The present study demonstrated that treatment with antifibrotic agents was independent factor for better survivals in IPF patients who were introduced LTOT in a real-life study. To our knowledge, this is the first study evaluating the significance of antifibrotic medication on the prognosis of IPF patients with LTOT.
The prognosis of IPF is poor and the mean survival time from diagnosis is 3–5 years (1, 2). Several parameters to predict mortality of patients with IPF have been reported. Age, gender, percent predicted VC, percent predicted FVC and percent predicted DLco, which were also component of modified GAP scores, have been generally accepted as prognostic factors in IPF (9, 13). In addition, BMI and systemic inflammatory indices such as NLR, ALI, GPS were reported to be prognostic markers in chronic lung diseases including IPF (7, 8, 14–16). We investigated those possible factors for survival of IPF after initiation of LTOT, however, only gender female and treatment with antifibrotic agents were favorable factors.
Chronic hypoxemia is a common feature during clinical course of IPF and supplemental oxygen is strongly recommended for patients with advanced IPF in order to reduce breathlessness and improve exercise tolerance (2, 4, 5, 17). Even though its frequent use of LTOT, there is little information regarding the effectiveness of oxygen therapy and prognosis after initiation of LTOT in interstitial lung disease (ILD) including IPF. A systematic review showed that the use of LTOT in ILD was at high risk of bias and impossible to estimate impacts on survival (3).
Higashiguchi et al. reported the 2-year survival rate of 49 idiopathic interstitial pneumonia (IIP) patients was 36.0%. Male gender and lower BMI were independent predictive prognostic factor of IIP patients with LTOT (18). Ahmadi et al. showed that the survival from initiation of LTOT was median 8.4 months in 285 ILD patients (19). Rantala et al. recently reported that the median survival of ILD patients with LTOT was 10.8 months, and the 1-yr survival was 47% in 138 ILD subjects (20). In this study limited to the IPF patients, the median survival of all subjects from initiation of LTOT is 11.7 months similar to previous studies. However, the median survival of IPF patients treated with antifibrotic agents was significantly longer than that of patients without antifibrotics (20.4 vs. 7.9 months, p = 0.0165). The comparison of the patient groups stratified by the use of antifibrotic agents showed no significant difference in the characteristics and disease severity such as age, BMI, modified GAP score and GPS. The results from multivariable analysis and comparison of survival curve suggest that treatment with antifibrotic agents may be beneficial in IPF patients even after initiation of LTOT.
Australian and European IPF registry studies showed that patients receiving antifibrotic medications had better survival those not on antifibrotic medications (21, 22). The favorable effect of antifibrotic agents on better survival has been reported not only in clinical trial but also in real-world setting. In addition, preliminary data suggested the efficacy of both antifibrotic agents in severe IPF with lung function impairment (FVC < 50%). (23). In the present study, most of IPF patients were treated with doses of both nintedanib (200mg/day) and pirfenidone (600-1200mg/day) due to tolerability issues. Recent retrospective study demonstrated beneficial effects of low-dose pirfenidone (600-1200mg/day) on survival and pulmonary function decline in IPF patients (24). The choice, initiation timing and dose reduction of antifibrotic agents could be associated with physicians’ experience, patients’ severity and possible adverse events in a real-world setting. Continuation of antifibrotic agents with low-dose may be beneficial for IPF patients even after initiation of LTOT. Prognostic efficacy of antifibrotic medication on survival in IPF with LTOT will be further investigated in the future, using large number of subjects.
The limitations of the study are its retrospective nature and potential selection bias. First, we were not able to study all the possible factors that influenced the survival of IPF patients with LTOT. Due to progressive dyspnea and insufficient forced lung volume of the subject, modified GAP scores were not obtained from all IPF patients. Second, as described, the criteria of dose- reduction or discontinuation of antifibrotic agents were not yet standardized and, thus, decided by the attending doctors.
In conclusion, from a real-world clinical setting, gender female and treatment with antifibrotic agents were both clinical predictors for IPF patients after initiation of LTOT. On multivariable analysis, treatment with antifibrotic agents was the independent factor of favorable survival of IPF patients with LTOT. This finding could provide better prognosis in IPF patients even after the initiation of LTOT.