IMR participated in the planning, execution, analysis, and writing of the final manuscript. MZ and KNW participated in the treatment of animals and the assessment of treatment efficacy. CAP provided HPLC assays to measure the drug concentrations and performed simulations of the data. ST participated in the execution of the pharmacokinetic experiments. AAV and WRB provided guidance as well as editorial assistance. REC participated in the planning, analysis, and review of the final manuscript. JHG and ELN participated in the planning, supervision, analysis, and writing that led to the present manuscript. IMR, MZ, KNW, CAP, ST, AAV, WRB, REC, JHG, and ELN saw and approved the final version of the manuscript.
WRB: Pending grant from Schering Plough, which markets moxifloxacin in the United States of America. Past grant from Bayer, which manufactures moxifloxacin. Past advisor for Schering Plough. Past grant from Hoechst Marion Roussel (now Sanofi Aventis), producer of rifapentine. Multiple other past and present pharmaceutical grants from companies whose drugs are not involved in this study. Multiple other past and present pharmaceutical advisory roles for companies whose drugs are not involved in this study. REC: Donations of drugs for federally funded research trials from Bayer (moxifloxacin) and Aventis (rifapentine). Honoraria (US$1,200) from Bayer to chair an independent Data Safety Monitoring Board for an experimental drug for HIV infection. For all other authors, no conflicts of interest are declared.
Availability of an ultra-short-course drug regimen capable of curing patients with tuberculosis in 2 to 3 mo would significantly improve global control efforts. Because immediate prospects for novel treatment-shortening drugs remain uncertain, we examined whether better use of existing drugs could shorten the duration of treatment. Rifapentine is a long-lived rifamycin derivative currently recommended only in once-weekly continuation-phase regimens. Moxifloxacin is an 8-methoxyfluoroquinolone currently used in second-line regimens.
Using a well-established mouse model with a high bacterial burden and human-equivalent drug dosing, we compared the efficacy of rifapentine- and moxifloxacin-containing regimens with that of the standard daily short-course regimen based on rifampin, isoniazid, and pyrazinamide. Bactericidal activity was assessed by lung colony-forming unit counts, and sterilizing activity was assessed by the proportion of mice with culture-positive relapse after 2, 3, 4, and 6 mo of treatment. Here, we demonstrate that replacing rifampin with rifapentine and isoniazid with moxifloxacin dramatically increased the activity of the standard daily regimen. After just 2 mo of treatment, mice receiving rifapentine- and moxifloxacin-containing regimens were found to have negative lung cultures, while those given the standard regimen still harbored 3.17 log10 colony-forming units in the lungs (
Rifapentine should no longer be viewed solely as a rifamycin for once-weekly administration. Our results suggest that treatment regimens based on daily and thrice-weekly administration of rifapentine and moxifloxacin may permit shortening the current 6 mo duration of treatment to 3 mo or less. Such regimens warrant urgent clinical investigation.
Eric Nuermberger and colleagues found that after two months of treatment, mice with lung cultures positive for tuberculosis that received daily doses of rifapentine- and moxifloxacin-containing regimens converted to negative lung cultures. This finding could make possible the development of shorter treatment regimens for humans.
Every year, nearly 9 million people develop tuberculosis—a bacterial infection most commonly of the lungs—and about 2 million people die from the disease. Tuberculosis is caused by
Unfortunately, many patients fail to complete this treatment because it is long and complicated and because the drugs may have unpleasant side effects. Poor adherence to treatment contributes to the emergence of drug resistance and means that people stay infectious for longer and are more likely to have relapses. Consequently, it is hampering global efforts to control tuberculosis. A shorter course of treatment might improve matters, but many researchers believe that this will require the development of new drugs and, although there are several promising candidates, it will be several years before they can be used in patients. In this study, therefore, the researchers asked whether better use of existing drugs could shorten treatment times. In particular, they studied tuberculosis in animals to investigate whether a long-lived rifampin-like drug called rifapentine combined with moxifloxacin (an alternative to isoniazid) might shorten treatment times.
The researchers used several different courses (“regimens”) of treatment containing rifapentine, moxifloxacin, and pyrazinamide, and the standard daily short-course regimen containing rifampin, isoniazid, and pyrazinamide to treat mice infected with
These findings provide the first evidence that replacing rifampin with rifapentine might halve the length of therapy needed to cure tuberculosis. They also indicate that it might be possible to give the drugs thrice-weekly rather than daily as in the current therapy. The World Health Organization recommends that all tuberculosis treatment is supervised (so-called directly observed therapy) to ensure treatment adherence, so a regimen that requires only three doses a week for 3 mo would greatly reduce the resources needed to treat tuberculosis as well as potentially improving treatment adherence. However, it should be emphasized that the current study is experimental, and there may be important differences between how mice and people respond to the proposed drug regimens, both in terms of cure rates and side effects. Nevertheless, these results strongly suggest that the safety, tolerability, and efficacy of tuberculosis treatment regimens containing rifapentine and pyrazinamide, combined with either moxifloxacin or isoniazid, should be evaluated in people as soon as possible.
Please access these Web sites via the online version of this summary at
The MedlinePlus encyclopedia contains a page on
The US National Institute of Allergy and Infectious Diseases provides information on all aspects of
The US Centers for Disease Control and Prevention provide several fact sheets and other information resources about
The World Health Organization provides a 2007 report on
The development of simplified treatment regimens is a major priority of the Global Plan to Stop TB [
It is widely believed that shortening the duration of TB therapy will require the development of new drugs with novel mechanisms of action [
Rifampin is recognized as the most important sterilizing drug in the modern short-course regimen. However, rifampin has a relatively short half-life of 2–4 h [
Low rifamycin drug exposure might explain the suboptimal efficacy of once-weekly rifapentine-containing regimens, particularly in the light of rifapentine's high protein binding [
Moxifloxacin (M) was kindly provided by Bayer Pharmaceuticals, isoniazid (H) and rifampin (R) were purchased from Sigma, and pyrazinamide (Z) was purchased from Fisher Scientific International. All drugs were either dissolved or suspended in water prior to oral gavage. Rifapentine (P) tablets, donated by Sanofi-Aventis, were ground into a fine powder, suspended in water, and briefly sonicated before gavage. Drug solutions were prepared weekly and stored at 4 °C.
Six-week-old BALB/c mice (Charles River) were aerosol infected with
Treatment began 15 d after infection (on D0) in the first chemotherapeutic study (
Scheme of Chemotherapy Experiment
CFU counts at treatment initiation (D0) and (A) after 1 mo, (B) after 2 mo, and (C) after 3 mo of treatment. Data are presented as means and standard error (error bars) (
At the start of treatment (D0), mice were block-randomized (by infection run) into eight groups (
In the second chemotherapeutic study (
Treatment began when the bacillary burden reached 7.45 ± 0.03 log10 CFU per lung. After 10 wk of treatment and 3 mo of follow-up, the proportion of mice that were lung culture–positive was 100% and 53% for the R-containing regimens (R10HZ and R10MZ, respectively) and only 13% and 0% for the P-containing regimens (P10HZ and P10MZ, respectively) (data not shown in Figure). H, isoniazid; M, moxifloxacin; Z, pyrazinamide; R, rifampin; P, rifapentine.
Treatment efficacy was assessed on the bases of lung colony-forming unit (CFU) counts and the proportion of mice with culture-positive relapse after treatment completion. To monitor the bacterial multiplication and establish baseline CFU counts prior to treatment, untreated mice were humanely killed the day after aerosol infection, with others killed 14 d later (D0), at the initiation of treatment. Subsequently, mice from all treatment groups were killed during treatment to assess bactericidal activity. Lungs were removed under aseptic conditions, placed in phosphate-buffered saline, homogenized, and plated on 7H11 agar enriched with 10% oleic acid-albumin-dextrose-catalase and supplemented with cycloheximide (10 μg/ml), carbenicillin (50 μg/ml), polymyxin B (25 μg/ml), and trimethoprim (20 μg/ml) to prevent contamination. Plates were incubated for 28 d at 37 °C in a 5% CO2 environment before CFU counts were determined.
The proportion of culture-positive mice was determined by humanely killing a cohort of mice 3 mo after the completion of treatment. Mice were considered to be culture-positive if ≥1 CFU was identified after plating the entire lung homogenate. In chemotherapy study 1 (
Rifamycin pharmacokinetics were determined in uninfected female Swiss Webster mice after oral gavage with single doses of R10, P7.5, P10, P15, and P20. Drug concentrations in mouse plasma were determined by validated HPLC assays. Single-dose serum-concentration time curves were determined using non-compartmental techniques (WinNonLin Software). Steady-state pharmacokinetics assuming no autoinduction were simulated using nonparametric superposition, followed by simulation using a one-compartment model with first-order elimination. Parameter estimates (absorption rate constant, volume of distribution, and elimination rate constant) were adjusted to match the median single-dose serum-concentration time curve measured in mice, followed by simulation of various doses and frequencies of administration. Simulated pharmacokinetic parameter estimates were compared to actual published and unpublished steady-state concentrations determined for selected twice-daily and daily (5/7) regimens and showed excellent concordance [
CFU counts were log10 transformed before analysis and expressed as CFU log10 ± standard error. Mean CFU counts were compared using one-way ANOVA followed by Dunnett's multiple comparison test (Stata 8.2). The proportions of mice relapsing after completing treatment were compared using Fisher's Exact test. Bonferroni's procedure was used to adjust the type I error rate for multiple comparisons.
In the first chemotherapeutic study, mice were aerosol infected with
At completion of the first month of treatment, all intermittent and daily PMZ regimens had significantly greater bactericidal activity than the standard daily (5/7) RHZ regimen (
After 2 mo of treatment, all mice receiving a PMZ-based regimen had no detectable CFU, with the exception of two of the five mice treated with twice-weekly P15MZ, which harbored 1 and 5 CFU per lung, respectively (
To further investigate the activity of the P10MZ (5/7) regimen, we determined the individual contributions of P and M on the regimen's overall activity in a second chemotherapeutic study (
To assess the duration of treatment required to achieve stable cure, we determined the proportion of mice with culture-positive relapse after the end of treatment (
Culture-Positive Relapse Rates after Treatment with the Standard Daily Regimen (RHZ) and with Intermittent and Daily PMZ Regimens in
Relapse was not assessed in mice treated with the standard control regimen, RHZ (5/7), until after 4 and 6 mo of treatment, where 90% and 0% of mice relapsed, respectively. Overall, these findings demonstrate that the duration of treatment required to achieve 0% relapse was decreased by at least 3 mo for the PMZ regimens administered daily or thrice-weekly as compared to the duration required with the standard daily regimen.
In the second chemotherapeutic study, we determined the proportion of mice with positive cultures 3 mo after completing 10 wk of treatment (
Finally, in order to confirm the increased rifamycin exposure associated with P administration, we compared the single-dose pharmacokinetic parameters (
Mice were administered a single dose of 7.5, 10, 15, and 20 mg/kg of rifapentine or 10 mg/kg of rifampin. P, rifapentine; R, rifampin.
Steady-State Pharmacokinetic and Pharmacodynamic Parameters for Rifapentine and Rifampin in Mice
Mice were treated with (A) twice-weekly (2/7) rifapentine 15 mg/kg (dashed line) and 20 mg/kg (solid line); (B) thrice-weekly (3/7) rifapentine 15 mg/kg; (C) daily (5/7) rifapentine 7.5 mg/kg (dashed line) and 10 mg/kg (solid line); (D) daily (7/7) rifapentine 10 mg/kg; and (e) daily (5/7) rifampin 10 mg/kg. Rifamycin concentrations are expressed in terms of free drug (2.5% and 17.5% free drug for rifapentine and rifampin, respectively). The free rifamycin concentration is below the MIC when the curve falls below the solid horizontal line. Pharmacodynamic parameter estimates are shown in
We set out to determine whether two currently registered drugs, rifapentine and moxifloxacin, could be used more effectively to improve the treatment of TB. Our results demonstrate that the combination of increasing rifamycin drug exposure by replacing rifampin with rifapentine and replacing isoniazid with moxifloxacin in the standard 6-mo daily treatment regimen may radically shorten the duration of therapy necessary to cure patients of TB. Treatment with P7.5MZ and P10MZ 5 d/wk (5/7) eliminated
The long serum half-lives of P and M also might enable treatment-shortening regimens to be administered intermittently as opposed to daily, thus further reducing the resources necessary to administer supervised treatment [
The finding that all PMZ regimens were more active than the standard daily R10HZ regimen may be explained largely by the greater rifamycin exposure obtained by substituting P for R, as a consequence of the former's longer elimination half-life. In support of this premise, we found that the AUC168 h/MIC and the percentage of time above MIC were substantially greater for P-based regimens compared to the R-based regimen. Specifically, the free drug AUC168 h/MIC values ranged from 26% to 180% greater for P-based regimens, as compared to daily R (10 mg/kg), and free drug concentrations exceeded the MIC for at least 90% of the dosing interval in each P-based regimen, but for only 60% of the time in the daily R regimen (
The substitution of M for H also contributes to the enhanced activity of PMZ regimens over RHZ, as demonstrated in our second chemotherapeutic study (
Our results with daily and intermittent P-based regimens are especially encouraging in the light of recent clinical findings that intermittent treatment with RHZ is less active than the same treatment administered daily [
Several caveats must be considered when extrapolating these results from the murine model to the treatment of humans. First and foremost is the reliability with which the murine model predicts the outcomes of TB chemotherapy in humans. When care is taken to create a bacillary burden that is representative of that found in human cavitary TB and to administer drugs at human-equivalent doses, the mouse model has a strong track record of predicting the duration of treatment necessary to attain acceptable cure rates in human TB with various regimens, including RHZ [
A second caveat is that the safety and tolerability of the PMZ regimens studied here have yet to be investigated in humans. P has been well tolerated when administered at 10 mg/kg twice-weekly or at 15 and 20 mg/kg once-weekly for 2 mo or more [
In conclusion, we have used a well-established murine model to reevaluate the potential contribution of P to the treatment of TB. This study has identified novel regimens that are dramatically more effective than the standard short-course RHZ regimen. We believe their greater efficacy is due primarily to the greater rifamycin exposure obtained when P is administered more frequently than once-weekly. A more modest beneficial effect of replacing H with M was also observed. Because of the prolonged elimination half-life of P, both intermittent and daily P-based regimens may have the potential to shorten the duration of treatment, perhaps to 3 mo or less. These results underscore the value of understanding antimicrobial pharmacodynamics for new and existing TB drugs in order to maximize their potential contribution and support the urgent evaluation of the safety, tolerability, and efficacy of P-based regimens for the treatment of TB.
area under the serum concentration versus time curve divided by the minimum inhibitory concentration
colony-forming unit
maximum serum concentration
ethambutol
isoniazid
moxifloxacin
minimum inhibitory concentration
rifapentine
rifapentine plus moxifloxacin plus pyrazinamide
rifampin
rifampin plus isoniazid plus pyrazinamide
tuberculosis
pyrazinamide