Positive interaction of nikkomycins and azoles against Candida albicans in vitro and in vivo

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Abstract
Nikkomycins X and Z (NZ), competitive inhibitors of fungal chitin synthetase, were combined with azoles in a series of in vitro checkerboard assays to test for synergism against Candida spp. All combinations of nikkomycins and azoles tested resulted in marked synergistic activity against an isolate of Candida albicans, with fractional inhibitory concentration indices ranging from 0.016 to 0.28. No synergistic effect was demonstrable with isolates of C. tropicalis, C. parapsilosis, or C. krusei, though results for the latter two were suggestive of an additive effect. In survival models of mice infected intravenously with C. albicans, NZ administered singly in doses ranging from 5 to 50 mg/kg of body weight twice a day was able to delay the onset of mortality but showed no dose-response effect. The combination of NZ and the azole R 3783 administered orally in a ratio of 8:1 to 40:1 or greater (wt/wt) enhanced survival better than did the drugs given individually, but this effect was less evident for combinations involving fluconazole. In short-term organ load assays with outbred mice infected intravenously with C. albicans, high ratios of NZ to R 3783 reduced the CFU per gram in kidneys more significantly than did the drugs individually. Statistically significant reductions were not seen for short-term fungal burden assays using combinations of NZ and fluconazole in outbred mice or in inbred mice more susceptible to candidiasis. In a model of rat vaginal candidiasis, the combination of NZ and R 3783 administered either orally or vaginally was more effective than the drugs used singly. Thus, under certain conditions, combination therapy with nikkomycin and select azoles may offer promise for an increased therapeutic effect in candidiasis.