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.
Methods and Findings
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 (p < 0.01). No relapse was observed after just 3 mo of treatment with daily and thrice-weekly administered rifapentine- and moxifloxacin-containing regimens, whereas the standard daily regimen required 6 mo to prevent relapse in all mice.
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 Mycobacterium tuberculosis, bacteria that are spread in airborne droplets when people with active tuberculosis sneeze or cough. Most infected people never become ill—their immune system successfully contains the infection. However, the bacteria remain dormant within the body and can cause disease years later if host immunity declines. Active tuberculosis can be cured by taking several antibiotics daily (for tuberculosis treatments, daily may mean five or seven times a week) for at least 6 mo. Combinations of drugs are needed to prevent the bacteria from developing resistance to the treatment, but also because of the complex biology of M. tuberculosis. During active tuberculosis, there are rapidly multiplying bacteria in the lungs but also less rapidly multiplying and near-dormant bacteria elsewhere in the body. Effective treatments contain a “bactericidal” drug such as isoniazid to kill the actively multiplying bacteria, a drug to kill the less actively multiplying bugs (for example, pyrazinamide), and a sterilizing drug (the most potent of which is rifampin) to kill the near-dormant bacteria and thus prevent the disease from recurring.
Why Was This Study Done?
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.
What Did the Researchers Do and Find?
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 M. tuberculosis. For each regimen, they measured its bactericidal activity by counting how many bacterial colonies could be grown from the lungs of the mice at specific times during the treatment, and its sterilizing activity by assessing the proportion of mice with any live bacteria in their lungs (a culture-positive relapse) after treatment completion. After 2 mo of treatment, the mice receiving the rifapentine- and moxifloxacin-containing regimens had negative lung cultures, a point not reached with the standard regimen until after 4 mo of treatment. Three months of treatment with daily or thrice-weekly rifapentine- and moxifloxacin-containing regimens was sufficient to prevent any culture-positive relapses, whereas the standard daily regimen had to be continued for 6 mo to achieve cure. Testing of additional drug combinations revealed that rifapentine is the most important drug in the new regimen and that simply replacing rifampin with rifapentine and retaining isoniazid also is sufficient to shorten the duration of therapy to 3 mo in this experimental model.
What Do These Findings Mean?
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 http://dx.doi.org/10.1371/journal.pmed.0040344.
The MedlinePlus encyclopedia contains a page on tuberculosis (in English and Spanish)
The US National Institute of Allergy and Infectious Diseases provides information on all aspects of tuberculosis
The US Centers for Disease Control and Prevention provide several fact sheets and other information resources about tuberculosis, including information for patients and caregivers about treatment adherence
The World Health Organization provides a 2007 report on global tuberculosis control (in English with key findings in French and Spanish), information on the Stop TB initiative, and a recent bulletin on tuberculosis treatment (in English with an abstract in French, Spanish, and Arabic)