Abstract
Background: Hyponatremia is a common electrolyte abnormality encountered in hospital wards. Even mild hyponatremia can result in significant morbidity and mortality especially in elderly. Treatment of the condition depends on the volume status of the patient, duration and severity of hyponatremia, and clinical condition of the patient.

Aims and Objectives: Tolvaptan is an oral vasopressin receptor antagonist approved for use in euvolemic and hypervolemic hyponatremia. The present study aimed to assess the effectiveness and safety of tolvaptan 15 mg daily for 3 days in patients with euvolemic and hypervolemic hyponatremia.

Materials and Methods: This study was a prospective observational study conducted on 82 patients with euvolemic and hypervolemic hyponatremia in whom tolvaptan was given in the Department of General Medicine in a tertiary care teaching hospital in south India. History, clinical examination findings, and baseline laboratory values were recorded in the structured proforma. Serum sodium levels were done daily along with other laboratory parameters such as renal function test, serum electrolytes, liver function tests, and random blood sugar. The rise in serum sodium level and the occurrence of overcorrection was noted. Adverse effects developing during treatment were recorded.

Results: By day 3, 27% of patients achieved normonatremia and hence tolvaptan was stopped after 2 doses. By day 4, 84% of patients who took tolvaptan achieved normonatremia. Overly rapid correction of hyponatremia was observed in 9.8% of patients. There was a significant correlation between day 1 sodium and day 4 sodium as well as day 1 sodium and total correction. The mean increase in serum sodium with 3 doses of tolvaptan was 18.24 mEq/L with a P < 0.0001. The adverse events during the study period were mild and included increased thirst, dry mouth, and polyuria. There was no significant change in transaminase levels during treatment.

Conclusion: Tolvaptan is highly effective in increasing serum sodium level in hyponatremia with minimal adverse effects. The risk of an overly rapid correction is present with its use and is more in severe hyponatremia. This can be minimized by frequent monitoring of sodium level and ensuring adequate fluid intake.

Key words: Tolvaptan; Hyponatremia; Osmotic Demyelination Syndrome; Overcorrection