Oleandomycin is a macrolide antibiotic, which was first described under the designation P.A.105 by Sobin, English, and Celmer (1954-5). Later it appeared on the market under three names and in two forms: as pure oleandomycin ("matromycin," Pfizer; "romicil," Hoffmann-La Roche) and as a mixture with twice its weight of tetracycline ("sigmamycin," Pfizer). Oleandomycin can be employed to inhibit the activities of bacteria responsible for causing infections in the upper respiratory tract much like Erythromycin can. Both can affect staphylococcus and enterococcus genera. Oleoandomycin is reported to inhibit most gram-positive bacteria, but has only a slight inhibiting effect on gram-negative bacteria, rickettsiae, and larger viruses. The spectrum of activity on micro-organisms is therefore wider than that of penicillin and streptomycin, but narrower than that of chloramphenicol and the tetracyclines. Oleandomycin is approved as a veterinary antibiotic in some countries. It has been approved as a swine and poultry antibiotic in the United States. However, it is currently only approved in the United States for production uses. Oleandomycin is a bacteriostatic agent. Like erythromycin, oleandomycin binds to the 50s subunit of bacterial ribosomes, inhibiting the completion of proteins vital to survival and replication. It interferes with translational activity but also with 50s subunit formation. However, unlike erythromycin and its effective synthetic derivatives, it lacks a 12-hydroxyl group and a 3-methoxy group. This change in structure may adversely affect its interactions with 50S structures and explain why it is a less powerful antibiotic.