In the case of tb, for example, there are 16,000 varients of the bacteria. There are bacteria that are anaerobic and those that are not. There
gram positive and
gram negative. As for the side effects file a drug reaction form at the FDA site. There are many different reactions to what are similar antibiotics. For example many people tolerate Cipro, a fluoroqinalone and cannot tolerate Levaquin, a similarly structed antibiotic.