Mycobacterium abscessus causes chronic pulmonary
infections that are extremely difficult to cure. The currently recommended combination
therapy is associated with high failure rates and relapse.
Tigecycline has been explored in salvage regimens, with a response rate of 43% in those who received at least a month of
therapy. We performed a dose-response study in a hollow-fiber system model of pulmonary M. abscessus
infection in which we recapitulated
tigecycline human pulmonary concentration-time profiles of 8 different doses for 21 days. We identified the maximal kill or efficacy in CFU per milliliter and the ratio of the 0- to 24-h area under the concentration-time curve to MIC (AUC/MIC) associated with 80% efficacy (EC80). The
tigecycline efficacy was 5.38 ± 2.35 log10 CFU/ml, and the drug achieved the unprecedented feat of a bacterial level of 1.0 log10 CFU/ml below the pretreatment inoculum (1-log kill) of M. abscessus in the hollow-fiber system. The EC80 AUC/MIC ratio was 36.65, while that for a 1-log kill was 44.6. Monte Carlo experiments with 10,000 patients were used to identify the clinical dose best able to achieve the EC80 or 1-log kill. The standard dose of 100 mg/day had a cumulative fraction of response of 51% for the EC80 and 46% for 1-log kill. For both the EC80 target and 1-log kill, the optimal
tigecycline clinical dose was identified as 200 mg/day. The susceptibility breakpoint was ≤0.5 mg/liter.
Tigecycline is the most active single agent evaluated to date, and we propose that 200 mg/day be examined as the backbone of new combination
therapy regimens to replace current treatment.