Antibiotic improve treatment outcome as the combined effect of both antibiotics is better than their individual effect. Methicillin-resistant Staphylococcus aureus infections may be treated with a combination therapy of fusidic acid and rifampicin. Antibiotics used in combination may also be antagonistic and the combined effects of the two antibiotics may be less than if the individual antibiotic was given as part of a monotherapy. For example, chloramphenicol and tetracyclines are antagonists to penicillins and aminoglycosides. However, this can vary depending on the species of bacteria. In general, combinations of a bacteriostatic antibiotic and bactericidal antibiotic are antagonistic. Antibiotics are commonly classified
Antibiotic prophylaxis to the serious problem of superbugs (which are bred in antibiotic-rich environments) the Food and Drug Administration issued a guidance document in December 2013. The chief public health officer of Canada said four months later that "antibiotics should only be used in animals to treat infection rather than guard against disease or promote growth." The Canadian guidance document calls for "the prudent use of antibiotics in animal agriculture and a gradual phasing out of growth promoting drugs in feed and water over the three years" ending in 2017. Producers will no longer be allowed to continuously feed animals doses of