and spironolactone. These results are  consistent with those found by Salterain-Gonzalez et al (2013) and Rodríguez-de Muñoz et al (2013).

Conclusion Based on our data, it seems that tolvaptan is an effective option to increase natraemia in heart failure patients. However, due to our small population, we cannot conclude it categorically.

No conflict of interest.