Launched commercially in 1952, Erythromycin is an antibiotic used for the treatment of a number of bacterial infections, including respiratory tract infections, skin infections, chlamydia infections, pelvic inflammatory disease, and syphilis. It may also be used during pregnancy to prevent Group B streptococcal infection in the newborn, as well as to improve delayed stomach emptying. Basically, Erythromycin works by stopping bacteria from producing essential proteins. Of course, the bacteria cannot grow without these proteins, nor can they replicate and increase in numbers. As for the side effects of this medication, they include abdominal cramps, vomiting, and diarrhea. In fact, Erythromycin has more serious side effects that need to be taken into consideration such as Clostridium difficile colitis, liver problems, and allergic reactions. However, this antibiotic is generally safe in those who are allergic to penicillin. Erythromycin also appears to be safe to use during pregnancy. And while generally regarded as safe during breastfeeding, the use of Erythromycin by the mother during the first two weeks of life may increase the risk of pyloric stenosis in the baby.This risk also applies if taken directly by the baby during this age.