erythrocin n an antibiotic (trade name Erythrocin or E-Mycin or Ethril or Ilosone or Pediamycin) obtained from the actinomycete Streptomyces erythreus; effective against many Gram-positive bacteria and some Gram-negative Synonym(s) erythromycin Erythrocin E-Mycin Ethril Ilosone Pediamycin