Dual ß-Lactam Combinations Highly Active against Mycobacterium abscessus Complex In Vitro.

As a consequence of a growing population of immunocompromised individuals, including transplant recipients and cystic fibrosis patients, there has been a dramatic increase in chronic infections caused by Mycobacterium abscessus complex (MABC) strains that are usually recalcitrant to effective antibiotic therapy. The recent rise of macrolide resistance in MABC has further complicated this clinical dilemma, dramatizing the need for novel agents. The repurposing of current antibiotics is one rapid path from discovery to patient care. In this study, we have discovered that dual ß-lactams, and specifically the combination of ceftazidime with either ceftaroline or imipenem, are synergistic and have clinically relevant activities, with MIC50s of 0.25 (ceftaroline with 100 µg/ml ceftazidime) and 0.5 µg/ml (imipenem with 100 µg/ml ceftazidime) against clinical MABC isolates. Similar synergy was observed in time-kill studies against the M. abscessus ATCC 19977 strain using clinically achievable concentrations of either imipenem (4 µg/ml) or ceftaroline (2 µg/ml), as the addition of ceftazidime at concentrations of ≥50 µg/ml showed a persistent bactericidal effect over 5 days. Treatment of THP-1 human macrophages infected with three different M. abscessus clinical isolates supported the in vitro findings, as the combination of 100 µg/ml ceftazidime and 0.125 µg/ml ceftaroline or 100 µg/ml ceftazidime and 0.25 µg/ml imipenem dramatically reduced the CFU counts to near baseline levels of infection. This study's finding that there is synergy between certain ß-lactam combinations against M. abscessus infection provides optimism toward identifying an optimum dual ß-lactam treatment regimen.IMPORTANCE The emergence of chronic MABC infections among immunocompromised populations and their inherent and acquired resistance to effective antibiotic therapy have created clinical challenges in advancing patients for transplant surgery and treating those with disease. There is an urgent need for new treatment regimens, and the repurposing of existing antibiotics provides a rapid strategy to advance a laboratory finding to patient care. Our recent discoveries that dual ß-lactams, specifically the combination of ceftazidime with ceftaroline or ceftazidime with imipenem, have significant in vitro MIC values and kill curve activities and are effective against infected THP-1 human macrophages provide optimism for a dual ß-lactam treatment strategy against MABC infections. The unexpected synergistic activities reported in this study create a new path of discovery to repurpose the large family of ß-lactam drugs.

Long-acting formulations for the treatment of latent tuberculous infection: opportunities and challenges.

Long-acting/extended-release drug formulations have proved very successful in diverse areas of medicine, including contraception, psychiatry and, most recently, human immunodeficiency virus (HIV) disease. Though challenging, application of this technology to anti-tuberculosis treatment could have substantial impact. The duration of treatment required for all forms of tuberculosis (TB) put existing regimens at risk of failure because of early discontinuations and treatment loss to follow-up. Long-acting injections, for example, administered every month, could improve patient adherence and treatment outcomes. We review the state of the science for potential long-acting formulations of existing tuberculosis drugs, and propose a target product profile for new formulations to treat latent tuberculous infection (LTBI). The physicochemical properties of some anti-tuberculosis drugs make them unsuitable for long-acting formulation, but there are promising candidates that have been identified through modeling and simulation, as well as other novel agents and formulations in preclinical testing. An efficacious long-acting treatment for LTBI, particularly for those co-infected with HIV, and if coupled with a biomarker to target those at highest risk for disease progression, would be an important tool to accelerate progress towards TB elimination.

New Paradigm for Translational Modeling to Predict Long-term Tuberculosis Treatment Response.

Disappointing results of recent tuberculosis chemotherapy trials suggest that knowledge gained from preclinical investigations was not utilized to maximal effect. A mouse-to-human translational pharmacokinetics (PKs) - pharmacodynamics (PDs) model built on a rich mouse database may improve clinical trial outcome predictions. The model included Mycobacterium tuberculosis growth function in mice, adaptive immune response effect on bacterial growth, relationships among moxifloxacin, rifapentine, and rifampin concentrations accelerating bacterial death, clinical PK data, species-specific protein binding, drug-drug interactions, and patient-specific pathology. Simulations of recent trials testing 4-month regimens predicted 65% (95% confidence interval [CI], 55-74) relapse-free patients vs. 80% observed in the REMox-TB trial, and 79% (95% CI, 72-87) vs. 82% observed in the Rifaquin trial. Simulation of 6-month regimens predicted 97% (95% CI, 93-99) vs. 92% and 95% observed in 2RHZE/4RH control arms, and 100% predicted and observed in the 35 mg/kg rifampin arm of PanACEA MAMS. These results suggest that the model can inform regimen optimization and predict outcomes of ongoing trials.

Evolving strategies for dose optimization of linezolid for treatment of tuberculosis.

The role of linezolid (LZD) in the management of drug-resistant tuberculosis is evolving. Optimizing its usage to maximize efficacy while minimizing its toxicity requires greater understanding of the relationships between drug exposure and bacterial killing, resistance suppression and toxicity. Recent non-clinical and clinical studies provide some useful insights and are reviewed here. Because LZD toxicity is dose- and duration-dependent, and is driven by elevated trough concentrations and prolonged exposure to concentrations inhibiting mitochondrial protein synthesis, several innovative dosing strategies can be employed to optimize its usage. These strategies, which are not mutually exclusive, may include giving higher doses more intermittently, giving higher daily doses for shorter durations, and giving lower total durations. For example, one approach may involve daily doses of 900-1200 mg for the first 1-3 months of treatment, followed by intermittent (e.g., thrice-weekly) dosing of 1200 mg. Trials to evaluate regimens based on such strategies are required.

2011: the year in review. part I: tuberculosis.

IN THIS YEAR-IN-REVIEW ARTICLE, we summarizes 104 articles published on tuberculosis in the International Journal of Tuberculosis and Lung Disease from the January to the August issue in 201, and arbitrarily categorise them according to three subject areas: active TB, latent TB infection (LTBI),and operational research.

Safety and pharmacokinetics of escalating daily doses of the antituberculosis drug rifapentine in healthy volunteers.

Rifapentine (RP T) is an antituberculosis drug that may shorten treatment duration when substituted for rifampin (RI F).The maximal tolerated daily dose of RP T and its potential for cytochrome 3A4 induction and autoinduction at clinically relevant doses are unknown. In this phase I, dose-escalation study among healthy volunteers, daily doses as high asa prespecified maximum of 20 mg/kg/day were well tolerated. Steady-state RP T concentrations increased with dose from 5 to 15 mg/kg, but area under the plasma concentration­time curve (AU C0­24) and maximum concentration (Cmax)were similar in the 15- and 20-mg/kg cohorts. Although RP T pharmacokinetics (PK) appeared to be time-dependent,accumulation occurred with daily dosing. The mean AU C0­12 of oral midazolam (MDZ), a cytochrome 3A (CYP 3A) probe drug, was reduced by 93% with the coadministration of RPT and by 74% with the coadministration of RIF (P < 0.01).Changes in the oral clearance of MDZ did not vary by RP T dose. In conclusion, RP T was tolerated at doses as high as20 mg/kg/day, its PK were less than dose-proportional, and its CYP 3A induction was robust.

Promising antituberculosis activity of the oxazolidinone PNU-100480 relative to that of linezolid in a murine model.

Oxazolidinone antibiotics have activity against Mycobacterium tuberculosis. Linezolid, the only marketed oxazolidinone, has been used off-label in combination regimens to treat multidrug-resistant tuberculosis, but its precise contribution to the efficacy of such combinations is unclear. Another oxazolidinone, PNU-100480, has been demonstrated to have more potent activity in vitro and in a murine model of tuberculosis. In this study, we compared the pharmacokinetics and the antituberculosis activities of these two oxazolidinones over a range of doses and found that linezolid has limited activity at clinically relevant doses in the murine model compared to that of PNU-100480, which has potent bactericidal activity, even at lower drug exposures. These findings were unexpected, given the similar in vitro activities of PNU-100480, its major metabolites, and linezolid. Moreover, the incorporation of PNU-100480 dramatically improved the bactericidal activities of regimens containing current first-line antituberculosis drugs and moxifloxacin. For example, the addition of PNU-100480 (100 mg/kg of body weight/day) to the standard daily regimen of rifampin (rifampicin), isoniazid, and pyrazinamide resulted in an additional 2.0-log(10)-unit reduction in lung CFU counts during the first 2 months of treatment. The combination of PNU-100480, moxifloxacin, and pyrazinamide, which does not contain either rifampin or isoniazid, was also more active than rifampin, isoniazid, and pyrazinamide. These results suggest that PNU-100480 may have the potential to significantly shorten the duration of therapy for drug-susceptible as well as multidrug-resistant tuberculosis.

Pharmacokinetics and pharmacodynamics in the development of anti-tuberculosis drugs.

Optimization of dosing strategies and companion drugs prior to Phase III trials is currently a critical obstacle in the development of new anti-tuberculosis drugs. Pharmacokinetic-pharmacodynamic (PK-PD) methods have assumed an important role in improving the efficiency of this process across the pharmaceutical industry and in other areas of anti-infective therapy. Information gained using PK-PD methods from the earliest in vitro assessments right up to the end of Phase II development can underpin proof-of-concept and ensure that agents are fully pharmacologically optimized. Despite our limited understanding of the biology of bacillary elimination in vivo, such an approach has already provided key insights into these mechanisms and helped to identify the role of different drugs in therapy and assess their potential for progression to pivotal trials. While isoniazid appears historically to have been effectively exploited, human studies suggest that it does not play a key role in the sterilizing phase of treatment. Re-evaluation of the PK-PD of rifamycins by contrast suggests that there may be considerable scope for improving their activity by intensifying current dosing strategies. Various PK-PD analyses of the fluoroquinolone series demonstrate remarkable agreement concerning the ranking of their sterilizing activity, results which appear to be confirmed in recent human phase II studies. The pharmacological characteristics of completely new classes of drugs now entering clinical development suggest that experience with existing drugs, particularly EBA studies, should not prejudice evaluation of their pharmacodynamic activity which may differ qualitatively from that of many current agents. In conclusion, PK-PD analysis has a vital role to play in the rational development of new anti-tuberculosis drugs and combination regimens.

Bactericidal activity of the nitroimidazopyran PA-824 in a murine model of tuberculosis.

The nitroimidazopyran PA-824 has potent in vitro activity against Mycobacterium tuberculosis, a narrow spectrum of activity limited primarily to the M. tuberculosis complex, and no demonstrable cross-resistance to a variety of antituberculosis drugs. In a series of experiments, we sequentially characterized the activity of PA-824 in an experimental murine model of tuberculosis. The minimal effective dose was 12.5 mg/kg of body weight/day. The minimal bactericidal dose (MBD) was 100 mg/kg/day. When PA-824 was used as monotherapy at the MBD, it exhibited promising bactericidal activity during the initial intensive phase of therapy that was similar to that of the equipotent dose of isoniazid in humans. In combination with isoniazid, PA-824 prevented the selection of isoniazid-resistant mutants. Perhaps more importantly, PA-824 also demonstrated potent activity during the continuation phase of therapy, during which it targeted bacilli that had persisted through an initial 2-month intensive phase of treatment with rifampin, isoniazid, and pyrazinamide. Together, these data strongly support further evaluation of PA-824 in combination with first- or second-line antituberculosis drugs to determine its potential contribution to the treatment of drug-susceptible or multidrug-resistant tuberculosis, respectively.

Pharmacokinetic and pharmacodynamic issues in the treatment of mycobacterial infections.

The therapy of mycobacterial infections is challenging for a number of reasons. Because mycobacteria are not susceptible to many classes of antibacterial agents, treatment typically requires the use of antimicrobial drugs that are not commonly used and may have small therapeutic windows. For many species, procedures for drug susceptibility testing and optimal treatment regimens have yet to be defined. Finally, because mycobacteria are generally slow to succumb to antimicrobial agents, therapy must be given with multiple drugs for prolonged periods of time, making it necessary to monitor for drug toxicity, drug interactions, and patient nonadherence. Better understanding of the pharmacokinetics and pharmacodynamics of antimycobacterial agents should improve the therapy of mycobacterial infections. Using current treatment strategies for tuberculosis and Mycobacterium avium complex infections as examples, this review highlights basic pharmacokinetic and pharmacodynamic principles and the rationale for combination chemotherapy that should also be applicable to other mycobacterial infections.

Paucibacillary tuberculosis in mice after prior aerosol immunization with Mycobacterium bovis BCG.

To develop a murine model of paucibacillary tuberculosis for experimental chemotherapy of latent tuberculosis infection, mice were immunized with viable Mycobacterium bovis BCG by the aerosol or intravenous route and then challenged six weeks later with virulent Mycobacterium tuberculosis. The day after immunization, the counts were 3.71 +/- 0.10 log(10) CFU in the lungs of aerosol-immunized mice and 3.65 +/- 0.11 and 4.93 +/- 0.07 log(10) CFU in the lungs and spleens of intravenously immunized mice, respectively. Six weeks later, the lungs of all BCG-immunized mice had many gross lung lesions and splenomegaly; the counts were 5.97 +/- 0.14 and 3.54 +/- 0.07 log(10) CFU in the lungs and spleens of aerosol-immunized mice, respectively, and 4.36 +/- 0.28 and 5.12 +/- 0.23 log(10) CFU in the lungs and spleens of intravenously immunized mice, respectively. Mice were then aerosol challenged with M. tuberculosis by implanting 2.37 +/- 0.13 log(10) CFU in the lungs. Six weeks after challenge, M. tuberculosis had multiplied so that the counts were 6.41 +/- 0.27 and 4.44 +/- 0.14 log(10) CFU in the lungs and spleens of control mice, respectively. Multiplication of M. tuberculosis was greatly limited in BCG-immunized mice. Six weeks after challenge, the counts were 4.76 +/- 0.24 and 3.73 +/- 0.34 log(10) CFU in the lungs of intravenously immunized and aerosol-immunized mice, respectively. In contrast to intravenously immunized mice, there was no detectable dissemination to the spleen in aerosol-immunized mice. Therefore, immunization of mice with BCG by the aerosol route prior to challenge with a low dose of M. tuberculosis resulted in improved containment of infection and a stable paucibacillary infection. This model may prove to be useful for evaluation of new treatments for latent tuberculosis infection in humans.

Cohort study of the treatment of severe HIV-associated nephropathy with corticosteroids.

BACKGROUND: Human immunodeficiency virus-associated nephropathy (HIVAN) results in rapidly progressive azotemia. The effectiveness and safety of corticosteroids in the treatment of HIVAN, however, remains controversial. METHODS: We conducted a retrospective cohort study of patients with biopsy-proven HIVAN and progressive azotemia who were eligible for corticosteroid treatment and who had no clinical or histologic evidence of an alternative cause of acute renal failure. Selected patients were treated with 60 mg of prednisone for one month, followed by a several-month taper. RESULTS: Twenty-one eligible patients were identified. Thirteen subjects had received corticosteroid treatment, whereas eight had not. The mean serum creatinine was 6.2 and 6.8 mg/dL, respectively (P > 0.05). The relative risk (95% CI) for progressive azotemia with corticosteroid treatment at three months was 0.20 (0.05, 0.76, P < 0.05). This association remained significant despite adjustment in separate logistical regression analyses for baseline creatinine, 24-hour proteinuria, CD4 count, history of intravenous drug use, hepatitis B, and hepatitis C. In an additional logistic regression model, using backward stepwise selection of the previously mentioned covariates, only corticosteroid treatment (P = 0.02) and baseline serum creatinine (P = 0.10) were retained within the model. In the corticosteroid-treated group, the mean level of proteinuria decreased by 5.5 g/24 hour (P = 0.01). On long-term follow-up, there was no significant difference in the incidence of hospitalizations (1 per 2.1 vs. 1 per 2.3 patient months) or of serious infections (1 per 2.6 vs. 1 per 2.3 patient months), but there was a significantly longer duration of hospitalization in the corticosteroid-treated group (3.2 vs. 2 days per patient month). At six months, only one of the non-corticosteroid-treated patients but seven of the corticosteroid-treated group continued to have independent renal function (P = 0.06). Three of the corticosteroid-treated group continued to have independent function at two years of follow-up. CONCLUSION: A limited course of corticosteroid therapy in selected patients was beneficial and safe. Further research is required for the role of corticosteroids in the treatment of HIVAN.