Antimicrobial agents: the old and the new.

Although there are many new antimicrobial agents, many of the old antibiotics are still useful in the treatment of infections, particularly those in the community. Antimicrobial resistance patterns and special pharmacologic properties should influence the selection of newer antimicrobial agents. Change from parenteral therapy to oral therapy should increase to avoid the complications of intravenous therapy and to reduce hospital costs. Older antibiotics that are less costly should be used when the etiology and susceptibility of infecting pathogens are known. There will continue to be new antibiotics produced. Understanding the microbiologic and pharmacologic advantages of the new agents compared with older agents is essential if the new agents are to be used properly and not destroyed by inappropriate use.