The bactericidal activity of ertapenem results from the inhibition of cell wall synthesis and is mediated through ertapenem binding to penicillin binding proteins (PBPs). In Escherichia coli, it has strong affinity toward PBPs 1a, 1b, 2, 3, 4 and 5 with preference for PBPs 2 and 3. Ertapenem is stable against hydrolysis by a variety of beta-lactamases, including penicillinases, and cephalosporinases and extended spectrum beta-lactamases. Ertapenem is hydrolyzed by metallo-beta-lactamases.

Ertapenem has in vitro activity against gram-positive and gram-negative aerobic and anaerobic bacteria.

The major metabolite is the inactive ring-opened derivative formed by hydrolysis of the β-lactam ring. Ertapenem did not inhibit metabolism mediated by cytochrome P450 (CYP) isoforms 1A2, 2C9, 2C19, 2D6, 2E1, or 3A4 when evaluated by in vitro studies in human liver microsomes. Ertapenem is neither a substrate nor an inhibitor of P-glycoprotein or cytochrome P450 enzymes; significant drug interactions between ertapenem and drugs handled by these systems are not expected [PMID: 15150180]

Nix DE, Majumdar AK, DiNubile MJ: Pharmacokinetics and pharmacodynamics of ertapenem: an overview for clinicians. J Antimicrob Chemother. 2004 Jun;53 Suppl 2:ii23-8. [PubMed:15150180