Antibiotic brand names include Keflex, Zithromax, Levaquin, Bactrim and Tobrex. Each of these brands represents a major antibiotic drug class. While there are over 100 different brands of antibiotics, all of them come from seven drug classes.
The seven main antibiotic drug classes are aminoglycosides, penicillins, macrolides, cephalosporins, fluoroquinolones, tetracyclines and sulfonamides. Keflex is a cephalosporin, Zithromax is a macrolide, and Levaquin is a fluoroquinolone. Bactrim is a sulfonamide, and Tobrex is an aminoglycoside. Penicillins and tetracyclines are largely off-patent and are generally referred to by their generic names.
Antibiotic drug classes are determined by the organic structures of the compounds in that class, by the organisms the antibiotic was either cultured or synthesized from, or both. For example, cephalosporin antibiotics are derived from the fungus Cephalosporium acremonium. Macrolide antibiotics are produced by actinomycete bacteria of the genus Streptomyces. They also exhibit a lactone ring structure comprised of at least 12 members and linked by at least one sugar.
Antibiotics are chosen for a given bacterial infection based on several factors. These include the types of pathogens that normally cause a particular infection, whether or not a particular pathogen takes a stain in the laboratory, and whether a particular organism is sensitive to a given drug class. Additionally, cost, side effects and dosing schedule may be considered.