High and Sustained Release of the Novel Echinocandin Rezafungin from Bone Cement: An In Vitro Comparison with Liposomal Amphotericin B and Micafungin.

Abstract

Fungal periprosthetic joint infections (PJIs) are difficult-to-treat infections due to the complexity of fungal biofilm and to the limited number of antifungal agents that both elute effectively and remain active when incorporated into polymethylmethacrylate (PMMA) bone cement. Rezafungin (REZA), a next-generation, long-acting echinocandin with antibiofilm activity, may overcome these limitations. This study evaluated the in vitro elution kinetics of REZA from PMMA, assessed whether antibiofilm activity was maintained after elution, and compared its performance with micafungin (MICA) and gold standard liposomal amphotericin B (AmB). A commercial gentamicin-loaded bone cement was mixed with REZA or MICA at 0.5 and 1% and with AmB at 0.5%. Standardized samples (n = 3 per group) were incubated in phosphate-buffered saline under agitation. Eluates were collected at 10 time points from one hour to six weeks and quantified by LC-MS (AmB) or HPLC (MICA and REZA). Cumulative drug release (area under the curve (AUC)) was calculated for each group. The antifungal activity of first-hour eluates of each drug was tested against 12 strains of Candida spp., using a 24-hour biofilm inhibition assay. The REZA achieved the highest and most sustained elution, with 24-hour concentrations of 1,789 μg/mL (1%) and 1,738 μg/mL (0.5%), exceeding AmB 0.5% by greater than 150-fold. The AUC₀-₆ weeks ranked: REZA-1 greater than REZA-0.5 greater than MICA much greater than AmB-0.5. The REZA remained more than 10,000-fold above its minimum inhibitory concentration (MIC for C. albicans 0.008 μg/mL) throughout six weeks, while AmB dropped below its MIC (one μg/mL) after four hours. All antifungals reduced biofilm metabolic activity by greater than 85%, confirming retained antifungal activity. The REZA eluted from PMMA at high concentrations, releasing significantly more drug than MICA or AmB. Drug release was consistent with a concentration-dependent elution. All three antifungal agents retained metabolic activity, but REZA surpassed its MIC (C. albicans) by more than 10,000-fold, a margin that may translate into enhanced antibiofilm activity.