The term "broad spectrum antibiotics" was originally used to designate antibiotics that were effective against both gram-positive and gram-negative bacteria, in contrast to penicillin, which is effective chiefly against gram-positive organisms, and streptomycin, which is active primarily against gram-negative bacteria. The broad spectrum antibiotics have an antimicrobial spectrum which includes some gram-positive and some gram-negative organisms, as well as certain rickettsiae, larger viruses, protozoa, and pleuropneumonia-like organisms. Although the antimicrobial spectra of other antibiotics vary in their breadth of coverage, this article will be limited to a discussion of the tetracyclines and chloramphenicol.
There are four basic tetracycline homologues. The first two were prepared entirely by fermentation methods. Chlortetracycline hydrochloride was isolated from Streptomyces aureofaciens by Duggar1 in 1948 and oxytetracycline, produced by S rimosus, was introduced in 1950. Tetracycline was prepared by catalytic hydrogenation of the chlorine radical and introduced for clinical use in 1953. Demethylchlortetracycline,