An RCT of Mycophenolate Mofetil (MMF) in Fibrotic Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is a complex immunologically‐mediated interstitial lung disease (ILD) resulting from sensitization to an inhaled antigen. It may be categorized into acute (acute/subacute) or chronic forms based on the duration of disease or evidence of chronicity on radiological or pathological findings. Lately, the American Thoracic Society (ATS) Guidelines 2020 has endorsed a new classification of HP into non‐fibrotic and fibrotic types based on the absence or presence of signs of fibrosis on chest computed tomography (CT) or histology. According to a survey study, about three‐fourths of respiratory physicians believe that fibrotic HP should be treated with glucocorticoids as the treatment of first choice, which also reflects the practice in most centers worldwide. However, there is some evidence that glucocorticoids may not be effective in the long‐term treatment of fibrotic HP. Also, glucocorticoids are associated with several adverse effects especially when used over a long duration. Therefore, most experts recommend that glucocorticoids should be tapered to the lowest possible dose after a trial of about three months in chronic/fibrotic HP. Hypersensitivity pneumonitis is characterized by an exaggerated T cell‐mediated immune inflammatory response (T‐lymphocytic alveolitis) due to increased migration, local proliferation, and decreased programmed cell death of lymphocytes. Mycophenolate mofetil (MMF) is an immunosuppressive drug that acts by inhibiting the proliferation of T‐lymphocytes and suppressing the recruitment of lymphocytes and monocytes into the sites of inflammation. Therefore, MMF is likely to be effective in the treatment of HP. There are only a few retrospective studies on the efficacy of MMF in the treatment of HP. To our knowledge, there is no randomized controlled trial assessing the efficacy of MMF in the treatment of HP. We aim to perform a randomized study to assess the efficacy and safety of a regimen consisting of MMF and prednisolone against a regimen consisting of prednisolone alone for treating fibrotic HP. We hypothesize that the treatment of patients with fibrotic HP with MMF and prednisolone will be more effective and safer than treatment with prednisolone alone.