Replacing rifampicin with minocycline increases the activity of the treatment regimen for Mycobacterium avium complex pulmonary disease in a dynamic hollow-fibre system.

Objective: Mycobacterium avium complex bacteria cause chronic pulmonary disease (MAC-PD) in susceptible patients. The recommended treatment regimen (rifampicin, ethambutol and azithromycin) achieves 65% cure rates but with considerable toxicity and drug-drug interactions [2,3]. Minocycline proved active in monotherapy experiments using the hollow-fibre model [4]. We compared the efficacy of the recommended regimen with a minocycline, ethambutol and azithromycin regimen using this model.

Methods: Epithelial lining fluid pharmacokinetic (PK) profiles of the recommended regimen and minocycline, ethambutol, azithromycin regimen were simulated. THP-1 cells infected with M. avium ATCC 700898 were exposed to these regimens for 21 d. PK profiles were determined at d 0 and d 21. The pharmacodynamic effect was measured by determining bacterial densities at d 0, 3, 7, 14 and 21 for intra- and extracellular fractions. Emergence of macrolide-resistance was monitored by inoculating azithromycin-containing agar, MIC measurements and resistance mutation analysis.

Results: The minocycline-containing regimen exhibited a 1.5 log10 CFU/mL lower bacterial burden than the recommended regimen at d 7, though both regimens lost effectiveness over time. Treatment failure in both arms was not linked to the emergence macrolide-resistance. PK profiles simulated in the model matched those in MAC-PD patients.

Conclusions: Replacing rifampicin with minocycline increased the antimycobacterial activity of the MAC-PD treatment regimen in the hollow-fibre model, without jeopardizing the prevention of macrolide-resistance. This promising minocycline-containing regimen is a candidate for inclusion in clinical trials.