A derivative of milbemycin A4 and a component of milbemycin oxime; reduces the number of microfilariae of the heartworm D. immitis in naturally infested dogs at 0.05 mg/kg; inhibits the growth of clinical isolates of C. glabrata (MIC80s = 16 to >32 μg/ml); blocks efflux of fluconazole from a clinical isolate of C. glabrata, but not from a strain lacking the efflux pumps CgCDR1 and PDH1, at 2.5 μg/ml; reduces the MICs of fluconazole and 4-nitroquinoline 1-oxide in wild-type C. glabrata; enhances adriamycin-induced inhibition of cell growth in adriamycin-resistant, but not -sensitive, MCF-7 breast cancer cells; increases the intracellular accumulation of adriamycin and rhodamine 123 in adriamycin-resistant, but not -sensitive, MCF-7 breast cancer cells