The Kinetics of Bedaquiline Diffusion in Tuberculous Cavities Open a Window for the Emergence of Resistance.

Background: Cavitary tuberculosis is difficult to cure and constitutes a site of relapse. Bedaquiline has been a wonder drug in the treatment of multidrug-resistant tuberculosis, but emergence of resistance threatens the sustainability of its success. We designed site-of-disease pharmacokinetic studies to spatially resolve the penetration of bedaquiline, and 2 next-generation diarylquinolines, TBAJ876 and TBAJ587, in cavities.

Methods: Rabbits with established cavitary tuberculosis received the study drugs. A laser-capture microdissections scheme was developed to measure drug concentrations as a function of distance from blood supply in caseum. To simulate drug coverage in patient cavities, the data were modeled, and parameter estimates were linked to clinical plasma pharmacokinetic models.

Results: Pharmacokinetic-pharmacodynamic simulations in caseum revealed that bedaquiline reaches steady state and efficacious concentrations in deep caseum after several weeks to months and lingers at subtherapeutic concentrations up to 3 years after therapy ends. TBAJ876 and TBAJ587, achieve bactericidal concentrations in caseum layers more rapidly and shorten the window of suboptimal concentrations post treatment compared to bedaquiline.

Conclusions: The slow kinetics of diffusion of bedaquiline into and out of caseum creates spatiotemporal windows of subtherapeutic concentrations. Site-of-disease simulations of TBAJ587 and TBAJ876 predict reduced opportunities for resistance development.