Acute and chronic effects of flucytosine on amphotericin B nephrotoxicity in rats

The combination of intravenous flucytosine (FC) in 0.9% saline (NaCl) and amphotericin B (AmB) provides synergistic antifungal activity and is associated with a lower incidence of nephrotoxicity than with AmB treatment alone. This study was conducted to examine whether flucytosine can influence renal function and whether it can modify the acute and chronic renal responses to AmB in the rat. In the in situ perfused rat kidney, FC at a concentration of 10 mg/kg/min for 15 min had a vasodilator effect, increasing renal blood flow by 2.5 +/- 0.7 ml/min, an effect not observed with vehicle. After the infusion of FC was stopped for 15 min, AmB induced a decrease in renal blood flow similar to that with both FC and vehicle. In a second series of studies, AmB (5 mg/kg/day intraperitoneally) was administered to four groups of rats for 7 days. In addition, the following groups received the intravenous daily interventions indicated: group 1, 5% dextrose in water (15 ml/kg/12 h); group 2, FC (150 mg/kg/12 h) in 0.9% saline (15 ml/kg/12 h); group 3, 0.9% saline (15 ml/kg/12 h); and group 4, FC (150 mg/kg/12 h) in 5% dextrose in water. Group 1 sustained a 77% decrease in creatinine clearance over the 7 days and a threefold increase in serum creatinine concentration (P of < 0.05). Groups 2, 3, and 4 sustained significantly less nephrotoxicity, with no change in serum creatinine concentration and only 38, 41, and 53% decreases in creatinine clearance, respectively (P of < 0.05), compared with that for group 1. AmB levels in renal tissue varied inversely to creatinine clearance (r of 0.57, P of < or = 0.005). However, no significant differences were found in levels in tissue between groups (P of 0.06). The results of this study suggest that FC has a small but significant effect in reducing chronic AmB-induced nephrotoxicity. This amelioration of renal injury is independent of saline administration. There was evidence that the extent of renal uptake of AmB related to the efficiency of renal function at the end of the experiment.