Can the duration of tuberculosis treatment be shortened with higher dosages of rifampicin?

A review of recent advances in anti-tubercular drug development

Tuberculosis is a global threat but in particular affects people from developing countries. It is thought that nearly a third of the population of the world live with its causative bacteria in a dormant form. Although tuberculosis is a curable disease, the chances of cure become slim as the disease becomes multidrug-resistant and the situation gets even worse as the disease becomes extensively drug-resistant. After approximately 5 decades without any new TB drug in the pipeline, there has been some good news in the recent years with the discovery of new drugs such as bedaquiline and delamanid as well as the discovery of new classes of anti-tubercular drugs. Some old drugs such as clofazimine, linezolid and many others which were not previously indicated for tuberculosis have been also repurposed for tuberculosis and they are performing well.

Considerations in preparing for clinical studies of inhaled rifampicin to enhance tuberculosis treatment

Drug delivery via the inhaled route has advantages for treating local and systemic diseases. Pulmonary drug delivery may have potential in treating tuberculosis (TB), which is mainly localised in the lung (pulmonary tuberculosis ∼75%) while also affecting other organs (extra-pulmonary tuberculosis). Currently, rifampicin, a first-line anti-tubercular drug, is given orally and the maximum daily oral dose is the lesser of 10 mg/kg or 600 mg. Since only a small fraction of this dose is available in the lung, concentrations may frequently fail to reach bactericidal levels, and therefore, contribute to the development of multi-drug resistant pulmonary TB. Pulmonary delivery of rifampicin, either alone or in addition to the standard oral dose, has the potential to achieve a high concentration of rifampicin in the lung at a relatively low administered dose that is sufficient to kill bacteria and reduce the development of drug resistance. As yet, no clinical study in humans has reported the pharmacokinetics or the efficacy of pulmonary delivery of rifampicin for TB. This review discusses the opportunities and challenges of rifampicin delivery via the inhaled route and important considerations for future clinical studies on high dose inhaled rifampicin are illustrated.

A High-throughput Compatible Assay to Evaluate Drug Efficacy against Macrophage Passaged Mycobacterium tuberculosis

The early drug development process for anti-tuberculosis drugs is hindered by the inefficient translation of compounds with in vitro activity to effectiveness in the clinical setting. This is likely due to a lack of consideration for the physiologically relevant cellular penetration barriers that exist in the infected host. We recently established an alternative infection model that generates large macrophage aggregate structures containing densely packed M. tuberculosis (Mtb) at its core, which was suitable for drug susceptibility testing. This infection model is inexpensive, rapid, and most importantly BSL-2 compatible. Here, we describe the experimental procedures to generate Mtb/macrophage aggregate structures that would produce macrophage-passaged Mtb for drug susceptibility testing. In particular, we demonstrate how this infection system could be directly adapted to the 96-well plate format showing throughput capability for the screening of compound libraries against Mtb. Overall, this assay is a valuable addition to the currently available Mtb drug discovery toolbox due to its simplicity, cost effectiveness, and scalability.

Statin adjunctive therapy shortens the duration of TB treatment in mice

BACKGROUND

The repurposing of existing agents may accelerate TB drug development. Recently, we reported that the lipid-lowering drug simvastatin, when added to the first-line antitubercular regimen, reduces the lung bacillary burden in chronically infected mice.

OBJECTIVES

We investigated whether the addition of simvastatin to the first-line regimen (isoniazid/rifampicin/pyrazinamide) shortens the duration of curative TB treatment in mice.

METHODS

Mycobacterium tuberculosis-infected THP-1 cells were exposed to simvastatin to determine the effect of statins on the activity of first-line anti-TB drug activity and intracellular rifampicin concentration. Single-dose and steady-state pharmacokinetic studies guided optimized simvastatin dosing in vivo. BALB/c mice were aerosol-infected with M. tuberculosis H37Rv and drug treatment was initiated 6 weeks post-infection. Separate groups of mice received standard TB treatment with or without simvastatin. Relapse rates were assessed 3 months after discontinuation of each treatment regimen. MALDI-MS imaging was used to image the cholesterol content of mouse lung lesions.

RESULTS

Simvastatin significantly enhanced the bactericidal activity of first-line drugs against intracellular M. tuberculosis without altering intracellular rifampicin concentrations. Adjunctive treatment with 60 mg/kg simvastatin shortened the time required to achieve culture-negative lungs from 4.5 to 3.5 months. Following 2.5, 3.5 and 4.5 months of treatment, relapse rates were 100%, 50% and 0%, respectively, in the control group and 50% (P = 0.03), 20% and 0%, respectively, in the statin group. Simvastatin did not alter plasma or lung lesion cholesterol levels.

CONCLUSIONS

Statins are attractive candidates for host-directed, adjunctive TB therapy. Further preclinical studies are needed to define the optimal statin and dosing.