Nausea and
diarrhea are the most common adverse effects of
nintedanib in patients with
idiopathic pulmonary fibrosis (IPF). However, the clinical risk factors for these side effects remain unknown. In the present study, we investigated the characteristics of patients who developed gastrointestinal side effects during
nintedanib treatment for IPF and determined the risk factors for these side effects. We enrolled 77 patients with IPF who received
nintedanib between October 2015 and March 2018. Performance status (PS) as a patient's general condition, body mass index (BMI), modified Medical Research Council
Dyspnea Scale score, severity of IPF at
nintedanib initiation, and gastrointestinal toxicity of
nintedanib were evaluated. In total, 25 and 27 patients exhibited
nausea and
diarrhea, respectively, during the follow-up period. A poor PS, low BMI, and full dosage of
nintedanib at treatment initiation were risk factors for
nausea. A low BMI was a significant risk factor for
diarrhea, which could be prevented by combination treatment with
nintedanib and
prednisolone. In addition, the mean annual rate of decline in forced vital capacity was significantly greater in patients with
nausea than in patients without
nausea. In conclusion, our findings suggest that patients with a low BMI and/or poor PS and those who receive the full
nintedanib dosage at treatment initiation are more susceptible to gastrointestinal adverse effects during
nintedanib treatment. Addition of
prednisolone to the treatment regimen may prevent the development of
diarrhea during treatment.