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
Broad-spectrum antibiotic that lists the susceptibility of community-acquired and hospital-acquired bacteria is helpful in guiding empiric therapy. Many professional organizations (for example, the Infectious Disease Society of America) publish guidelines for empiric antibiotic therapy, as do hospitals, with their choices tailored for their specific resistance patterns. Many of these guidelines also offer guidance on antibiotic dose and duration of therapy. Once a specific species has been identified and its susceptibilities determined, antibiotics can be "narrowed" to a medication which targets a more specific range of bacteria. If no specific species are identified, patients may continue on the empiric regimen. There are an