'Antibiotic literally means "anti-life." Any drug that's anti-life is undoubtedly going to cause varying degrees of harm or even death in some cases. "When once you interfere with the order of nature, there is no knowing where the results will end." -- Herbert Spencer, 19th Century British philosopher/biologist.
Margaret Riley, Ph.D. professor of biology at the University of Massachusetts, Amherst, considers taking a course of antibiotics analogous to ingesting a hydrogen bomb that indiscriminately kills everything in its path.'