A proportion of patients with fibrosing interstitial lung diseases (ILDs) 
develop a progressive phenotype characterised by decline in lung function, 
worsening quality of life and early mortality. Other than idiopathic pulmonary 
fibrosis (IPF), there are no approved drugs for fibrosing ILDs and a poor 
evidence base to support current treatments. Fibrosing ILDs with a progressive 
phenotype show commonalities in clinical behaviour and in the pathogenic 
mechanisms that drive disease worsening. Nintedanib is an intracellular 
inhibitor of tyrosine kinases that has been approved for treatment of IPF and 
has recently been shown to reduce the rate of lung function decline in patients 
with ILD associated with systemic sclerosis (SSc-ILD). In vitro data demonstrate 
that nintedanib inhibits several steps in the initiation and progression of lung 
fibrosis, including the release of pro-inflammatory and pro-fibrotic mediators, 
migration and differentiation of fibrocytes and fibroblasts, and deposition of 
extracellular matrix. Nintedanib also inhibits the proliferation of vascular 
cells. Studies in animal models with features of fibrosing ILDs such as IPF, 
SSc-ILD, rheumatoid arthritis-ILD, hypersensitivity pneumonitis and silicosis 
demonstrate that nintedanib has anti-fibrotic activity irrespective of the 
trigger for the lung pathology. This suggests that nintedanib inhibits 
fundamental processes in the pathogenesis of fibrosis. A trial of nintedanib in 
patients with progressive fibrosing ILDs other than IPF (INBUILD) will report 
results in 2019.