1 Unitat de Microbiologia, Facultat de Medicina i Ciències de la Salut, Universitat Rovira i Virgili, Reus, Spain; 2 Scientific Institute of Public Health, Brussels, Belgium
Received 2 March 2005; returned 11 March 2005; revised 21 March 2005; accepted 21 March 2005
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Abstract |
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Methods: Twenty-seven clinical isolates were tested, i.e. 10 of Trichosporon asahii, two of Trichosporon mucoides, five of Sporobolomyces salmonicolor and 10 of Rhodotorula glutinis. Drug interactions were assessed by the chequerboard technique using the NCCLS microdilution method (M27-A2). The fractional inhibitory concentration index (FICI) was used to classify drug interactions. Results were interpreted as follows: synergy (FICI 0.5), no interaction (FICI >0.5 and
4.0), or antagonism (FICI >4.0).
Results: Micafungin combined with amphotericin B showed the highest percentage of synergic interactions (78%) followed by micafungin/ravuconazole and micafungin/itraconazole (48% for each), and micafungin/fluconazole and micafungin/voriconazole (34% for each). Antagonism was not observed in any case.
Conclusions: Some of the combinations tested, especially micafungin/amphotericin B, have potential for the treatment of basidiomycetous yeast infections.
Keywords: basidiomycetous yeasts , antifungal susceptibility , combined therapy
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Introduction |
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The aim of this study, therefore, was to determine if the combination micafungin/amphotericin B is active against more strains of T. asahii (n = 10) and thus to confirm the effectiveness of this combination, and also to determine if it is active against other pathogenic yeasts. In addition, we have evaluated the combination of micafungin with some other traditional and new azoles.
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Materials and methods |
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Antifungal agents were obtained as pure powders. Amphotericin B (USP, Rockville, MD, USA), voriconazole (Pfizer Inc., Madrid, Spain), itraconazole (Janssen Pharmaceutica, Beerse, Belgium) and ravuconazole (Bristol-Myers Squibb Company, New Brunswick, NJ, USA) were diluted in dimethyl sulphoxide (Panreac Química S.A., Barcelona, Spain). Micafungin (Fujisawa Pharmaceutical Co. Ltd, Osaka, Japan) and fluconazole (Pfizer Inc., Madrid, Spain) were diluted in sterile distilled water. The MIC was defined as the lowest drug concentration that produced complete absence of growth. Drug interactions were assessed by a chequerboard microdilution method that also included the determination of the MIC of each drug alone in the same plate by using the parameters outlined in the NCCLS document M27-A2.9 Antifungal agents were placed in the rows or in the columns of the trays to perform all possible combinations, with concentrations from 4 to 0.06 mg/L for amphotericin B, 8 to 0.12 mg/L for itraconazole, voriconazole and ravuconazole, 64 to 1 mg/L for fluconazole and 32 to 0.06 mg/L for micafungin. Microplates were read at 48 h for T. asahii and T. mucoides and at 72 h for R. glutinis and S. salmonicolor. Candida krusei ATCC 6258 and C. parapsilosis ATCC 22019 were included as quality controls.
The fractional inhibitory concentration index (FICI) was used to classify drug interaction. The FICI is the sum of the FIC of each of the drugs, which in turn is defined as the MIC of each drug when used in combination divided by the MIC of the drug when used alone. Interaction was considered synergic if the FIC index was 0.5, non-existent if it was >0.5 and
4, and antagonistic if it was >4.10
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Results and discussion |
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In our study, the amphotericin B MICs against R. glutinis were relatively low (0.250.5 mg/L), which agrees with the favourable clinical outcomes observed in infections by Rhodotorula spp. treated with this drug.1,4 However, due to the high toxicity of this drug, other alternatives have to be explored. In our study, micafungin and azoles, with the exception of ravuconazole, were generally inactive against this species. Diekema et al.13 obtained similar results. They tested the activity of eight antifungal agents alone against Rhodotorula species and only amphotericin B and ravuconazole showed low MIC values against this fungi. For this reason, it is an interesting result that in our study all the antifungal combinations showed a high percentage of synergic interactions (6080%) with the exception of micafungin/fluconazole that only showed 20% of synergic interactions. For S. salmonicolor, the amphotericin B MICs were very variable with a 6-fold difference between the lowest and the highest values (0.2516 mg/L). But, in general, these values were high, similar to those of fluconazole and micafungin. Against this species, all the drugdrug interactions were strain dependent. The best combination was micafungin/itraconazole with 60% synergic interactions. The other combinations only showed 2040% synergic interactions. Although these percentages are not as high as for the other species tested, some of these combined therapies could be helpful when amphotericin B fails.
One of the most significant results of this study has been the good activity showed by the combination micafungin/amphotericin B against T. asahii, which was synergic against the 10 strains tested. This confirms the in vivo effectiveness demonstrated by this combination against two strains of this fungus.8 T. asahii is the most frequent species of those tested in this study and causes severe human infections. The fact proved here that the susceptibility of this species to this combination is general and probably not strain dependent emphasizes the potential of this combined therapy for trichosporonosis treatment. Further in vivo studies are warranted to elucidate the potential usefulness of these combination therapies against the species tested in this study.
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Acknowledgements |
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References |
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