Effects of clarithromycin and rifabutin alone and in combination on intracellular and extracellular replication of Mycobacterium avium

Abstract

The combined effect of clarithromycin and rifabutin against Mycobacterium avium multiplying either within human monocyte-derived macrophages or extracellularly in a liquid medium was additive: both MICs and MBCs were twofold lower for the combination than they were for each drug alone. Prolonged exposure for 4 weeks of M. avium-infected macrophages to combined concentrations that were only twofold greater than the MICs resulted in a 100-fold decrease in the number of viable bacteria, while in the drug-free controls a 100-fold or greater increase in comparison with the initial viable counts took place. Comparison of this effect with the results of the prolonged exposure to each drug alone suggested that under these experimental conditions rifabutin enhanced the antimicrobial activity of clarithromycin against intracellular bacteria. At the same time, inhibition of intracellular growth by a 2-h pulsed exposure of the infected macrophages to the combination of the two drugs was not different from the effect induced by clarithromycin alone. In conclusion, clarithromycin played the major role in the antimicrobial activity of the tested combination, while rifabutin may have enhanced this effect during a prolonged exposure of the intracellular bacteria to these two agents.Combinations of clarithromycin with a variety of other drugs have been investigated in vitro in cell-free culture media and macrophages (3,7,9,10,16,17). The overall analyses of these data indicated that the interaction in these combinations tested against Mycobacterium avium was additive rather than synergistic (2). The effect of this combination for the treatment and prevention of disseminated M. avium infection in patients with AIDS is under investigation. The aim of the present study was to evaluate the activity of clarithromycin in combination with rifabutin against M. avium in a cell-free culture medium and human monocyte-derived macrophages. The study included an evaluation of the antimicrobial activity during prolonged exposure and the effect of a drug combination given to infected macrophages by pulsed exposure.MATERUILS AND METHODS Antimicrobial agents. Rifabutin (Adria Laboratories, Pharmacia, Columbus, Ohio) was dissolved first in methanol (640 jig/ml) and was then diluted further in distilled water to make appropriate working solutions. Clarithromycin (Abbott Laboratories, Abbott Park, Ill.) was first dissolved in dimethyl sulfoxide (1,280 jig/ml) and was then diluted further in phosphate buffer (pH 6.5).Test strains. Three strains identified as M. avium by the Gen-Probe (San Diego, Calif.) technique were used for the studies. These strains, isolated from blood samples obtained from patients with AIDS, were used in our previous studies (8,12,13). They were preserved in frozen 7H9 broth culture aliquots at -70°C. For each experiment, a subculture in 7H9 broth was made from a frozen aliquot.Antimicrobial activity against extracellular bacteria. The MIC was defined as the lowest drug concentration that inhibited more than 99% of the bacteria...

Comparison of activities of rifapentine and rifampin against Mycobacterium tuberculosis residing in human macrophages

“…This model has been described in detail in our previous publications (13,14). The human mononuclear cells were separated by Ficoll-Hypaque gradient centrifugation and placed in 35-mm-diameter plastic petri plates.…”

Mycobacterium ulcerans infection in a child from angola: diagnosis by direct detection and culture

“…The antimycobacterial regimen consisted of ciprofloxacin, rifampicin, dapsone and clarithromycin. This was partially based on the report of Goutzamanis & Gilbert 1995) suggesting that rifampicin and dapsone were effective against M. ulcerans, and on the synergistic antimycobacterial activity between clarithromycin and rifampicin against atypical mycobacteria as shown by Mor et al (1994). Ciprofloxacin alone may have only weak activity against M. ulcerans, because after 22 days of treatment, the ulcer remained positive with M. ulcerans.…”

“…This was partially based on the report of Goutzamanis & Gilbert 1995) Portaels et al (1996); ϩ, Ͼ 85% of the strains were positive; Ϫ , Ͻ 15% of the strains were positive; M, 50-85% of strains positive; F, 15-49% of strains positive. synergistic antimycobacterial activity between clarithromycin and rifampicin against atypical mycobacteria as shown by Mor et al (1994). Ciprofloxacin alone may have only weak activity against M. ulcerans, because after 22 days of treatment, the ulcer remained positive with M. ulcerans.…”

Papel de Mycobacterium avium paratuberculosis en la etiopatogenia de la enfermedad de Crohn

“…Los estudios realizados in vitro han puesto de manifiesto que, al igual que otras micobacterias atípicas, presenta una gran resistencia a los fármacos antituberculosos clásicos 29,39 . Estos mismos estudios demostraron la eficacia de los macrólidos y la rifabutina 80,81 . Actualmente, aunque se desconoce cuál es el tratamiento de elección, se considera que se necesitan al menos 2 fármacos con actividad demostrada frente a M. avium paratuberculosis administrados durante un mínimo de 6 a 12 meses para que el tratamiento sea efectivo 39 .…”