Pharmacokinetic assessment of rifampicin and des-acetyl rifampicin in carbon tetrachloride induced liver injury model in Wistar rats.

OBJECTIVES: Preclinical evidence is needed to assess drug-metabolite behaviour in compromised liver function for developing the best antitubercular treatment (ATT) re-introduction regimen in drug-induced liver injury (DILI). The pharmacokinetic behavior of rifampicin (RMP) and its active metabolite des-acetyl-rifampicin (DARP) in DILI's presence is unknown. To study the pharmacokinetic behavior of RMP and DARP in the presence of carbon tetrachloride (CCl4) plus ATT-DILI in rats. METHODS: Thirty rats used in the experiment were divided equally into six groups. We administered a single 0.5 mL/kg CCl4 intraperitoneal injection in all rats. Groups II, III, IV, and V were started on daily oral RMP alone, RMP plus isoniazid (INH), RMP plus pyrazinamide (PZA), and the three drugs INH, RMP, and PZA together, respectively, for 21-days subsequently. Pharmacokinetic (PK) sampling was performed at 0, 0.5, 1, 3, 6, 12, and 24 h post-dosing on day 20. We monitored LFT at baseline on days-1, 7, and 21 and sacrificed the rats on the last day of the experiment. RESULTS: ATT treatment sustained the CCl4-induced liver injury changes. A significant rise in mean total bilirubin levels was observed in groups administered rifampicin. The triple drug combination group demonstrated 1.43- and 1.84-times higher area-under-the-curve values of RMP (234.56±30.66 vs. 163.55±36.14 µg h/mL) and DARP (16.15±4.50 vs. 8.75±2.79 µg h/mL) compared to RMP alone group. Histological and oxidative stress changes supported underlying liver injury and PK alterations. CONCLUSIONS: RMP metabolism inhibition by PZA, more than isoniazid, was well preserved in the presence of underlying liver injury.

Moxifloxacin Pharmacokinetics, Cardiac Safety, and Dosing for the Treatment of Rifampicin-Resistant Tuberculosis in Children.

BACKGROUND: Moxifloxacin is a recommended drug for rifampin-resistant tuberculosis (RR-TB) treatment, but there is limited pediatric pharmacokinetic and safety data, especially in young children. We characterize moxifloxacin population pharmacokinetics and QT interval prolongation and evaluate optimal dosing in children with RR-TB. METHODS: Pharmacokinetic data were pooled from 2 observational studies in South African children with RR-TB routinely treated with oral moxifloxacin once daily. The population pharmacokinetics and Fridericia-corrected QT (QTcF)-interval prolongation were characterized in NONMEM. Pharmacokinetic simulations were performed to predict expected exposure and optimal weight-banded dosing. RESULTS: Eighty-five children contributed pharmacokinetic data (median [range] age of 4.6 [0.8-15] years); 16 (19%) were aged <2 years, and 8 (9%) were living with human immunodeficiency virus (HIV). The median (range) moxifloxacin dose on pharmacokinetic sampling days was 11 mg/kg (6.1 to 17). Apparent clearance was 6.95 L/h for a typical 16-kg child. Stunting and HIV increased apparent clearance. Crushed or suspended tablets had faster absorption. The median (range) maximum change in QTcF after moxifloxacin administration was 16.3 (-27.7 to 61.3) ms. No child had QTcF ≥500 ms. The concentration-QTcF relationship was nonlinear, with a maximum drug effect (Emax) of 8.80 ms (interindividual variability = 9.75 ms). Clofazimine use increased Emax by 3.3-fold. Model-based simulations of moxifloxacin pharmacokinetics predicted that current dosing recommendations are too low in children. CONCLUSIONS: Moxifloxacin doses above 10-15 mg/kg are likely required in young children to match adult exposures but require further safety assessment, especially when coadministered with other QT-prolonging agents.

Investigating the Utility of Humanized Pregnane X Receptor-Constitutive Androstane Receptor-CYP3A4/7 Mouse Model to Assess CYP3A-Mediated Induction.

Clinical induction liability is assessed with human hepatocytes. However, underpredictions in the magnitude of clinical induction have been reported. Unfortunately, in vivo studies in animals do not provide additional insight because of species differences in drug metabolizing enzymes and their regulatory pathways. To circumvent this limitation, transgenic animals expressing human orthologs were developed. The aim of this work was to investigate the utility of mouse models expressing human orthologs of pregnane X receptor, constitutive androstane receptor, and CYP3A4/7 (Tg-Composite) in evaluating clinical induction. Rifampin, efavirenz, and pioglitazone, which were employed to represent strong, moderate, and weak inducers, were administered at multiple doses to Tg-Composite animals. In vivo CYP3A activity was monitored by measuring changes in the exposure of the CYP3A probe substrate triazolam. After the in vivo studies, microsomes were prepared from their livers to measure changes of in vitro CYP3A4 activity. In both in vivo and in vitro, distinction of clinic induction was recapitulated as rifampin yielded the greatest inductive effect followed by efavirenz and pioglitazone. Interestingly, with rifampin, in vivo CYP3A activity was approximately 4-fold higher than in vitro activity. Conversely, there was no difference between in vivo and in vitro CYP3A activity with efavirenz. These findings are consistent with the report that, although rifampin exhibits differential inductive effects between the intestines and liver, efavirenz does not. These data highlight the promise of transgenic models, such as Tg-Composite, to complement human hepatocytes to enhance the translatability of clinical induction as well as become a powerful tool to further study mechanisms of drug disposition. SIGNIFICANCE STATEMENT: Underprediction of the magnitude of clinical induction when using human hepatocytes has been reported, and transgenic models may improve clinical translatability. The work presented here showcases the human orthologs of pregnane X receptor, constitutive androstane receptor, and CYP3A4/7 model, which was able to recapitulate the magnitude of clinical induction and to differentiate tissue-dependent induction observed with rifampin but not with efavirenz. These results not only foreshadow the potential application of such transgenic models in assessing clinical induction but also in further investigation of the mechanism of drug disposition.

A model-based analysis identifies differences in phenotypic resistance between in vitro and in vivo: implications for translational medicine within tuberculosis.

Proper characterization of drug effects on Mycobacterium tuberculosis relies on the characterization of phenotypically resistant bacteria to correctly establish exposure-response relationships. The aim of this work was to evaluate the potential difference in phenotypic resistance in in vitro compared to murine in vivo models using CFU data alone or CFU together with most probable number (MPN) data following resuscitation with culture supernatant. Predictions of in vitro and in vivo phenotypic resistance i.e. persisters, using the Multistate Tuberculosis Pharmacometric (MTP) model framework was evaluated based on bacterial cultures grown with and without drug exposure using CFU alone or CFU plus MPN data. Phenotypic resistance and total bacterial number in in vitro natural growth observations, i.e. without drug, was well predicted by the MTP model using only CFU data. Capturing the murine in vivo total bacterial number and persisters during natural growth did however require re-estimation of model parameter using both the CFU and MPN observations implying that the ratio of persisters to total bacterial burden is different in vitro compared to murine in vivo. The evaluation of the in vitro rifampicin drug effect revealed that higher resolution in the persister drug effect was seen using CFU and MPN compared to CFU alone although drug effects on the other bacterial populations were well predicted using only CFU data. The ratio of persistent bacteria to total bacteria was predicted to be different between in vitro and murine in vivo. This difference could have implications for subsequent translational efforts in tuberculosis drug development.

Individualised dosing algorithm and personalised treatment of high-dose rifampicin for tuberculosis.

AIMS: To propose new exposure targets for Bayesian dose optimisation suited for high-dose rifampicin and to apply them using measured plasma concentrations coupled with a Bayesian forecasting algorithm allowing predictions of future doses, considering rifampicin's auto-induction, saturable pharmacokinetics and high interoccasion variability. METHODS: Rifampicin exposure targets for Bayesian dose optimisation were defined based on literature data on safety and anti-mycobacterial activity in relation to rifampicin's pharmacokinetics i.e. highest plasma concentration up to 24 hours and area under the plasma concentration-time curve up to 24 hours (AUC0-24h ). Targets were suggested with and without considering minimum inhibitory concentration (MIC) information. Individual optimal doses were predicted for patients treated with rifampicin (10 mg/kg) using the targets with Bayesian forecasting together with sparse measurements of rifampicin plasma concentrations and baseline rifampicin MIC. RESULTS: The suggested exposure target for Bayesian dose optimisation was a steady state AUC0-24h of 181-214 h × mg/L. The observed MICs ranged from 0.016-0.125 mg/L (mode: 0.064 mg/L). The predicted optimal dose in patients using the suggested target ranged from 1200-3000 mg (20-50 mg/kg) with a mode of 1800 mg (30 mg/kg, n = 24). The predicted optimal doses when taking MIC into account were highly dependent on the known technical variability of measured individual MIC and the dose was substantially lower compared to when using the AUC0-24h -only target. CONCLUSIONS: A new up-to-date exposure target for Bayesian dose optimisation suited for high-dose rifampicin was derived. Using measured plasma concentrations coupled with Bayesian forecasting allowed prediction of the future dose whilst accounting for the auto-induction, saturable pharmacokinetics and high between-occasion variability of rifampicin.

Attainment of target rifampicin concentrations in cerebrospinal fluid during treatment of tuberculous meningitis.

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.

[Effects of tannins in Galla Chinensis on pharmacokinetics of rifampicin in vivo and in vitro].

This study was aimed to explore the effects of tannins in Galla Chinensis on rifampicin in vivo. In the experiment in vitro, UV spectrophotometry and high performance liquid chromatography (HPLC) were used to investigate the solubility of rifampin in pH 1.3, 6.8, artificial gastric juice environment and artificial intestinal fluid environment as well as the effects of tannins on solubility of rifampin in the above conditions. In the experiment in vivo, the process of rifampicin was studied after intragastric administration of rifampicin and rifampicin+ tannins in Galla Chinensis, and then the pharmacokinetic parameters were calculated. The results showed that rifampicin was constantly precipitated in the artificial gastric juice environment over time, and nearly 85% of the rifampicin was precipitated after 6 hours; it showed a good solubility in the artificial intestinal juice environment. After adding the said tannins, the concentration of rifampicin was decreased significantly in both environments, and the concentration of rifampicin in artificial intestinal juice remained relatively stable, while that in artificial gastric juice remained the original downward trend. The pharmacokinetic parameters displayed that as compared with rifampicin alone, AUC0-t and Cmax were decreased significantly, MRT0-t slowed down significantly, Tmax doubled to 7.0 h and the bioavailability was only 31.65% in rifampicin + tannins in Galla Chinensis group. The experiment indicated rifampicin had a poor solubility in acidic environment and the decrease of bioavailability of rifampicin when in combination with tannin was mainly due to the reduction of rifampicin solubility in intestinal tract by complexation of rifampicin with tannin, thus affecting its absorption in intestinal tract. Therefore, rifampicin and the Chinese herbal medicines or Chinese patent medicines rich in tannin should not be taken simultaneously.

Clofazimine for the Treatment of Mycobacterium kansasii.

Mycobacterium kansasii pulmonary infection is a global problem. Standard combination therapy consists of isoniazid at 300 mg/day, rifampin at 600 mg/day, and ethambutol at 15 mg/kg of body weight/day for 18 months. Coincubation of M. kansasii with different clofazimine concentrations over 7 days in test tubes resulted in a maximal kill (maximum effect [Emax]) of 2.03 log10 CFU/ml below the day 0 bacterial burden. The concentration associated with Emax was 110 times the MIC. Next, the effects of human-like concentration-time profiles of clofazimine human-equivalent doses ranging from 0 to 200 mg daily for 21 days were examined in the hollow-fiber model of intracellular M. kansasii (HFS-Mkn). On day 14, when the clofazimine microbial effect was maximal, the Emax was 2.57 log10 CFU/ml, while the dose associated with Emax was 100 mg/day. However, no dose killed M. kansasii to levels below the day 0 bacterial burden. Thus, the antimicrobial effect of clofazimine monotherapy in the HFS-Mkn was modest. Human-equivalent concentration-time profiles of standard combination therapy and doses were used as comparators in the HFS-Mkn On day 14, standard therapy killed to a level 2.32 log10 CFU/ml below the day 0 bacterial burden. The effect of standard therapy was consistent with a biexponential decline, with kill rate constants of 1.85 per day (half-life = 0.37 days) and 0.06 per day (half-life = 12.76 days) (r2 > 0.99). This means that standard therapy would take 9.3 to 12 months to completely eliminate M. kansasii in the model, which is consistent with clinical observations. This observation for standard therapy means that the modest to poor effect of clofazimine on M. kansasii identified here is likely to be the same in the clinic.

Intermediate Susceptibility Dose-Dependent Breakpoints For High-Dose Rifampin, Isoniazid, and Pyrazinamide Treatment in Multidrug-Resistant Tuberculosis Programs.

Background: Bacterial susceptibility is categorized as susceptible, intermediate-susceptible dose-dependent (ISDD), and resistant. The strategy is to use higher doses of first-line agents in the ISDD category, thereby preserving the use of these drugs. This system has not been applied to antituberculosis drugs. Pharmacokinetic/pharmacodynamic (PK/PD) target exposures, in tandem with Monte Carlo experiments, recently identified susceptibility breakpoints of 0.0312 mg/L for isoniazid, 0.0625 mg/L for rifampin, and 50 mg/L for pyrazinamide. These have been confirmed in clinical studies. Methods: Target attainment studies were carried out using Monte Carlo experiments to investigate whether rifampin, isoniazid, and pyrazinamide dose increases would achieve the PK/PD target in >90% of 10000 patients with tuberculosis caused by bacteria, revealing minimum inhibitory concentrations (MICs) between the proposed and the traditional breakpoints. Results: We found that an isoniazid dose of 900 mg/day identified a new ISDD MIC range of 0.0312-0.25 mg/L and resistance at MIC ≥0.5 mg/L. Rifampin 1800 mg/day would result in an ISDD of 0.0625-0.25 mg/L and resistance at MIC ≥0.5 mg/L. At a dose of pyrazinamide 4 g/day, the ISDD MIC range was 37.5-50 mg/L and resistance at MIC ≥100 mg/L. Based on MIC distributions, 93% (isoniazid), 78% (rifampin), and 27% (pyrazinamide) of isolates would be within the ISDD range. Conclusions: Drug susceptibility testing at 2 concentrations delineating the ISDD range, and subsequently using higher doses, could prevent switching to a more toxic second-line treatment. Confirmatory clinical studies would provide evidence to change treatment guidelines.

Predicting effects of antibiotic combinations using MICs determined at pharmacokinetically derived concentration ratios: in vitro model studies with linezolid- and rifampicin-exposed Staphylococcus aureus.

To predict the effects of combined use of antibiotics on their pharmacodynamics, the susceptibility of Staphylococcus aureus to linezolid-rifampicin combinations was tested at concentration ratios equal to the ratios of 24-area under the concentration-time curve (AUC24) simulated in an in vitro dynamic model. The linezolid MICs in combination with rifampicin decreased 8- to 67-fold. The rifampicin MICs were similar with or without linezolid. The enhanced activity of linezolid combined with rifampicin increased the AUC24/MIC ratios and provided more pronounced antibacterial effects compared with single treatments. The areas between the control growth and time-kill curves (ABBCs) determined in combined and single treatments with linezolid were plotted against AUC24/MIC on the same graph (r2 0.94). These findings suggest that the effects of linezolid-rifampicin combinations can be predicted by AUC24/MICs of linezolid using its MIC determined at pharmacokinetically derived linezolid-to-rifampicin concentration ratios.

Concentration-Dependent Antagonism and Culture Conversion in Pulmonary Tuberculosis.

BACKGROUND: There is scant evidence to support target drug exposures for optimal tuberculosis outcomes. We therefore assessed whether pharmacokinetic/pharmacodynamic (PK/PD) parameters could predict 2-month culture conversion. METHODS: One hundred patients with pulmonary tuberculosis (65% human immunodeficiency virus coinfected) were intensively sampled to determine rifampicin, isoniazid, and pyrazinamide plasma concentrations after 7-8 weeks of therapy, and PK parameters determined using nonlinear mixed-effects models. Detailed clinical data and sputum for culture were collected at baseline, 2 months, and 5-6 months. Minimum inhibitory concentrations (MICs) were determined on baseline isolates. Multivariate logistic regression and the assumption-free multivariate adaptive regression splines (MARS) were used to identify clinical and PK/PD predictors of 2-month culture conversion. Potential PK/PD predictors included 0- to 24-hour area under the curve (AUC0-24), maximum concentration (Cmax), AUC0-24/MIC, Cmax/MIC, and percentage of time that concentrations persisted above the MIC (%TMIC). RESULTS: Twenty-six percent of patients had Cmax of rifampicin <8 mg/L, pyrazinamide <35 mg/L, and isoniazid <3 mg/L. No relationship was found between PK exposures and 2-month culture conversion using multivariate logistic regression after adjusting for MIC. However, MARS identified negative interactions between isoniazid Cmax and rifampicin Cmax/MIC ratio on 2-month culture conversion. If isoniazid Cmax was <4.6 mg/L and rifampicin Cmax/MIC <28, the isoniazid concentration had an antagonistic effect on culture conversion. For patients with isoniazid Cmax >4.6 mg/L, higher isoniazid exposures were associated with improved rates of culture conversion. CONCLUSIONS: PK/PD analyses using MARS identified isoniazid Cmax and rifampicin Cmax/MIC thresholds below which there is concentration-dependent antagonism that reduces 2-month sputum culture conversion.

Optimizing treatment outcome of first-line anti-tuberculosis drugs: the role of therapeutic drug monitoring.

INTRODUCTION: Tuberculosis (TB) remains one of the world's deadliest communicable diseases. Although cure rates of the standard four-drug (rifampicin, isoniazid, pyrazinamide, ethambutol) treatment schedule can be as high as 95-98 % under clinical trial conditions, success rates may be much lower in less well resourced countries. Unsuccessful treatment with these first-line anti-TB drugs may lead to the development of multidrug resistant and extensively drug resistant TB. The intrinsic interindividual variability in the pharmacokinetics (PK) of the first-line anti-TB drugs is further exacerbated by co-morbidities such as HIV infection and diabetes. METHODS: Therapeutic drug monitoring has been proposed in an attempt to optimize treatment outcome and reduce the development of drug resistance. Several studies have shown that maximum plasma concentrations (C max), especially of rifampicin and isoniazid, are well below the proposed target C max concentrations in a substantial fraction of patients being treated with the standard four-drug treatment schedule, even though treatment's success rate in these studies was typically at least 85 %. DISCUSSION: The proposed target C max concentrations are based on the concentrations of these agents achieved in healthy volunteers and patients receiving the standard doses. Estimation of C max based on one or two sampling times may not have the necessary accuracy since absorption rate, especially for rifampicin, may be highly variable. In addition, minimum inhibitory concentration (MIC) variability should be taken into account to set clinically meaningful susceptibility breakpoints. Clearly, there is a need to better define the key target PK and pharmacodynamic (PD) parameters for therapeutic drug monitoring (TDM) of the first-line anti-TB drugs to be efficacious, C max (or area under the curve (AUC)) and C max/MIC (or AUC/MIC). CONCLUSION: Although TDM of first-line anti-TB drugs has been successfully used in a limited number of specialized centers to improve treatment outcome in slow responders, a better characterization of the target PK and/or PK/PD parameters is in our opinion necessary to make it cost-effective.

Monoammonium glycyrrhizinate protects rifampicin- and isoniazid-induced hepatotoxicity via regulating the expression of transporter Mrp2, Ntcp, and Oatp1a4 in liver.

CONTEXT: Drug-induced liver injury (DILI) is associated with altering expression of hepatobiliary membrane transporters. Monoammonium glycyrrhizin (MAG) is commonly used for hepatic protection and may have a correlation with the inhibition effect of multidrug resistance-associated protein 2 (Mrp2). OBJECTIVE: This study evaluates the dynamic protective effect of MAG on rifampicin (RIF)- and isoniazid (INH)-induced hepatotoxicity in rats. MATERIALS AND METHODS: Male Wistar rats were randomly divided into four groups of 15 rats. Liver injury was induced by co-treatment with RIF (60 mg/kg) and INH (60 mg/kg) by gavage administration; MAG was orally pretreated at the doses of 45 or 90 mg/kg 3 h before RIF and INH. Rats in each group were sacrificed at 7, 14, and 21 d time points after drug administration. RESULTS: Liver function, histopathological analysis, and oxidative stress factors were significantly altered in each group. The expression of Mrp2 was significantly increased 230, 760, and 990% at 7, 14, and 21 time points, respectively, in RIF- and INH-treated rats. Compared with the RIF and INH groups, Mrp2 was reduced and Ntcp was significantly elevated by 180, 140, and 160% in the MAG high-dose group at the three time points, respectively. The immunoreaction intensity of Oatp1a4 was increased 170, 190, and 370% in the MAG low-dose group and 160, 290, and 420% in the MAG high-dose group at the three time points, respectively, compared with the RIF and INH groups. DISCUSSION AND CONCLUSION: These results indicated that MAG has a protective effects against RIF- and INH-induced hepatotoxicity. The underlying mechanism may have correlation with its effect on regulating the expression of hepatobiliary membrane transporters.

Pharmacokinetics of Rifampin, Isoniazid, Pyrazinamide, and Ethambutol in Infants Dosed According to Revised WHO-Recommended Treatment Guidelines.

There are limited pharmacokinetic data for use of the first-line antituberculosis drugs during infancy (<12 months of age), when drug disposition may differ. Intensive pharmacokinetic sampling was performed in infants routinely receiving antituberculosis treatment, including rifampin, isoniazid, pyrazinamide, and ethambutol, using World Health Organization-recommended doses. Regulatory-approved single-drug formulations, including two rifampin suspensions, were used on the sampling day. Assays were conducted using liquid chromatography-mass spectrometry; pharmacokinetic parameters were generated using noncompartmental analysis. Thirty-nine infants were studied; 14 (36%) had culture-confirmed tuberculosis. Fifteen (38%) were premature (<37 weeks gestation); 5 (13%) were HIV infected. The mean corrected age and weight were 6.6 months and 6.45 kg, respectively. The mean maximum plasma concentrations (Cmax) for rifampin, isoniazid, pyrazinamide, and ethambutol were 2.9, 7.9, 41.9, and 1.3 µg/ml, respectively (current recommended adult target concentrations: 8 to 24, 3 to 6, 20 to 50, and 2 to 6 µg/ml, respectively), and the mean areas under the concentration-time curves from 0 to 8 h (AUC0-8) were 12.1, 24.7, 239.4, and 5.1 µg · h/ml, respectively. After adjusting for age and weight, rifampin exposures for the two formulations used differed inCmax(geometric mean ratio [GMR],2.55; 95% confidence interval [CI], 1.47 to 4.41;P= 0.001) and AUC0-8(GMR, 2.52; 95% CI, 1.34 to 4.73;P= 0.005). HIV status was associated with lower pyrazinamideCmax(GMR, 0.85; 95% CI, 0.75 to 0.96;P= 0.013) and AUC0-8(GMR, 0.79; 95% CI, 0.69 to 0.90;P< 0.001) values. No other important differences were observed due to age, weight, prematurity, ethnicity, or gender. In summary, isoniazid and pyrazinamide concentrations in infants compared well with proposed adult target concentrations; ethambutol concentrations were lower but similar to previously reported pediatric studies. The low rifampin exposures require further investigation. (This study has been registered at ClinicalTrials.gov under registration no. NCT01637558.).

St. John's wort treatment in women bears risks beyond pharmacokinetic drug interactions.

We analyzed adverse events in a clinical phase I trial to assess dose-dependent metabolic effects of St. John's wort co-administered with rifampicin in 12 healthy volunteers. Within 3-6 days after increasing the St. John's wort dose from 300 to 600 mg TID, five of six female participants developed ambient temperature-dependent allodynia and paresthesia in sun-exposed areas (back of the hands and perioral and nasal area). Aggravation of symptoms resulted in persistence of paresthesia and phototoxic erythrodermia. None of the male participants showed any of these effects. Gender, duration of treatment, dose, and solar exposure seem to be extrinsic and host factors facilitating St. John's wort-induced neuropathy. The risk to develop this adverse effect is almost exclusively present in women.

Correlations Between the Hollow Fiber Model of Tuberculosis and Therapeutic Events in Tuberculosis Patients: Learn and Confirm.

BACKGROUND: The hollow fiber system model of tuberculosis (HFS-TB) is designed to perform pharmacokinetics/pharmacodynamics (PK/PD) experiments, and hence the design of optimal doses and dose schedules for the treatment of tuberculosis. To determine if this model is useful for deriving PK/PD data relevant to clinical outcomes, we compared its quantitative output to that from clinical trials. METHODS: We performed a PubMed search to identify clinical studies performed with antituberculosis therapy in which PK/PD data and/or parameters were documented or a dose-scheduling study design was employed. The search period was from January 1943 to December 2012. All clinical studies were published prior to HFS-TB experiments. Bias minimization was done according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses. Clinical publications were scored for quality of evidence, with 1 as the highest score (randomized controlled trials or meta-analyses of such studies), and 4 as the lowest score. RESULTS: We identified 17 studies that examined the same parameters as in 8 HFS-TB studies. Fifteen of 17 studies had a quality-of-evidence score of 1. The sterilizing and bactericidal effect rates for isoniazid, rifampin, pyrazinamide, and ethambutol were the same in the HFS-TB as in patients. Time to emergence of resistance for monotherapy was the same as in patients. The PK/PD indices associated with efficacy were the same in HFS-TB as in patients for all drugs examined. CONCLUSIONS: The HFS-TB model is highly accurate at identifying optimal drug exposures, doses, and dosing schedules for use in the clinic.

Computational pharmacokinetics/pharmacodynamics of rifampin in a mouse tuberculosis infection model.

One critical approach to preclinical evaluation of anti-tuberculosis (anti-TB) drugs is the study of correlations between drug exposure and efficacy in animal TB infection models. While such pharmacokinetic/pharmacodynamic (PK/PD) studies are useful for the identification of optimal clinical dosing regimens, they are resource intensive and are not routinely performed. A mathematical model capable of simulating the PK/PD properties of drug therapy for experimental TB offers a way to mitigate some of the practical obstacles to determining the PK/PD index that best correlates with efficacy. Here, we present a preliminary physiologically based PK/PD model of rifampin therapy in a mouse TB infection model. The computational framework integrates whole-body rifampin PKs, cell population dynamics for the host immune response to Mycobacterium tuberculosis infection, drug-bacteria interactions, and a Bayesian method for parameter estimation. As an initial application, we calibrated the model to a set of available rifampin PK/PD data and simulated a separate dose fractionation experiment for bacterial killing kinetics in the lungs of TB-infected mice. The simulation results qualitatively agreed with the experimentally observed PK/PD correlations, including the identification of area under the concentration-time curve as best correlating with efficacy. This single-drug framework is aimed toward extension to multiple anti-TB drugs in order to facilitate development of optimal combination regimens.

Impact of nonlinear interactions of pharmacokinetics and MICs on sputum bacillary kill rates as a marker of sterilizing effect in tuberculosis.

The relationships between antituberculosis drug exposure and treatment effects on humans receiving multidrug therapy are complex and nonlinear. In patients on treatment, an analysis of the rate of decline in the sputum bacillary burden reveals two slopes. The first is the α-slope, which is thought to reflect bactericidal effect, followed by a ß-slope, which is thought to reflect sterilizing activity. We sought to characterize the effects of standard first-line treatment on sterilizing activity. Fifty-four patients receiving combination therapy for pulmonary tuberculosis in a clinical trial had drug concentrations measured and Mycobacterium tuberculosis isolates available for MIC identification. Sputum sample cultures were performed at baseline and weekly for 8 weeks. A time-to-event model based on the days to positivity in the liquid cultures was used to estimate the ß-slope. The pharmacokinetic parameters of rifampin, isoniazid, ethambutol, and pyrazinamide were determined for each patient. Multivariate adaptive regression splines analyses, which simultaneously perform linear and nonlinear analyses, were used to identify the relationships between the predictors and the ß-slope. The potential predictors examined included HIV status, lung cavitation, 24-h area under the concentration-time curve (AUC), peak drug concentration (Cmax), AUC/MIC ratio, Cmax/MIC ratio, and the time that that concentration persisted above MIC. A rifampin Cmax of >8.2 mg/liter and a pyrazinamide AUC/MIC of >11.3 were key predictors of the ß-slope and interacted positively to increase the ß-slope. In patients with a rifampin AUC of <35.4 mg · h/liter, an increase in the pyrazinamide AUC/MIC and/or ethambutol Cmax/MIC increased the ß-slope, while increasing isoniazid Cmax decreased it, suggesting isoniazid antagonism. Antibiotic concentrations and MICs interact in a nonlinear fashion as the main drivers of a sterilizing effect. The results suggest that faster speeds of sterilizing effect might be achieved by omitting isoniazid and by increasing rifampin, pyrazinamide, and ethambutol exposures. However, isoniazid and ethambutol exposures may only be of importance when rifampin exposure is low. These findings need confirmation in larger studies. (This study has been registered at controlled-trials.com under registration no. ISRCTN80852505.).

Formulation of novel sustained release rifampicin-loaded solid lipid microparticles based on structured lipid matrices from Moringa oleifera.

OBJECTIVES: To formulate sustained release rifampicin-loaded solid lipid microparticles (SLMs) using structured lipid matrices based on Moringa oil (MO) and Phospholipon 90G (P90G). METHODS: Rifampicin-loaded and unloaded SLMs were formulated by melt homogenization and characterized in terms of particle morphology and size, percentage drug content (PDC), pH stability, stability in simulated gastric fluid (SGF, pH 1.2), minimum inhibitory concentration (MIC) and in vitro release. In vivo release was studied in Wistar rats. RESULTS: Rifampicin-loaded SLMs had particle size range of 32.50 ± 2.10 to 34.0 ± 8.40 µm, highest PDC of 87.6% and showed stable pH. SLMs had good sustained release properties with about 77.1% release at 12 h in phosphate buffer (pH 6.8) and 80.3% drug release at 12 h in simulated intestinal fluid (SIF, pH 7.4). SLMs exhibited 48.51% degradation of rifampicin in SGF at 3 h, while rifampicin pure sample had 95.5% degradation. Formulations exhibited MIC range of 0.781 to 1.562, 31.25 to 62.5 and 6.25 to 12.5 µg/ml against Salmonella typhi, Escherichia coli, and Bacillus subtilis respectively and had higher in vivo absorption than the reference rifampicin (p < 0.05). CONCLUSION: Rifampicin-loaded SLMs could be used once daily for the treatment tuberculosis.

Population pharmacokinetics of rifampin in the treatment of Mycobacterium tuberculosis in Asian elephants.

The objective of this study was to develop a population pharmacokinetic model for rifampin in elephants. Rifampin concentration data from three sources were pooled to provide a total of 233 oral concentrations from 37 Asian elephants. The population pharmacokinetic models were created using Monolix (version 4.2). Simulations were conducted using ModelRisk. We examined the influence of age, food, sex, and weight as model covariates. We further optimized the dosing of rifampin based upon simulations using the population pharmacokinetic model. Rifampin pharmacokinetics were best described by a one-compartment open model including first-order absorption with a lag time and first-order elimination. Body weight was a significant covariate for volume of distribution, and food intake was a significant covariate for lag time. The median Cmax of 6.07 µg/mL was below the target range of 8-24 µg/mL. Monte Carlo simulations predicted the highest treatable MIC of 0.25 µg/mL with the current initial dosing recommendation of 10 mg/kg, based upon a previously published target AUC0-24/MIC > 271 (fAUC > 41). Simulations from the population model indicate that the current dose of 10 mg/kg may be adequate for MICs up to 0.25 µg/mL. While the targeted AUC/MIC may be adequate for most MICs, the median Cmax for all elephants is below the human and elephant targeted ranges.