These data, based on a preclinical model, demonstrate that nonadherence alone is not a sufficient condition for MDR-tuberculosis emergence.

Pharmacokinetic variability to a single drug in the regimen is significantly associated with failure of therapy and ADR in patients. This suggests that individualized dosing for tuberculosis may be more effective than standardized dosing, which is prescribed in directly observed therapy programs.

ABSTRACTWe hypothesize that low-level efflux pump expression is the first step in the development of high-level drug resistance in mycobacteria. We performed 28-day azithromycin dose-effect and dose-scheduling studies in our hollow-fiber model of disseminatedMycobacterium avium-M. intracellularecomplex. Both microbial kill and resistance emergence were most closely linked to the within-macrophage area under the concentration-time curve (AUC)/MIC ratio. Quantitative PCR revealed that subtherapeutic azithromycin exposures over 3 days led to a 56-fold increase in expression of MAV_3306, which encodes a putative ABC transporter, and MAV_1406, which encodes a putative major facilitator superfamily pump, inM. avium. By day 7, a subpopulation ofM. aviumwith low-level resistance was encountered and exhibited the classic inverted U curve versus AUC/MIC ratios. The resistance was abolished by an efflux pump inhibitor. While the maximal microbial kill started to decrease after day 7, a population with high-level azithromycin resistance appeared at day 28. This resistance could not be reversed by efflux pump inhibitors. Orthologs of pumps encoded by MAV_3306 and MAV_1406 were identified inMycobacterium tuberculosis,Mycobacterium leprae,Mycobacterium marinum,Mycobacterium abscessus, andMycobacterium ulcerans. All had highly conserved protein secondary structures. We propose that induction of several efflux pumps is the first step in a general pathway to drug resistance that eventually leads to high-level chromosomal-mutation-related resistance in mycobacteria as ordered events in an “antibiotic resistance arrow of time.”

These data inform interventional strategies relevant to drug delivery, dosing, and diagnostics to prevent the development of acquired resistance. The role of high intracavitary penetration as a biomarker of antibiotic efficacy, when assessing new regimens, requires clarification.

Background. The role of drug concentrations in clinical outcomes in children with tuberculosis is unclear. Target concentrations for dose optimization are unknown.Methods. Plasma drug concentrations measured in Indian children with tuberculosis were modeled using compartmental pharmacokinetic analyses. The children were followed until end of therapy to ascertain therapy failure or death. An ensemble of artificial intelligence algorithms, including random forests, was used to identify predictors of clinical outcome from among 30 clinical, laboratory, and pharmacokinetic variables.Results. Among the 143 children with known outcomes, there was high between-child variability of isoniazid, rifampin, and pyrazinamide concentrations: 110 (77%) completed therapy, 24 (17%) failed therapy, and 9 (6%) died. The main predictors of therapy failure or death were a pyrazinamide peak concentration <38.10 mg/L and rifampin peak concentration <3.01 mg/L. The relative risk of these poor outcomes below these peak concentration thresholds was 3.64 (95% confidence interval [CI], 2.28–5.83). Isoniazid had concentration-dependent antagonism with rifampin and pyrazinamide, with an adjusted odds ratio for therapy failure of 3.00 (95% CI, 2.08–4.33) in antagonism concentration range. In regard to death alone as an outcome, the same drug concentrations, plus z scores (indicators of malnutrition), and age <3 years, were highly ranked predictors. In children <3 years old, isoniazid 0- to 24-hour area under the concentration-time curve <11.95 mg/L × hour and/or rifampin peak <3.10 mg/L were the best predictors of therapy failure, with relative risk of 3.43 (95% CI, .99–11.82).Conclusions. We have identified new antibiotic target concentrations, which are potential biomarkers associated with treatment failure and death in children with tuberculosis.

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Background In the treatment of tuberculosis, ethambutol is used in case there is isoniazid resistance. We examined for the emergence of drug resistance to ethambutol monotherapy in pharmacokinetic-pharmacodynamic studies in the hollow fiber system. Methods Dose–effect studies and dose-scheduling studies were carried out with ethambutol and log-phase growth Mycobacterium tuberculosis to identify exposures and schedules linked to optimal kill and resistance suppression. In one study, after 7 days of ethambutol 300 mg/day isoniazid was administered to each system to determine its early bactericidal activity (EBA). Results Efflux-pump blockage reduced the mutation frequency to ethambutol 64-fold. In dose-effect studies, ethambutol had a maximal EBA of 0.22 log10 CFU/ml/day, as encountered in patients. By day 7, resistance had arisen to both ethambutol and isoniazid. Prior exposure to ethambutol abolished isoniazid EBA. Daily therapy, as opposed to more intermittent therapy, was associated with the least proportion of efflux-pump driven resistance, consistent with time driven effect. Microbial kill was best explained by the ratio of area under the concentration-time curve to minimal inhibitory effect (r2=0.90). Conclusion Induction of an efflux-pump that reduces effect to multiple drugs provides an alternative pathway to sequential acquisition of mutations in the development of multiple drug resistance.

Background. Levofloxacin is used for the treatment of multidrug-resistant tuberculosis; however the optimal dose is unknown. Methods. We used the hollow fiber system model of tuberculosis (HFS-TB) to identify 0-24 hour area under the concentration-time curve (AUC 0-24) to minimum inhibitory concentration (MIC) ratios associated with maximal microbial kill and suppression of acquired drug resistance (ADR) of Mycobacterium tuberculosis (Mtb). Levofloxacin-resistant isolates underwent whole-genome sequencing. Ten thousands patient Monte Carlo experiments (MCEs) were used to identify doses best able to achieve the HFS-TBderived target exposures in cavitary tuberculosis and tuberculous meningitis. Next, we used an ensemble of artificial intelligence (AI) algorithms to identify the most important predictors of sputum conversion, ADR, and death in Tanzanian patients with pulmonary multidrug-resistant tuberculosis treated with a levofloxacin-containing regimen. We also performed probit regression to identify optimal levofloxacin doses in Vietnamese tuberculous meningitis patients. Results. In the HFS-TB, the AUC 0-24 /MIC associated with maximal Mtb kill was 146, while that associated with suppression of resistance was 360. The most common gyrA mutations in resistant Mtb were Asp94Gly, Asp94Asn, and Asp94Tyr. The minimum dose to achieve target exposures in MCEs was 1500 mg/day. AI algorithms identified an AUC 0-24 /MIC of 160 as predictive of microbiologic cure, followed by levofloxacin 2-hour peak concentration and body weight. Probit regression identified an optimal dose of 25 mg/kg as associated with >90% favorable response in adults with pulmonary tuberculosis. Conclusions. The levofloxacin dose of 25 mg/kg or 1500 mg/day was adequate for replacement of high-dose moxifloxacin in treatment of multidrug-resistant tuberculosis.