Erythromycin Imp. C (EP) :(2S,4aR,4'R,5'S,6'S,7R,8S,9R,10R,12R,14R,15R,16S)-7-ethyl-5',8,9,14-tetrahydroxy-4'-methoxy-4',6',8,10,12,14,16-heptamethyl-15-[[3,4,6-trideoxy-3-(dimethylamino)-ß-D-xylo-hexopyranosyl]oxy]hexadecahydrospiro[5H,11H-.