Amphotericin B is cytotoxic at locally delivered concentrations.

Background: Orthopaedic fungal infections are commonly treated with systemic amphotericin, which has a narrow therapeutic index and is associated with systemic toxicities. Local delivery of amphotericin has been described yet is poorly understood. As with bacterial infections, fungal infections are associated with biofilm. However, it is unclear whether experience with local delivery of antibacterials can be applied to local antifungal delivery.

Questions/purposes: We asked whether (1) 100 to 1000 μg amphotericin/mL caused osteoblast cell death; (2) 1 to 10 μg amphotericin/mL caused sublethal toxicity to osteoblasts and fibroblasts; and (3) sublethal amphotericin toxicity could be reversed.

Methods: Mouse osteoblasts and fibroblasts were exposed in vitro to amphotericin concentrations of 0, 1, 10, 100, and 1000 μg/mL for 5 hours or 0, 1, 5, and 10 μg/mL for 7 days and then 3 days with no amphotericin. Cell morphology on light microscopy and proliferation assays (alamarBlue(®) and MTT) were used as measures of toxicity.

Results: Amphotericin concentrations of 100 μg/mL and above caused cell death; 5 to 10 μg/mL caused abnormal cell morphology and decreased proliferation. Cells regained normal morphology and resumed cell proliferation within 3 days after removal of amphotericin.

Conclusions: In this in vitro study, amphotericin was cytotoxic to osteoblasts and fibroblasts at concentrations achievable by local delivery.

Clinical Relevance: If local concentrations of 100 to 1000 times the minimum inhibitory concentration are necessary to treat biofilm-associated fungal infections as they are for bacterial infection, cell toxicity at the local depot site should be considered.