The Relationship Between Drug Concentration in Tuberculosis Lesions, Epithelial Lining Fluid, and Clinical Outcomes

Pharmacokinetic Considerations for Optimizing Inhaled Spray-Dried Pyrazinoic Acid Formulations

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), remains a leading cause of death with 1.6 million deaths worldwide reported in 2021. Oral pyrazinamide (PZA) is an integral part of anti-TB regimens, but its prolonged use has the potential to drive the development of PZA-resistant Mtb. PZA is converted to the active moiety pyrazinoic acid (POA) by the Mtb pyrazinamidase encoded by pncA, and mutations in pncA are associated with the majority of PZA resistance. Conventional oral and parenteral therapies may result in subtherapeutic exposure in the lung; hence, direct pulmonary administration of POA may provide an approach to rescue PZA efficacy for treating pncA-mutant PZA-resistant Mtb. The objectives of the current study were to (i) develop novel dry powder POA formulations, (ii) assess their feasibility for pulmonary delivery using physicochemical characterization, (iii) evaluate their pharmacokinetics (PK) in the guinea pig model, and (iv) develop a mechanism-based pharmacokinetic model (MBM) using in vivo PK data to select a formulation providing adequate exposure in epithelial lining fluid (ELF) and lung tissue. We developed three POA formulations for pulmonary delivery and characterized their PK in plasma, ELF, and lung tissue following passive inhalation in guinea pigs. Additionally, the PK of POA following oral, intravenous, and intratracheal administration was characterized in guinea pigs. The MBM was used to simultaneously model PK data following administration of POA and its formulations via the different routes. The MBM described POA PK well in plasma, ELF, and lung tissue. Physicochemical analyses and MBM predictions suggested that POA maltodextrin was the best among the three formulations and an excellent candidate for further development as it has: (i) the highest ELF-to-plasma exposure ratio (203) and lung tissue-to-plasma exposure ratio (30.4) compared with POA maltodextrin and leucine (75.7/16.2) and POA leucine salt (64.2/19.3) and (ii) the highest concentration in ELF (CmaxELF: 171 nM) within 15.5 min, correlating with a fast transfer into ELF after pulmonary administration (KPM: 22.6 1/h). The data from the guinea pig allowed scaling, using the MBM to a human dose of POA maltodextrin powder demonstrating the potential feasibility of an inhaled product.

Determining the Delamanid Pharmacokinetics/Pharmacodynamics Susceptibility Breakpoint Using Monte Carlo Experiments

Antimicrobial susceptibility testing, based on clinical breakpoints that incorporate pharmacokinetics/pharmacodynamics (PK/PD) and clinical outcomes, is becoming a new standard in guiding individual patient therapy as well as for drug resistance surveillance. However, for most antituberculosis drugs, breakpoints are instead defined by the epidemiological cutoff values of the MIC of phenotypically wild-type strains irrespective of PK/PD or dose. In this study, we determined the PK/PD breakpoint for delamanid by estimating the probability of target attainment for the approved dose administered at 100 mg twice daily using Monte Carlo experiments. We used the PK/PD targets (0- to 24-h area under the concentration-time curve to MIC) identified in a murine chronic tuberculosis model, hollow fiber system model of tuberculosis, early bactericidal activity studies of patients with drug-susceptible tuberculosis, and population pharmacokinetics in patients with tuberculosis. At the MIC of 0.016 mg/L, determined using Middlebrook 7H11 agar, the probability of target attainment was 100% in the 10,000 simulated subjects. The probability of target attainment fell to 25%, 40%, and 68% for PK/PD targets derived from the mouse model, the hollow fiber system model of tuberculosis, and patients, respectively, at the MIC of 0.031 mg/L. This indicates that an MIC of 0.016 mg/L is the delamanid PK/PD breakpoint for delamanid at 100 mg twice daily. Our study demonstrated that it is feasible to use PK/PD approaches to define a breakpoint for an antituberculosis drug.

Pharmacokinetic considerations for optimizing inhaled spray-dried pyrazinoic acid formulations

Tuberculosis (TB), caused by Mycobacterium tuberculosis ( Mtb ), remains a leading cause of death with 1.6 million deaths worldwide reported in 2021. Oral pyrazinamide (PZA) is an integral part of anti-TB regimens, but its prolonged use has the potential to drive development of PZA resistant Mtb . PZA is converted to the active moiety pyrazinoic acid (POA) by the Mtb pyrazinamidase encoded by pncA , and mutations in pncA are associated with the majority of PZA resistance. Conventional oral and parenteral therapies may result in subtherapeutic exposure in the lung, hence direct pulmonary administration of POA may provide an approach to rescue PZA efficacy for treating pncA- mutant PZA-resistant Mtb . The objectives of the current study were to i) develop novel dry powder POA formulations ii) assess their feasibility for pulmonary delivery using physicochemical characterization, iii) evaluate their pharmacokinetics (PK) in the guinea pig model and iv) develop a mechanism based pharmacokinetic model (MBM) using in vivo PK data to select a formulation providing adequate exposure in epithelial lining fluid (ELF) and lung tissue. We developed three POA formulations for pulmonary delivery and characterized their PK in plasma, ELF, and lung tissue following passive inhalation in guinea pigs. Additionally, the PK of POA following oral, intravenous and intratracheal administration was characterized in guinea pigs. The MBM was used to simultaneously model PK data following administration of POA and its formulations via the different routes. The MBM described POA PK well in plasma, ELF and lung tissue. Physicochemical analyses and MBM predictions suggested that POA maltodextrin was the best among the three formulations and an excellent candidate for further development as it has: (i) the highest ELF-to-plasma exposure ratio (203) and lung tissue-to-plasma exposure ratio (30.4) compared with POA maltodextrin and leucine (75.7/16.2) and POA leucine salt (64.2/19.3); (ii) the highest concentration in ELF ( Cmac ELF : 171 nM) within 15.5 minutes, correlating with a fast transfer into ELF after pulmonary administration ( k PM : 22.6 1/h). The data from the guinea pig allowed scaling, using the MBM to a human dose of POA maltodextrin powder demonstrating the potential feasibility of an inhaled product.

Table of Contents TOC/Abstract Graphic

Intensified Antituberculosis Therapy Regimen Containing Higher Dose Rifampin for Tuberculous Meningitis: A Systematic Review and Meta-Analysis

Background

Tuberculous meningitis is difficult to diagnose and is associated with high mortality. Recently, several studies evaluated the intensified regimen containing higher dose rifampin to treat tuberculous meningitis. However, this topic remains to be concluded. Therefore, this systematic review and meta-analysis was conducted to evaluate pharmacokinetics parameters, safety, and survival benefits of high-dose rifampin for tuberculous meningitis.

Method

Data were searched from PubMed, EMBASE, The Cochrane Library, and Web of Science for studies describing an antituberculosis regimen including a higher dose of rifampin for patients with tuberculous meningitis. The quality of eligible studies was evaluated via The Cochrane Risk of Bias Tool. The meta-analysis was performed by Review Manager 5.3 software, the synthesis of the data was shown in mean difference (MD) or relative risk (RR), and 95% confidence intervals (CIs).

Results

There were six randomized control trails included in this meta-analysis. The results showed that the concentration in plasma and cerebrospinal fluid (CSF) were significantly higher in the intervention group than the standard group [MD = 22.08, 95%CI (16.24, 27.92), p < 0.00001; MD = 0.74, 95%CI (0.42, 1.05), p < 0.00001], as well as the area under the time concentration curve between 0 and 24 h (AUC₀₋₂₄) of rifampin [MD 203.56, 95%CI (153.07, 254.05), p < 0.00001] in plasma, but the overall survival did not improve [RR = 0.92, 95%CI (0.67, 1.26), p = 0.61]. For adverse events, the results showed a statistically significant lower incidence of hypersensitivity compared with the intervention group [RR = 1.72, 95%CI (1.13, 2.62), p = 0.01]. Fortunately, other common adverse drug reactions such as liver injury, neurological events, myelosuppression, and cardiotoxicity had no significant increase [RR = 0.98, 95%CI (0.77, 1.26), p = 0.90; RR = 1.10, 95%CI (0.94, 1.30), p = 0.23; RR = 0.82, 95%CI (0.59, 1.13), p = 0.22; RR = 1.11, 95%CI (0.66, 1.86), p = 0.70].

Conclusion

This meta-analysis suggested that the intensified treatment regimen including a higher dose of rifampin significantly increased the rifampin concentration both in the plasma and CSF, and it was safe in patients with tuberculous meningitis, but resulted in no improvement in survival rates.