Macrolides currently account for 10% to 15% of the worldwide oral antibiotic market.' Erythromycin, the first macrolide antibiotic, was discovered in 1952 from a strain of Streptomyces erythreus obtained from soil samples in the Phillipines. Originally, erythromycin was marketed as an alternative to penicillin because of its activity against gram-positive organisms such as staphylococci, pneumococci, and streptococci. Subsequently, its clinical use broadened to include species of Mycoplasma, Legionella, Campylobacter, and Chlamydia. Although several other macrolides have been marketed in countries other than the United States, they have failed to achieve erythromycin's widespread use. Unfortunately, erythromycin suffers from several drawbacks, including gastrointestinal side effects, a short serum elimination half-life, and only borderline in vitro activity against common gram-negative respiratory pathogens such as Haemophilus influenzae.