ERYTHROMYCIN is derived from a strain of Streptomyces and belongs to the macrolide family of antibiotics which includes triacetyloleandomycin. Erythromycin was introduced in 1952. Erythromycin propionate was introduced in September, 1958. Its lauryl sulfate salt has been named erythromycin estolate. The manufacturer estimates that some 15 million courses of therapy with this drug have been given since its introduction, with only 33 cases of jaundice having been reported as directly or indirectly attributable to the drug. Kuder, in reviewing 20,525 cases, noted that erythromycin propionate caused some type of gastrointestinal symptomatology in 5.7% of patients, whereas the lauryl sulfate salt of this drug (erythromycin estolate) caused only 2% to have gastrointestinal symptoms. In both instances, the gastrointestinal symptoms constituted the major side effects, with nausea leading the list. No jaundice or hepatitis was reported in this series. He also observed that of 69 patients less than one month of age