Objective To analyse the efficacy and safety of using tolvaptan and the suitability of its prescription with the criteria set forth in the pharmacotherapeutic guide of a tertiary hospital.

Method A retrospective, observational study on tolvaptan prescriptions issued in the hospital since its inclusion in the pharmacotherapeutic guide in October 2010, until February 2013. Data were collected from the patient’s electronic medical records and the computer-assisted prescription programme.

Results A total of 80 patients (52.3% males) with an average age of 68.8 (SD=14.6) years were included. The most common diagnosis for its prescription was heart failure (52.3% of cases). The initial mean for plasma sodium levels was 125.5 (SD=7.2) mEq/L. Tolvaptan use increased sodium levels to 135 mEq/L in 59.3% of patients. The median duration of treatment was 4 days (range 1–53 days). No significant differences were observed in other laboratory parameters tested. The average cost per patient was €487.80. Tolvaptan prescriptions were issued in accordance with the hospital’s pharmacotherapeutic guide in 66.6% of the cases.

Conclusions Treatment with tolvaptan safely and effectively increases plasma sodium levels in patients with hyponatraemia originating for various reasons, despite its approval for use by the EMA solely for cases of hyponatraemia secondary to syndrome of inappropriate antidiuretic hormone secretion.