Effectiveness of once-weekly rifapentine and moxifloxacin regimens against Mycobacterium tuberculosis in mice

Low isoniazid concentrations and outcome of tuberculosis treatment with once-weekly isoniazid and rifapentine

To understand why once-weekly isoniazid/rifapentine therapy for tuberculosis was less effective than twice-weekly isoniazid/rifampin, we studied human immunodeficiency virus-seronegative patients with either failure (n = 4), relapse (n = 35), or cure (n = 94), recruited from a comparative treatment trial. In multivariate analyses that were adjusted for severity of disease, low plasma concentrations of isoniazid were associated with failure/relapse with once-weekly isoniazid/rifapentine (median isoniazid area under the concentration-time curve for 12 hours after the dose [AUC(0-12)] was 36 microg x hour/ml in failure/relapse versus 56 microg x hour/ml in control cases p = 0.005), but not with twice-weekly isoniazid/rifampin. Furthermore, two patients who relapsed with Mycobacterium tuberculosis monoresistant to rifamycin had very low concentrations of isoniazid. Finally, isoniazid acetylator status determined by N-acetyltransferase type 2 genotype was associated with outcome with once-weekly isoniazid/rifapentine (p = 0.03) but not twice-weekly isoniazid/rifampin. No rifamycin pharmacokinetic parameter was consistently and significantly associated with outcome (p > 0.10). Because low isoniazid concentrations were associated with failure/relapse, a drug with consistently greater area under the concentration-time curve than isoniazid may be needed to achieve highly active once-weekly therapy with rifapentine.

Current thinking on the management of tuberculosis

High-income countries are moving toward tuberculosis (TB) elimination. Sophisticated diagnostic tests and effective treatment regimens are readily available. The range of available resources even makes effective treatment of multidrug-resistant tuberculosis (MDRTB) possible. The introduction of highly active antiretroviral therapy and specific TB control measures has reduced the incidence of HIV-associated TB disease. Unfortunately, the situation in low-income countries that carry 95% of the global TB burden is less positive. TB diagnosis still relies upon sputum smear microscopy. The management of MDRTB remains problematic though guidelines for DOTS-plus programs have been developed, and cheaper second-line drugs are becoming available. The HIV epidemic continues to confound TB control efforts, particularly in sub-Saharan Africa. The appropriate package of interventions for controlling HIV/TB disease remains undefined and unimplemented. The international community must provide the funding and technical support to address the alarming dichotomy in TB control that exists between rich and poor countries.

Long-term tolerance and effectiveness of moxifloxacin therapy for tuberculosis: preliminary results

The resurgence of tuberculosis is a major problem. Increasing multiple resistance to current drugs used for therapy, non-compliance to therapy or co-morbidity are challenging problems that do not allow use of standard therapy in all patients. Quinolones are claimed to be active drugs in TB infection. Moxifloxacin shows the highest intracellular concentration in vitro and in experimental animals, but long-term tolerability is unknown. Our aim was to observe in compliant patients, not eligible for standard therapy, the effect of 6 months of therapy with moxifloxacin, isoniazid and rifampin. Nineteen patients, a control group, were observed for the same period under therapy with streptomycin, pirazinamide, rifampin, isoniazid. The patients were affected by indolent miliary pattern and concomitant lymphoma or leukemia in 3 cases; rare nodular involvement with genitourinary diseases in 3 others; segmental to lobar involvement in 4 others with concomitant multidrug resistance, bone localization, hepatitis. The control group was more uniform and showed segmental to lobar nodular involvement with pleuritis in 3 patients, together with hepatitis in 3. Monthly checks of blood gas analysis, chest X-ray, functional testing, serum titers of antibodies against antigen 60, sputum slides and complete chemical analysis were performed. A follow-up visit was performed 1 month after therapy. Patients under moxifloxacin therapy experienced no toxicity, almost complete sterilization and remission of the disease. Sterilization was obtained in 15 days. Patients under standard therapy also had a good clinical outcome, although therapy was delayed in 3 cases because of increased transaminases within the first 15 days of therapy. Moxifloxacin seems to be well tolerated and combination therapy including moxifloxacin for TB seems to be as active as the standard therapy in patients with complex illness.

Sterilizing activities of fluoroquinolones against rifampin-tolerant populations of Mycobacterium tuberculosis

The bactericidal activities of ciprofloxacin, ofloxacin, levofloxacin, moxifloxacin, and gatifloxacin were tested in three models of rifampin-tolerant Mycobacterium tuberculosis persisters. Model 1 was a 100-day-old, unshaken, anaerobically adapted culture in which serial dilutions of the quinolones were incubated for 5 days and CFU counts were then done In models 2 and 3, 100 mg of rifampin/liter was added to the 100-day culture for 5 or 7 days to produce tolerant organisms that did not grow on plates; the rifampin was then washed off, fresh medium was added to allow recovery of growth on plates, and the culture was incubated for 7 days before CFU counts. In model 2, the quinolones were added after rifampin had been washed off, whereas in model 3 the quinolones were added to the cultures containing rifampin. In models 1 and 2, ciprofloxacin had the least bactericidal activity, ofloxacin and levofloxacin had greater activities, and moxifloxacin and gatifloxacin had the greatest activities. In model 3, ofloxacin had no detectable activity whereas moxifloxacin killed about log(10) 0.279 CFU of the persisters per ml at concentrations attainable in lesions; isoniazid had virtually no activity. These findings predict that ofloxacin will not be found to have effective sterilizing activity in clinical studies now planned whereas moxifloxacin will be able to shorten treatment.

Activities of moxifloxacin alone and in combination with other antimicrobial agents against multidrug-resistant Mycobacterium tuberculosis infection in BALB/c mice

The activity of moxifloxacin was enhanced by the addition of ethionamide but not by that of cycloserine, thiacetazone, capreomycin, para-aminosalicylic acid, or linezolid in BALB/c mice infected with a strain of Mycobacterium tuberculosis resistant to isoniazid, rifampin, and six other drugs. These observations are important for the therapy of multidrug-resistant tuberculosis.

A prospective, randomized, double-blind study of the tolerability of rifapentine 600, 900, and 1,200 mg plus isoniazid in the continuation phase of tuberculosis treatment

Once-weekly rifapentine 600 mg plus isoniazid (INH) during the continuation phase treatment of tuberculosis is associated with a relapse rate higher than that of twice-weekly rifampin plus INH. The safety and tolerability of higher rifapentine doses need to be determined. We conducted a prospective, randomized, double-blind trial of rifapentine at three doses (600, 900, and 1,200 mg) plus INH 15 mg/kg once weekly in the continuation phase treatment of culture-positive tuberculosis in 150 human immunodeficiency virus-seronegative adults. Outcome measures were discontinuation of therapy for any reason and adverse events on therapy. Treatment was discontinued in 3 of 52 (6%), 2 of 51 (4%), and 3 of 47 (6%) in the rifapentine 600-, 900-, and 1,200-mg treatment arms, respectively. Only one discontinuation, in the rifapentine 1,200-mg arm, was due to an adverse event possibly associated with study therapy. There was a trend toward more adverse events, possibly associated with study therapy, in the highest-dose arms (p = 0.051). Rifapentine 900-mg, once-weekly dosing appears to be safe and well tolerated and is being evaluated in Phase III efficacy trials of treatment of latent tuberculosis. Further evaluation of the safety and tolerability of rifapentine 1,200 mg is warranted.

Bactericidal activity of increasing daily and weekly doses of moxifloxacin in murine tuberculosis

Moxifloxacin (MXF) is a new 8-methoxyquinolone with potent activity against Mycobacterium tuberculosis and a half-life of 9 to 12 h in humans. Previous in vivo studies using daily doses of 100 mg/kg of body weight have demonstrated bactericidal activity comparable to that of isoniazid (INH) in a murine model of tuberculosis (TB). Recent pharmacokinetic data suggest that MXF may have been underadministered in these studies and that a 400-mg/kg dose in mice better approximates the area under the concentration-time curve obtained in humans after a 400-mg oral dose. Therefore, the bactericidal activity of MXF in doses up to 400 mg/kg given daily or weekly for 28 days was assessed in mice infected intravenously with 5 x 10(6) CFU of M. tuberculosis. INH was used as a positive control. After 3 days of daily therapy, the CFU counts from splenic homogenates for mice treated with MXF in doses of 100 to 400 mg/kg/day were lower than those from pretreatment controls. No significant differences in CFU counts were seen when mice receiving INH or MXF at 50 mg/kg/day were compared to pretreatment controls. After 28 days of therapy, dose-dependent reductions in CFU counts in splenic homogenates were seen for daily MXF therapy. The maximum bactericidal effect was seen with daily doses of 400 mg/kg, which resulted in a reduction in CFU counts of 1 log(10) greater than that with INH treatment, although the difference was not statistically significant. CFU counts from lung homogenates after 28 days of therapy were significantly lower in all treatment groups than in untreated controls. The weekly administration of MXF in doses ranging from 50 to 400 mg/kg resulted in no significant bactericidal activity. Mice receiving daily MXF doses of 200 and 400 mg/kg/day failed to gain weight and appeared ill after 28 days of therapy, findings suggestive of drug toxicity. In conclusion, MXF has dose-dependent bactericidal activity against M. tuberculosis in the mouse when given in doses up to 400 mg/kg, where its pharmacokinetic profile better approximates that of standard human dosages. Combination regimens which take advantage of the enhanced pharmacodynamic profile of MXF at these doses have the potential to shorten the course of antituberculous therapy or allow more intermittent (i.e., once-weekly) therapy and should be evaluated in the mouse model of TB.