Regimen comprising clarithromycin, clofazimine and bedaquiline is more efficacious than monotherapy in a mouse model of chronic Mycobacterium avium lung infection

Abstract

Mycobacterium avium, a leading non-tuberculous mycobacterium (NTM) pathogen, causes chronic pulmonary infections, particularly in individuals with underlying lung conditions or immunosuppression. Current treatments involve prolonged multi-drug regimens with poor outcomes and significant side effects, highlighting the urgent need for improved therapies. Using a BALB/c mouse model of chronic M. avium pulmonary disease, we evaluated the efficacy of individual antibiotics-clarithromycin, clofazimine, and rifabutin-and combination regimens including clarithromycin+bedaquiline and clarithromycin+clofazimine+bedaquiline. Clarithromycin demonstrated potent bactericidal activity, reducing lung bacterial burden by 2.2 log₁₀ CFU, while clofazimine transitioned from bacteriostatic to bactericidal, achieving a 1.7 log₁₀ CFU reduction. Rifabutin was bacteriostatic against M. avium MAC 101 but ineffective against MAC 104. The triple-drug regimen of clarithromycin+clofazimine+bedaquiline was the most effective, achieving a 3.3 log₁₀ CFU reduction in bacterial load, with 98% clearance within the first week and continued efficacy over eight weeks. Gross pathology confirmed these results, with granulomatous lesions observed only in untreated or rifabutin-treated mice. Combination therapy demonstrated enhanced efficacy compared to monotherapy. The findings underscore the potential of oral clarithromycin+clofazimine+bedaquiline or clarithromycin+clofazimine regimen as a promising therapeutic strategy for M. avium pulmonary disease.

Keywords: Mycobacterium avium; bedaquiline; clarithromycin; clofazimine; mouse model.

Figure 1:

M. avium MAC 101 (A) and MAC 104 (B) burden in the lungs of BALB/c mice. Time point week −4 represents 24 h after infection with respective strain via the aerosol route. Time point week 0 represents conclusion of four weeks of infection and the day of antibiotic treatment initiation. Time points week- 1, 4 and 8 represent the end of 1, 4 and 8 weeks of once daily oral administration of phosphate-buffered saline (PBS), 100 mg/kg clarithromycin (CLR), 25 mg/kg clofazimine (CFZ), and 20 mg/kg rifabutin (RFB). Mean CFU per lung and standard deviation are shown (n=5 per time point per group). (C) Gross pathology of the lungs of mice infected with MAC 104 from each treatment group, two mice per group at the conclusion of treatment (week 8) are shown.

Figure 2:

(A) M. avium MAC 101 burden in the lungs of BALB/c mice. Time point week −4 represents 24 h after infection via the aerosol route. Time point week 0 represents conclusion of four weeks of infection and the day of antibiotic treatment initiation. Time points week- 1, 4 and 8 represent the end of 1, 4 and 8 weeks of once daily oral administration of phosphate-buffered saline (No treatment), 100 mg/kg clarithromycin (CLR), 25 mg/kg bedaquiline (BDQ) and 25 mg/kg clofazimine (CFZ). Mean CFU per lung and standard deviation are shown (n=5 per time point per group). (B) Percentage reductions in the mean MAC 101 burden in the lungs of mice treated with 100 mg/kg clarithromycin + 25 mg/kg clofazimine + 25 mg/kg bedaquiline during the first week, second-fourth week, and fifth-eighth week are shown. (C) Gross pathology of the lungs of mice infected with MAC 101 from each treatment group, two mice per group, at the conclusion of treatment (week 8) are shown.