The macrolides were introduced in the early 1950s; the first member of the group was erythromycin. Erythromycin is considered to be among the safest of all antibiotics that are currently available. Today however, there is less use of erythromycin because this drug has many drug interactions, microbial resistance has developed to erythromycin, and newer macrolides have been created. Currently there are six members of this group with azithromycin (Zithromax). clarithromycin (Biaxin) and telithromycin (Ketek) being the newest members. The macrolides can be bacteriostatic or bactericidal depending on their concentration in susceptible bacteria and they are also considered to be broad-spectrum. Erythromycin has a spectrum of use similar to penicillin and is often used with clients who are allergic to penicillin. There are a number of bacterial infections in which the macrolides are the first line of treatment. The macrolides are well distributed to most body tissues and fluids except for cerebral spinal fluid (CSF) and they do cross the placenta. They are excreted by the liver.