Summary

Pirfenidone was approved in October 2014 in the USA for the treatment of idiopathic pulmonary fibrosis. Although not included in the adverse events published in the CAPACITY-1 and CAPACITY-2 or ASCEND trials, hyponatraemia was reported in supplementary data with rate of 3.4% in the active therapy arm versus 0.3% in the placebo arm. We performed a retrospective analysis of patients who were initiated on pirfenidone or nintedanib for the treatment of pulmonary fibrosis at our centre. Of the 52 patients who were started on pirfenidone, three (5.8%) developed severe hyponatraemia. Of the 29 patients who were started on nintedanib, none developed hyponatraemia. Laboratory data suggested syndrome of inappropriate antidiuretic hormone secretion (SIADH) induced by pirfenidone and the medication was discontinued. Hyponatraemia is a possible significant adverse effect of pirfenidone, able to induce SIADH in patients taking the medication.