In this meta-analysis, we reviewed four RCTs[12, 18, 20, 21] which compared the use of additional antimicrobial agents with placebo or usual care in terms of efficacy and safety for the treatment of adult patients with IPF. Our findings showed that antimicrobial agents (co-trimoxazole or doxycycline) did not provide additional benefits for patients with IPF in terms of mortality and FVC. In contrast, these agents were significantly associated with a higher risk of AEs, especially gastrointestinal toxicity. Based on these findings, the additional use of antimicrobial therapy for patients with IPF is not recommended.
Anti-fibrotic agents including pirfenidone and nintedanib have been approved and are widely used in several countries for the treatment of IPF. However, these two agents may not be available or affordable in certain countries. Immunomodulatory agents including azathioprine, colchicine, cyclophosphamide and interferon-gamma 1b have been investigated for the treatment of IPF, however, they have failed to show treatment benefits.[24] In addition, a recent meta-analysis also indicated that add-on anti-oxidative therapy with N-acetylcysteine to pirfenidone did not affect outcomes compared to pirfenidone alone.[25]
An earlier in vitro study showed that doxycycline could attenuate pulmonary fibrosis through the inhibition of growth factor and MMP production in alveolar epithelial cells.[13] Using a murine model, Kalemci et al demonstrated that the administration of minocycline may be effective in methotrexate-induced lung fibrosis.[14] In patients with IPF, Mishra et al showed that doxycycline therapy reduced the levels of MMP-9, MMP-3, tissue inhibitor of metalloproteinase-1 and vascular endothelial growth factor in bronchial alveolar lavage fluid to near control values.[16] Previous studies have also demonstrated that the lung microbiome and bacterial burden can influence disease progression and outcomes in patients with IPF.[26, 27]
However, in the current meta-analysis, we found that the additional use of antimicrobial agents did not provide clinical benefits in patients with IPF. The reason for our negative findings could be multifactorial. First, our findings were based on the analysis of intention-to-treat populations, not per-protocol populations, and adherence to the study medications was poor in the included RCTs. In Shulgina’s trial,[18] the adherence rate to the study medication (co-trimoxazole) was only 66.3% (63/95). In the EME-TIPAC trial of 169 patients randomized to receive co-trimoxazole,[20] 67 (39.6%) patients discontinued the medication and 26 (15.4%) reduced the dose. In the CleanUP-IPF trial,[21] adherence to the study medication at 12 months was only 47.2% among 163 patients, and only 49.5% of the study patients were followed up for more than 12 months. In addition, the findings of per-protocol analysis in Shulgina’s study showed that co-trimoxazole was associated with a significant reduction in all-cause mortality (hazard ratio, 0.21; 95% CI, 0.06 to 0.78; p = 0.02) even though co-trimoxazole did not show a survival benefit based on the analysis of the intention-to-treat populations.[18] Therefore, these findings raise the question of whether the insignificant effect of additional antimicrobial therapy could be due to poor adherence, and further studies with better adherence are warranted to solve this issue. Second, there was heterogeneity among the included RCTs, including the characteristics of each study population. The diagnostic criteria of IPF, severity of baseline lung function, underlying comorbidities, and treatment duration varied among these studies. Furthermore, anti-fibrotic agents were not available in two earlier studies,[12, 18] and more than 70% of the IPF patients received anti-fibrotic agents in the two most recent studies.[20, 21] Whether anti-fibrotic agents can influence the effect of anti-microbial agents is unknown. In addition, none of the included studies measured the number or type of lung microbes or the direct effect of antimicrobial agents on these microbiota, and therefore we cannot exclude the potential effect of antibiotics in selected patients with IPF and dysbiosis.
In terms of safety analysis, we found that the use of additional antimicrobial agents was significantly associated with a higher risk of AEs, especially gastrointestinal toxicity including diarrhea and vomiting, and a trend of dermatological side effects such as skin rash. These AEs were expected to be higher in the experimental group, however most were not fatal or serious. For other AEs, there were increased risks of hematological and renal disorders such as hyperkalemia and impaired renal function, although these differences did not reach statistical significance. However, the included patients in the trials were highly selected, and additional side effects associated with antimicrobial agents still need to be cautiously monitored in a clinical setting.
This meta-analysis had several limitations. First, the numbers of included studies and patients were relatively small, and adherence to the study medication was poor as mentioned above. Second, the antimicrobial agents were limited to co-trimoxazole or doxycycline, and the potential anti-bacterial benefits of co-trimoxazole may have been reduced due to widespread bacterial resistance. Other antibiotics such as macrolides and fluoroquinolones were not investigated in large studies. Third, we did not assess the effect of additional antimicrobial agents on other outcomes such as exercise tolerance with the six-minute walk test, risk of exacerbations or hospitalization, and quality of life because of a lack of data or differences in the measuring tools in different studies. However, the primary outcome in this meta-analysis demonstrated no significant difference in mortality in the patients who received additional antimicrobial agents, and this finding remained unchanged in leave-one-out sensitivity analysis, which could strengthen the results of this meta-analysis.