The pharmacokinetics and pharmacodynamics of pulmonary Mycobacterium avium complex disease treatment.

RATIONALE: Currently recommended multidrug treatment regimens for Mycobacterium avium complex (MAC) lung disease yield limited cure rates. This results, in part, from incomplete understanding of the pharmacokinetics and pharmacodynamics of the drugs. OBJECTIVES: To study pharmacokinetics, pharmacodynamics, and drug interactions of multidrug treatment regimens in a large cohort of patients with MAC lung disease. METHODS: We retrospectively collected pharmacokinetic data of all patients treated for MAC lung disease in the Adult Care Unit at National Jewish Health, Denver, Colorado, in the January 2006 to January 2010 period; we retrospectively calculated areas under the time-concentration curve (AUC). Minimum inhibitory concentrations (MIC) of their MAC isolates were retrieved for pharmacodynamic calculations. MEASUREMENTS AND MAIN RESULTS: We included 531 pharmacokinetic analyses, performed for 481 patients (84% females; mean age, 63 yr; mean body mass index, 21.6). Peak serum concentrations (C(max)) below target range were frequent for ethambutol (48% of patients); clarithromycin (56%); and azithromycin (35%). Concurrent administration of rifampicin led to 68%, 23%, and 10% decreases in C(max) of clarithromycin, azithromycin, and moxifloxacin. C(max)/MIC or AUC/MIC ratios associated with bactericidal activity were seldom met; 57% of patients achieved target ratios for ethambutol, versus 42% for clarithromycin, 19% for amikacin, 18% for rifampicin, and 11% for moxifloxacin. CONCLUSIONS: Currently recommended regimens for MAC lung disease yield important pharmacologic interactions and low concentrations of key drugs including macrolides. Pharmacodynamic indices for rifampicin, clarithromycin, amikacin, and moxifloxacin are seldom met. This may partly explain the poor outcomes of currently recommended treatment regimens. Trials of new drugs and new dosing strategies are needed.

In vitro synergy between clofazimine and amikacin in treatment of nontuberculous mycobacterial disease.

Disease caused by nontuberculous mycobacteria (NTM) is increasing in frequency. The outcome of treatment for NTM lung disease is poor, particularly lung disease caused by Mycobacterium simiae and M. abscessus. Exploring synergy between active available drugs is a sensible way forward given the lack of new active drugs. We tested for synergy between amikacin and clofazimine, using standardized methods, in 564 consecutive clinical isolates identified as 21 species of rapidly growing mycobacteria, 16 clinical M. avium complex isolates, and 10 M. simiae isolates. Clofazimine and amikacin are each active in vitro against NTM; 97% (n = 548) of the rapid growers revealed MICs of clofazimine of ≤1 µg/ml, and 93% (n = 524) proved susceptible to amikacin. The combination showed significant synergistic activity in 56 of 68 (82%) eligible M. abscessus isolates, 4 of 5 M. chelonae isolates, and 1 M. fortuitum and 1 M. cosmeticum isolate, with 4- to 8-fold decreases in MICs to both drugs. Significant synergy could also be demonstrated against all M. avium complex and M. simiae isolates, with fractional inhibitory concentrations of <0.5. Clofazimine and amikacin show significant synergistic activity against both rapidly and slowly growing nontuberculous mycobacteria. The safety and tolerability of adding clofazimine to amikacin-containing regimens should be tested in clinical trials, and the results of susceptibility tests for these two compounds and their combination merit clinical validation. Synergy between clofazimine and other antibiotics with intracellular targets should be explored.

Are phylogenetic position, virulence, drug susceptibility and in vivo response to treatment in mycobacteria interrelated?

Phylogenetic analyses on the basis of multiple house-keeping genes and whole genome sequences have offered new insights in the phylogeny of the genus Mycobacterium. This genus yields obligate pathogens, the M. tuberculosis complex and M. leprae, as well as opportunistic pathogens (e.g. M. avium, M. intracellulare, M. kansasii, M. marinum, M. malmoense) and saprophytes (e.g. M. phlei, M. sphagni, M. gordonae). The most virulent mycobacteria, the M. tuberculosis complex, M. leprae and the M. kansasii-M. szulgai-M. marinum-M. ulcerans group are phylogenetically related and infections by these organisms are better treatable than those caused by less virulent and phylogenetically more distantly related Mycobacterium species. The most virulent Mycobacterium species are also characterized by high levels of natural drug susceptibility. In this paper, we review studies of phylogeny, drug susceptibility, and clinical significance to support our hypothesis that drug susceptibility in mycobacteria is acquired and reflects the low level of competition in -and adaptation to- a closer-to-human (environmental) niche. In turn, mycobacteria that inhabit the most competitive environmental niches are the least adapted to humans, thus of low clinical significance, but most tolerant to antibiotics derived from microbes with which they share their habitat, lowering the chances of cure in case of infection.

Drug susceptibility testing and pharmacokinetics question current treatment regimens in Mycobacterium simiae complex disease.

The Mycobacterium simiae complex bacteria can cause opportunistic infections in humans. In the case of definite disease, there are no evidence-based treatment regimens and outcomes are very disappointing. To increase the evidence base underpinning treatment regimens for M. simiae complex disease, drug susceptibility patterns and rifampicin/ethambutol synergy were assessed retrospectively in 69 clinical M. simiae complex isolates from 60 patients (22 patients with M. simiae, 24 with Mycobacterium lentiflavum, 8 with Mycobacterium triplex, 5 with Mycobacterium parascrofulaceum and 1 with Mycobacterium stomatepiae) submitted to the mycobacteriology laboratory at National Jewish Health (Denver, CO). Quantitative drug susceptibility testing (DST) was performed using the radiometric BacTec 460 macrodilution method. Results were related to pharmacokinetic (PK) measurements, where available. All M. simiae complex species proved susceptible to clarithromycin and, to a lesser extent, rifabutin, clofazimine, streptomycin and moxifloxacin. Synergy or additive action between rifampicin and ethambutol was observed for all species except M. simiae. Mycobacterium simiae is poorly susceptible in vitro to rifampicin and ethambutol alone as well as in combination; PK measurements support the limited efficacy of these drugs against M. simiae. The triple-drug regimen of a rifamycin, ethambutol and a macrolide may be advised to treat disease caused by M. lentiflavum, M. triplex, M. parascrofulaceum and M. stomatepiae; for M. simiae, this regimen appears less active. These findings may partly explain the limited treatment results in M. simiae disease. A treatment regimen including a macrolide, moxifloxacin and one or two additional drugs based on DST results may be advisable; clofazimine and amikacin or streptomycin are potential candidates.

Inhibition of M. tuberculosis in vitro in monocytes and in mice by aminomethylene pyrazinamide analogs.

Pyrazinamide is unusual among anti-tuberculous agents in its ability to promote a durable cure and shorten the duration of therapy. Yet the basis for this effect is not well understood. A particularly effective strategy for the development of new drugs can be to synthetically manipulate the well-established structures to improve either the spectrum of activity or some pharmacological properties. Similar to previously described aminomethylene amides such as morphazinamide, it was found that novel aminomethylene amides can have in vitro activity at higher than the very acidic pH conditions where pyrazinamide is inactive as well as retaining activity against pyrazinamide-resistant M. tuberculosis. These new compounds have shown an improved anti-tuberculous activity in infected human macrophages relative to pyrazinamide. Compound 1, in combination with rifamycin, was especially effective in both infected human macrophages and in a murine model of infection. The activity of these analogs against pyrazinamide-resistant strains suggests that the development of second generation pyrazinamide analogs may be especially fruitful.

Cough-generated aerosols of Mycobacterium tuberculosis: a new method to study infectiousness.

The concentration and size distribution of infectious aerosols produced by patients with pulmonary tuberculosis (TB) has never been directly measured. We aimed to assess the feasibility of a method that we developed to collect and quantify culturable cough-generated aerosols of Mycobacterium tuberculosis. Subjects were recruited from a referral hospital and most had multidrug-resistant TB. They coughed into a chamber containing microbial air samplers while cough frequency was measured during two 5-minute sessions. Cough-generated aerosol cultures were positive in 4 of 16 subjects (25%) with smear-positive pulmonary TB. There was a rapid decrease in the cough-generated aerosol cultures within the first 3 weeks of effective treatment. Culture-positive cough aerosols were associated with lack of treatment during the previous week (p = 0.007), and there was a trend in the association with cough frequency (p = 0.08). The size distributions of these aerosols were variable, but most particle sizes were in the respirable range. Quantification of viable cough-generated aerosols is feasible and offers a new approach to study infectiousness and transmission of M. tuberculosis and other airborne pathogens.