Relapses in multibacillary leprosy patients after stopping treatment with rifampin-containing combined regimens. Marchoux Chemotherapy Study Group

During the decade between the mid 1970s and the mid-1980s, 12 rifampin (RMP)-containing combined regimens were tested among lepromatous leprosy patients in the Institut Marchoux. The 384 patients who were seen at least once during the period beginning 12 months after completion of treatment were considered eligible for analysis of the relapse rate. By the end of May 1991, relapse, manifested by a significant increase of the bacterial index (BI) and the appearance of new lesions with a BI greater than that of preexisting lesions, had been observed in 68 (17.7%) of these patients. Relapse was confirmed by the presence of viable Mycobacterium leprae in skin biopsy specimens obtained from 54 of the first 61 cases; virtually all of the isolated strains remained susceptible to RMP. The relapses occurred late, about 5 +/- 2 years after stopping treatment; the shorter the duration of RMP administration, the earlier the appearance of the relapse. The variations of the relapse rate among regimens were considerable: total relapse rate ranged from 2.9% to 27.8%, and the relapse rate per 100 patient-years of observation ranged from 0.8 to 6.9. Among the 12 regimens, only the WHO/MDT yielded an acceptable relapse rate (defined as a rate lower than 1.0 per 100 patient-years). However, because the mean duration of follow up was shortest among the patients treated with WHO/MDT, the relative low relapse rate among these patients must be interpreted with great caution.

Antagonism between isoniazid and the combination pyrazinamide-rifampin against tuberculosis infection in mice

Mice that had been inoculated intravenously with 6.30 log10 Mycobacterium tuberculosis H37Rv 14 days earlier were administered one of three combinations of drugs, i.e., isoniazid (INH)-rifampin (RMP)-pyrazinamide (PZA), INH-RMP, and RMP-PZA, during an initial 2-month period to mimic the initial phase of chemotherapy for human tuberculosis and during a later 4-month period to mimic the continuation phase of chemotherapy. At the end of the initial phase, all three combined regimens were found to have been highly effective in terms of the number of CFUs in the spleens of infected mice. The bactericidal activities of INH-RMP-PZA and INH-RMP were similar, whereas that of RMP-PZA was significantly greater. The spleens of all of the mice that had been treated initially with INH-RMP-PZA were culture negative by the end of 6 months of treatment, regardless of the regimen employed during the continuation phase. However, after an additional period of 6 months without treatment, the proportion of spleen culture positivity, or relapse rate, was significantly smaller in the subgroup treated with RMP-PZA during the continuation phase than in the subgroups treated with INH-RMP-PZA or INH-RMP; the relapse rate did not differ significantly between the latter two subgroups. These results suggest that antagonism occurs between INH and the combination RMP-PZA during both the initial and continuation phases of chemotherapy, compromising the benefit conferred by the addition of PZA to the combined regimen. The preliminary pharmacokinetic analysis suggested that the pharmacological interaction between INH and RMP was very likely to be involved in the mechanism of antagonism, as concomitant treatment with INH had significantly reduced the peak serum level and the area under the serum concentration-time curve of RMP in mice.

In vitro and in vivo activities of sparfloxacin (AT-4140) against Mycobacterium tuberculosis

The in vitro and in vivo activities of sparfloxacin (AT-4140) against M. tuberculosis are reported. The MICs of sparfloxacin for 50% and 90% of 18 clinical isolates were, respectively, 0.25 and 0.5 mg/l, one or two dilutions lower than that of ciprofloxacin and ofloxacin. In mice infected intravenously with 0.1 mg M. tuberculosis H37Rv strain, the minimal effective dosage of sparfloxacin, as assessed by survival rate, spleen enlargement and gross lung lesions, was 12.5 mg/kg. The activities of various regimens were in the following rank order: INH 25 mg/kg = sparfloxacin 50-100 mg/kg greater than ofloxacin 300 mg/kg greater than (or =) sparfloxacin 25 mg/kg greater than sparfloxacin 12.5 mg/kg greater than (or =) ofloxacin 200 mg/kg greater than ofloxacin 100 mg/kg greater than (or =) negative control. Therefore, on a weight to weight basis, sparfloxacin was six to eight-fold more active against M. tuberculosis infection in mice than ofloxacin. In addition, WIN 57273, a new broad-spectrum fluoroquinolone, at a dosage of 100 mg/kg daily, was inactive against M. tuberculosis infection.

Effect of pH on the in vitro potency of clarithromycin against Mycobacterium avium complex

Employing 7H11 agar medium at pH 6.6, the MICs of clarithromycin for 50% (MIC50) and 90% (MIC90) of 19 strains of Mycobacterium avium complex were 8 and 16 micrograms/ml, respectively. However, the MICs were 2 to 3 log2 dilutions lower in the 7H11 medium adjusted to pH 7.4, and the MICs on 10% OADC (oleic acid-albumin-dextrose-catalase)-enriched Mueller-Hinton agar at pH 7.3 were also 2 log2 dilutions lower than those measured on 7H11 agar at pH 6.6. Therefore, clarithromycin is more active at a physiologic than at an acidic pH.

Immunobinding assay for the speciation of avian mycoplasmas adapted for use with a 96-well filtration manifold

An immunobinding assay capable of distinguishing among Mycoplasma synoviae, M. gallisepticum, M. gallopavonis, and M. meleagridis was developed. A low-protein-binding membrane filter served as the solid support, and a 96-well microsample filtration manifold was used. The assay detected 50 ng of mycoplasmal protein, or approximately 3 x 10(4) colony-forming units, from pure or mixed cultures. No cross-reactions were observed among the mycoplasma species tested. The assay was inexpensive, easy to interpret, and required approximately 3 hr to perform. The 96-well format allowed screening of numerous cultures and use of several antisera in a single assay.

Effectiveness of clarithromycin and minocycline alone and in combination against experimental Mycobacterium leprae infection in mice

As determined by the proportional bactericide method, clarithromycin had strong bactericidal activity against Mycobacterium leprae. Clarithromycin was administered to mice by gavage as 20 daily doses at dosages of 12.5 to 50 mg/kg of body weight. At a dosage of 25 mg/kg, minocycline was more active than clarithromycin at a dosage of 50 mg/kg. Additive effects were displayed with the combination of clarithromycin (50 mg/kg) and minocycline (25 mg/kg), both of which were administered daily by gavage, and of clarithromycin and minocycline, both of which were administered daily by gavage at dosages of 25 mg/kg each, with rifampin at a single oral dose of 10 mg/kg.

Activities of pefloxacin and ofloxacin against mycobacteria: in vitro and mouse experiments

The minimal inhibitory concentrations for 90% of strains (MIC90) of ofloxacin against Mycobacterium tuberculosis and Mycobacterium xenopi was 2 mg/l. This was three dilutions lower than that of pefloxacin and was well within the range of drug concentrations achievable in man. The antituberculosis activities of both quinolones were independent of resistance of the strains to other antimycobacterial agents. Mycobacterium avium-intracellulare was resistant to both compounds with MIC90s greater than 16 mg/l. The maximum serum levels (Cmax) of both compounds increased proportionally with increasing dose size. The terminal elimination half-life (T1/2) of pefloxacin was longer than that of ofloxacin, but the T1/2 of both compounds in mice were much shorter than in man. The area under the concentration curve (AUC) of pefloxacin was double than that of ofloxacin. In the mouse, pefloxacin at doses up to 150 mg/kg daily was inactive against M. tuberculosis infection: in terms of survival rate the minimal effective dose of ofloxacin against M. tuberculosis infection was 150 mg/kg daily when given by gavage or by incorporation into the mouse diet at a concentration of 0.1%, but in terms of cfu counts, ofloxacin 150 mg/kg daily only displayed a moderate degree of activity similar to ethambutol 100 mg/kg daily. The therapeutic effects of ofloxacin against M. tuberculosis infection were dose-related: 300 mg/kg daily by gavage or 0.4% in mouse diet displayed much better therapeutic effects than lower dosages. Since the AUC in mice treated with ofloxacin 150 mg/kg daily is close to that in man treated with a clinically tolerated dose--600 mg daily--such a dosage may be only moderately effective against human tuberculosis.