Milbemycin A4 oxime (5-Ketomilbemycin A4 oxime; 5-Oxomilbemycin A4 5-oxime) is a derivative of Milbemycin A4 and a component of Milbemycin oxime (HY-B0778), both of which have insecticidal and nematicidal activities. Milbemycin A4 oxime (0.05 mg/kg) reduces the number of microfilariae in naturally infected dogs with D. immitis and inhibits the growth of clinical isolates of Candida glabrata (MIC80=16-32 μg/mL). Milbemycin A4 oxime (2.5 μg/mL) blocks the efflux of Fluconazole (HY-B0101) from clinical isolates of Candida glabrata. Milbemycin A4 oxime enhances doxorubicin-induced cell growth inhibition and increases the intracellular accumulation of doxorubicin and P-glycoprotein substrate Rhodamine 123 (HY-D0816) in doxorubicin-resistant but not sensitive MCF-7 breast cancer cells in a concentration-dependent manner.