Ertapenem, the first of a new group of carbapenems

β-Lactam antimicrobials have been widely prescribed to treat serious infections for nearly 60 years owing to their excellent efficacy, safety and tolerability profiles. Among the many different structurally dis- tinct classes of β-lactams, the carbapenem class, while sharing these general β-lactam features, is regarded as the class that is most potent and that has the widest spectrum of antimicrobial activity. At the time that the carbapenems were last reviewed in this journal,1 imipenem and meropenem were the only carbapenems that were available in the majority of the world. Since then ertapenem (formerly MK-0826), a new long-acting, parenteral carbapenem (Figure 1), has received regulatory approval in the United States (November 2001) and the European Union (April 2002). The introduction of ertapenem should make us reconsider how we think of the carbapenems. Ertapenem is sufficiently different in some key attributes from imipenem and meropenem that we can no longer consider all available carbapenems as if they were a homogeneous class. In order to consider the appropriate role of ertapenem in the current antimicrobial armamentarium, this article reviews the key attributes of ertapenem and the other carbapenems and proposes a classification scheme for the carbapenem class; imipenem and mero- penem will be discussed first.1,2