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Background Individual pharmacokinetic variability is a driver of poor tuberculosis (TB) treatment outcomes. We developed a method for measurement of rifampin concentrations by urine colorimetry and a mobile phone photographic application to predict clinically important serum rifampin pharmacokinetic measurements in children treated for TB. Methods Among spiked urine samples, colorimetric assay performance was tested with conventional spectrophotometric and the mobile phone/light box methods under various environmental and biologic conditions. Urine rifampin absorbance (Abs) was then determined from timed specimens from children treated for TB in Tanzania, and compared to serum pharmacokinetic measurements collected throughout the dosing interval. Results Both the mobile phone/light box and spectrophotometry demonstrated excellent correlation across a wide range of urine rifampin concentrations (7.8–1000 mg/L) in intra- and interday trials, 24-hour exposure to ambient light or darkness, and varying urinalysis profiles (all r ≥ 0.98). In 12 Tanzanian children, the urine mobile phone/light box measurement and serum peak concentration (Cmax) were significantly correlated (P = .004). Using a Cmax target of 8 mg/L, the area under the receiver operating characteristic curve was 80.1% (range, 47.2%–100%). A urine mobile phone/light box threshold of 50 Abs correctly classified all patients (n = 6) with serum measurements below target. Conclusions The urine colorimetry with mobile phone/light box assay accurately measured rifampin absorbance in varying environmental and biological conditions that may be observed clinically. Among children treated for TB, the assay was sensitive for detection of low rifampin serum concentrations. Future work will identify the optimal timing for urine collection, and operationalize use in TB-endemic settings.

Objective: There is considerable uncertainty regarding the optimal use of rifampicin for the treatment of tuberculous (TB) meningitis. A pharmacokinetic modeling and simulation study of rifampicin concentrations in cerebrospinal fluid (CSF) during TB meningitis treatment was performed in this study. Methods: Parameters for rifampicin pharmacokinetics in CSF were estimated using individual-level rifampicin pharmacokinetic data, and the model was externally validated in three separate patient cohorts. Monte Carlo simulations of rifampicin serum and CSF concentrations were performed. The area under the rifampicin CSF concentration-versus-time curve during 24 h (AUC0–24) relative to the minimum inhibitory concentration (MIC) served as the pharmacodynamic target. Results: Across all simulated patients on the first treatment day, 85% attained the target AUC0–24/MIC ratio of 30 under a weight-based dosing scheme approximating 10 mg/kg. At the rifampicin MIC of 0.5 mg/l, the probability of AUC0–24/MIC target attainment was 26%. With an intensified dosing strategy corresponding to 20 mg/kg, target attainment increased to 99%, including 93% with a MIC of 0.5 mg/l. Conclusions: Under standard dosing guidelines, few TB meningitis patients would be expected to attain therapeutic rifampicin exposures in CSF when the MIC is ≥0.5 mg/l. Either downward adjustment of the rifampicin MIC breakpoint in the context of TB meningitis, or intensified rifampicin dosing upwards of 20 mg/kg/day, would reflect the likelihood of pharmacodynamic target attainment in CSF. Keywords: Tuberculosis, Meningitis, Tuberculous meningitis, Pharmacokinetics, Pharmacodynamics

Background: The potential for hepatotoxicity during isoniazid-based tuberculosis (TB) treatment presents a major challenge for TB control programs worldwide. We sought to determine whether pharmacokinetic exposures of isoniazid and its metabolites were related to cellular oxidation/reduction status and downstream markers of oxidative DNA damage. Methods: We performed intensive pharmacokinetic sampling among isoniazid-treated patients to determine the relative plasma exposures of isoniazid, acetylisoniazid, hydrazine, and acetylhydrazine. Physiologically-based pharmacokinetic modeling was used to estimate liver tissue exposures during a 24-hour dosing interval for each compound. We experimentally treated HepG2 cells with isoniazid and metabolites at equimolar concentrations corresponding to these exposures for 7, 14, and 28 day periods, and performed assays related to redox imbalance and oxidative DNA damage at each timepoint. We related a urine marker of oxidative DNA damage to serum isoniazid pharmacokinetic exposures and pharmacogenetics in a clinical study. Results: Among isoniazid-treated patients, serum concentrations of hydrazine and isoniazid concentrations were highly correlated. At equimolar concentrations that approximated hepatic tissue exposures during a 24-hour dosing interval, hydrazine demonstrated the highest levels of redox imbalance, mitochondrial injury, and oxidative DNA damage over a 28-day treatment period. In a clinical validation study of isoniazid-treated TB patients, peak isoniazid serum concentrations were positively associated with a urine biomarker of oxidative DNA damage. Conclusions: Isoniazid and its metabolites share the potential for oxidative cellular damage, with the greatest effects observed for hydrazine. Future studies should investigate the clinical consequences of oxidative stress with regards to clinical episodes of drug induced liver injury during isoniazid treatment.

BackgroundThe potential for hepatotoxicity during isoniazid-based tuberculosis (TB) treatment presents a major challenge for TB control programs worldwide. We sought to determine whether pharmacokinetic exposures of isoniazid and its metabolites were related to cellular oxidation/reduction status and downstream markers of oxidative DNA damage.MethodsWe performed intensive pharmacokinetic sampling among isoniazid-treated patients to determine the relative plasma exposures of isoniazid, acetylisoniazid, hydrazine, and acetylhydrazine. Physiologically-based pharmacokinetic modeling was used to estimate liver tissue exposures during a 24-hour dosing interval for each compound. We experimentally treated HepG2 cells with isoniazid and metabolites at equimolar concentrations corresponding to these exposures for 7, 14, and 28 day periods, and performed assays related to redox imbalance and oxidative DNA damage at each timepoint. We related a urine marker of oxidative DNA damage to serum isoniazid pharmacokinetic exposures and pharmacogenetics in a clinical study.ResultsAmong isoniazid-treated patients, serum concentrations of hydrazine and isoniazid concentrations were highly correlated. At equimolar concentrations that approximated hepatic tissue exposures during a 24-hour dosing interval, hydrazine demonstrated the highest levels of redox imbalance, mitochondrial injury, and oxidative DNA damage over a 28-day treatment period. In a clinical validation study of isoniazid-treated TB patients, peak isoniazid serum concentrations were positively associated with a urine biomarker of oxidative DNA damage.ConclusionsIsoniazid and its metabolites share the potential for oxidative cellular damage, with the greatest effects observed for hydrazine. Future studies should investigate the clinical consequences of oxidative stress with regards to clinical episodes of drug induced liver injury during isoniazid treatment.

Objectives: Pyrazinamide is a key drug in the first-line treatment regimen for tuberculosis, with a potent sterilizing effect. Although low pyrazinamide peak serum concentrations (Cmax) are associated with poor treatment outcomes, many resource-constrained settings do not have sufficient laboratory capacity to support therapeutic drug monitoring (TDM). The objective of this study was to determine whether a colorimetric test of urine can identify tuberculosis patients with adequate pyrazinamide exposures, as defined by serum Cmax above a target threshold. Methods: In the derivation study of healthy volunteers, three dose sizes of pyrazinamide were evaluated, and intensive pharmacokinetic blood sampling was performed over an 8-h period, with a timed urine void at 4 h post-dosing. Pyrazinamide in urine was isolated by spin column centrifugation with an exchange resin, followed by colorimetric analysis; the absorbance peak at 495 nm was measured. The urine assay was then evaluated in a study of 39 HIV/tuberculosis patients in Botswana enrolled in an intensive pharmacokinetic study. Receiver operating characteristics (ROC) curves were used to measure diagnostic accuracy. The guideline-recommended pyrazinamide serum Cmax target of 35 mg/l was evaluated in the primary analysis; this target was found to be predictive of favorable outcomes in a clinical study. Following this, a higher serum Cmax target of 58 mg/l was evaluated in the secondary analysis. Results: At the optimal cut-off identified in the derivation sample, the urine colorimetric assay was 97% sensitive and 50% specific to identify 35 of 39 HIV/tuberculosis patients with pharmacokinetic target attainment, with an area under the ROC curve of 0.81 (95% confidence interval 0.60–0.97). Diagnostic accuracy was lower at the 58 mg/l serum Cmax target, with an area under the ROC curve of 0.68 (95% confidence interval 0.48–0.84). Men were less likely than women to attain either serum pharmacokinetic target. Conclusions: The urine colorimetric assay was sensitive but not specific for the detection of adequate pyrazinamide pharmacokinetic exposures among HIV/tuberculosis patients in a high-burden setting. Keywords: Tuberculosis, Pyrazinamide, Pharmacokinetics, Human immunodeficiency virus, Point-of-care testing

Background. Rifampin malabsorption is frequently observed in tuberculosis patients coinfected with human immunodeficiency virus (HIV) but cannot be predicted by patient factors such as CD4+ T cell count or HIV viral load. Methods. We sought to describe the relationship between HIV-associated immune activation, measures of gut absorptive capacity and permeability, and rifampin pharmacokinetic parameters in a pilot study of 6 HIV-infected, tuberculosis-uninfected patients who were naïve to antiretroviral therapy. Results. The median rifampin area under the concentration-versus-time curve during the 8-hour observation period was 42.8 mg·hr/L (range: 21.2 to 57.6), with a median peak concentration of 10.1 mg/L (range: 5.3 to 12.5). We observed delayed rifampin absorption, with a time to maximum concentration greater than 2 hours, in 2 of 6 participants. There was a trend towards increased plasma concentrations of sCD14, a marker of monocyte activation in response to bacterial translocation, among participants with delayed rifampin absorption compared to participants with rapid absorption (p=0.06). Conclusions. Delayed rifampin absorption may be associated with elevated markers of bacterial translocation among HIV-infected individuals naïve to antiretroviral therapy. This trial is registered with NCT01845298.

Background The cost and complexity of current approaches to therapeutic drug monitoring during tuberculosis (TB) therapy limits widespread use in areas of greatest need. We sought to determine whether urine colorimetry could have a novel application as a form of therapeutic drug monitoring during anti-TB therapy. Methods Among healthy volunteers, we evaluated 3 dose sizes of rifampin (150 mg, 300 mg, and 600 mg), performed intensive pharmacokinetic sampling, and collected a timed urine void at 4 h post-dosing. The absorbance peak at 475 nm was measured after rifamycin extraction. The optimal cutoff was evaluated in a study of 39 HIV/TB patients undergoing TB treatment in Botswana. Results In the derivation study, a urine colorimetric assay value of 4.0 × 10−2 Abs, using a timed void 4 h after dosing, demonstrated a sensitivity of 92 % and specificity of 60 % to detect a peak rifampin concentration (Cmax) under 8 mg/L, with an area under the ROC curve of 0.92. In the validation study, this cutoff was specific (100 %) but insensitive (28 %). We observed similar test characteristics for a target Cmax target of 6.6 mg/L, and a target area under the drug concentration-versus-time curve (AUC0–8) target of 24.1 mg•hour/L. Conclusions The urine colorimetric assay was specific but insensitive to detect low rifampin serum concentrations among HIV/TB patients. In future work we will attempt to optimize sampling times and assay performance, with the goal of delivering a method that can translate into a point-of-care assessment of rifampin exposure during anti-TB therapy.