Clinical relevance of laboratory susceptibility data

The breakpoints for macrolides proposed by various organisation differ. In vitro studies may not give a true measure of breakpoints as culture conditions are not necessarily analogous to the in vivo situation. The effects of pH, carbon dioxide and culture media can affect the minimum inhibitory concentrations of macrolides; the extent of these effects varies for the different agents. Microbiological efficacy should ideally be proven under clinical conditions, but this is not always feasible. The breakpoints of macrolides should be reviewed taking into account the site of infection.