Evaluation of Ceftriaxone Plus Avibactam in an Intracellular Hollow Fiber Model of Tuberculosis: Implications for the Treatment of Disseminated and Meningeal Tuberculosis in Children.

BACKGROUND: Ceftazidime-avibactam is an effective agent for the treatment of tuberculosis (TB) but requires frequent administration because of a short half-life. Due to a longer half-life, ceftriaxone could allow intermittent dosing. METHODS: First, we identified the MIC of ceftriaxone with 15 mg/L avibactam in 30 clinical Mycobacterium tuberculosis isolates. Next, 2 ceftriaxone exposure-effect studies in the intracellular hollow fiber model of TB (HFS-TB) that mimics disseminated disease in young children, were performed. Ceftriaxone was administered once or twice daily for 28 days to explore percentage of time that the concentration persisted above MIC (%TMIC) ranging from 0 to 100%. In a third HFS-TB experiment, the "double cephalosporin" regimen of ceftazidime-ceftriaxone-avibactam was examined and analyzed using Bliss Independence. CONCLUSION: The MIC99 of the clinical strains was 32 mg/L, in the presence of 15 mg/L avibactam. Ceftriaxone %TMIC <42 had no microbial effect in the HFS-TB, %TMIC >54% demonstrated a 4.1 log10 colony-forming units per milliliter M. tuberculosis kill, while %TMIC mediating Emax was 68%. The "double cephalosporin" combination was highly synergistic. Monte Carlo experiments of 10,000 subjects identified the optimal ceftriaxone dose as 100 mg/kg twice a day. CONCLUSION: The combination of ceftriaxone-avibactam at 100 mg/kg could achieve Emax in >90% of children. The ceftriaxone potent activity M. tuberculosis could potentially shorten therapy in children with disseminated TB.

Repurposing drugs for treatment of Mycobacterium abscessus: a view to a kill.

BACKGROUND: The current treatment regimens recommended for Mycobacterium abscessus subspecies abscessus (Mab) pulmonary disease are not effective. We identified 16 drugs with potential to build new regimens, translating to 560 possible three-drug combination regimens. OBJECTIVES: To determine MICs and efficacy of drugs from different antibiotic classes for treatment against Mab, in order to winnow down the potential drugs for combination therapy to tractable numbers, for future use in hollow-fibre studies. METHODS: The MICs of levofloxacin, minocycline, meropenem, imipenem, tedizolid, bedaquiline, azithromycin, clarithromycin, amikacin, vancomycin, delafloxacin, tebipenem/avibactam and omadacycline were determined for 20 Mab isolates. In addition, concentration-response studies with tedizolid, bedaquiline, clarithromycin, amikacin, tebipenem/avibactam, cefdinir, faropenem, omadacycline and daunorubicin were performed and data were fitted to the inhibitory sigmoid Emax model. Efficacy was defined as maximal kill, expressed as cfu/mL kill below day 0 burden. RESULTS: The lowest MICs among the 13 antibiotics were of bedaquiline, tebipenem/avibactam and omadacycline. The antibiotics that killed Mab below the day 0 burden were the anticancer agent daunorubicin (3.36 log10 cfu/mL), cefdinir (1.85 log10 cfu/mL), faropenem (2.48 log10 cfu/mL) and tebipenem/avibactam (1.71 log10 cfu/mL kill). The EC50 values of these drugs were 11.67, 9.52, 48.2 and 0.33 mg/L, respectively, below peak concentrations of these drugs. CONCLUSIONS: The low MICs and efficacy at clinically achievable concentrations mean that tebipenem/avibactam, daunorubicin, omadacycline and bedaquiline give a view of components of a three-drug regimen likely to effectively kill Mab. We propose pharmacokinetic/pharmacodynamic studies to identify such a regimen and the doses to be combined.

Duration of pretomanid/moxifloxacin/pyrazinamide therapy compared with standard therapy based on time-to-extinction mathematics.

OBJECTIVES: Animal models have suggested that the combination of pretomanid with pyrazinamide and moxifloxacin (PaMZ) may shorten TB therapy duration to 3-4 months. Here, we tested that in the hollow-fibre system model of TB (HFS-TB). METHODS: A series of HFS-TB experiments were performed to compare the kill rates of the PaMZ regimen with the standard three-drug combination therapy. HFS-TB experiments were performed with bacilli in log-phase growth treated for 28 days, intracellular bacilli treated daily for 28 days and semi-dormant Mycobacterium tuberculosis treated with daily therapy for 56 days for sterilizing effect. Next, time-to-extinction equations were employed, followed by morphism transformation and Latin hypercube sampling, to determine the proportion of patients who achieved a time to extinction of 3, 4 or 6 months with each regimen. RESULTS: Using linear regression, the HFS-TB sterilizing effect rates of the PaMZ regimen versus the standard-therapy regimen during the 56 days were 0.18 (95% credible interval=0.13-0.23) versus 0.15 (95% credible interval=0.08-0.21) log10 cfu/mL/day, compared with 0.16 (95% credible interval=0.13-0.18) versus 0.11 (95% credible interval=0.09-0.13) log10 cfu/mL/day in the Phase II clinical trial, respectively. Using time-to-extinction and Latin hypercube sampling modelling, the expected percentages of patients in which the PaMZ regimen would achieve sterilization were 40.37% (95% credible interval=39.1-41.34) and 72.30% (95% credible interval=71.41-73.17) at 3 and 4 months duration of therapy, respectively, versus 93.67% (95% credible interval=93.18-94.13) at 6 months for standard therapy. CONCLUSIONS: The kill rates of the PaMZ regimen were predicted to be insufficient to achieve cure in less than 6 months in most patients.

Once-a-week tigecycline for the treatment of drug-resistant TB.

BACKGROUND: MDR-TB and XDR-TB have poor outcomes. OBJECTIVES: To examine the efficacy of tigecycline monotherapy in the hollow fibre system model of TB. METHODS: We performed pharmacokinetic/pharmacodynamic studies using tigecycline human-like concentration-time profiles in the hollow fibre system model of TB in five separate experiments using Mycobacterium tuberculosis in log-phase growth or as semi-dormant or intracellular bacilli, as monotherapy. We also compared efficacy with the isoniazid/rifampicin/pyrazinamide combination (standard therapy). We then applied extinction mathematics, morphisms and Latin hypercube sampling to identify duration of therapy with tigecycline monotherapy. RESULTS: The median tigecycline MIC for 30 M. tuberculosis clinical and laboratory isolates (67% MDR/XDR) was 2 mg/L. Tigecycline monotherapy was highly effective in killing M. tuberculosis in log-phase-growth and semi-dormant and intracellular M. tuberculosis. Once-a-week dosing had the same efficacy as daily therapy for the same cumulative dose; thus, tigecycline efficacy was linked to the AUC0-24/MIC ratio. Tigecycline replacement by daily minocycline after 4 weeks of therapy was effective in sterilizing bacilli. The AUC0-24/MIC ratio associated with optimal kill was 42.3. Tigecycline monotherapy had a maximum sterilizing effect (day 0 minus day 28) of 3.06 ±âŸ0.20 log10 cfu/mL (r2 = 0.92) compared with 3.92 ±âŸ0.45 log10 cfu/mL (r2 = 0.80) with optimized standard therapy. In our modelling, at a tigecycline monotherapy duration of 12 months, the proportion of patients with XDR-TB who reached bacterial population extinction was 64.51%. CONCLUSIONS: Tigecycline could cure patients with XDR-TB or MDR-TB who have failed recommended therapy. Once-a-week tigecycline could also replace second-line injectables in MDR-TB regimens.

Multiparameter Responses to Tedizolid Monotherapy and Moxifloxacin Combination Therapy Models of Children With Intracellular Tuberculosis.

Background: Children are often neglected during early development of antituberculosis agents, and most receive treatment after it is first tested in adults. However, very young children have tuberculosis that differs in many respects from adult cavitary pneumonia and could have different toxicity profiles to drugs. Linezolid is effective against intracellular tuberculosis, a common manifestation in young children. However, linezolid has considerable toxicity due to inhibition of mitochondrial enzymes. Tedizolid could be a replacement if it shows equal efficacy and reduced toxicity. Methods: We performed tedizolid dose-effect studies in the hollow fiber system model of intracellular tuberculosis. We measured linezolid concentrations, colony-forming units (CFU), time-to-positivity, and monocyte viability and performed RNA sequencing on infected cells collected from repetitive sampling of each system. We also compared efficacy of tedizolid vs linezolid and vs tedizolid-moxifloxacin combination. Results: There was no downregulation of mitochondrial enzyme genes, with a tedizolid 0-24 hour area under the concentration-time curve (AUC0-24) of up to 90 mg*h/L. Instead, high exposures led to increased mitochondrial gene expression and monocyte survival. The AUC0-24 to minimum inhibitory concentration ratio associated with 80% of maximal bacterial kill (EC80) was 184 by CFU/mL (r2 = 0.96) and 189 by time-to-positivity (r2 = 0.99). Tedizolid EC80 killed 4.0 log10 CFU/mL higher than linezolid EC80. The tedizolid-moxifloxacin combination had a bacterial burden elimination rate constant of 0.27 ± 0.05 per day. Conclusions: Tedizolid demonstrated better efficacy than linezolid, without the mitochondrial toxicity gene or cytotoxicity signatures encountered with linezolid. Tedizolid-moxifloxacin combination had a high bacterial elimination rate.

Antibacterial and Sterilizing Effect of Benzylpenicillin in Tuberculosis.

The modern chemotherapy era started with Fleming's discovery of benzylpenicillin. He demonstrated that benzylpenicillin did not kill Mycobacterium tuberculosis In this study, we found that >64 mg/liter of static benzylpenicillin concentrations killed 1.16 to 1.43 log10 CFU/ml below starting inoculum of extracellular and intracellular M. tuberculosis over 7 days. When we added the ß-lactamase inhibitor avibactam, benzylpenicillin maximal kill (Emax) of extracellular log-phase-growth M. tuberculosis was 6.80 ± 0.45 log10 CFU/ml at a 50% effective concentration (EC50) of 15.11 ± 2.31 mg/liter, while for intracellular M. tuberculosis it was 2.42 ± 0.14 log10 CFU/ml at an EC50 of 6.70 ± 0.56 mg/liter. The median penicillin (plus avibactam) MIC against South African clinical M. tuberculosis strains (80% either multidrug or extensively drug resistant) was 2 mg/liter. We mimicked human-like benzylpenicillin and avibactam concentration-time profiles in the hollow-fiber model of tuberculosis (HFS-TB). The percent time above the MIC was linked to effect, with an optimal exposure of ≥65%. At optimal exposure in the HFS-TB, the bactericidal activity in log-phase-growth M. tuberculosis was 1.44 log10 CFU/ml/day, while 3.28 log10 CFU/ml of intracellular M. tuberculosis was killed over 3 weeks. In an 8-week HFS-TB study of nonreplicating persistent M. tuberculosis, penicillin-avibactam alone and the drug combination of isoniazid, rifampin, and pyrazinamide both killed >7.0 log10 CFU/ml. Monte Carlo simulations of 10,000 preterm infants with disseminated disease identified an optimal dose of 10,000 U/kg (of body weight)/h, while for pregnant women or nonpregnant adults with pulmonary tuberculosis the optimal dose was 25,000 U/kg/h, by continuous intravenous infusion. Penicillin-avibactam should be examined for effect in pregnant women and infants with drug-resistant tuberculosis, to replace injectable ototoxic and teratogenic second-line drugs.