Properties and potential of ertapenem

Ertapenem is a carbapenem that shares the activity of imipenem and meropenem against most species, but is less active against non-fermenters. Activity is retained against most strains with AmpC and extended-spectrum beta-lactamases, although resistance can arise if these enzymes are combined with extreme impermeability. Resistance can also be caused by IMP, VIM, KPC and NMC carbapenemases, but again, co-requires impermeability. Although the spread of carbapenemases in the future is a concern, they are currently very rare. Given as a 1 g intravenous (iv) infusion once daily, ertapenem has a plasma half-life of similar to4 h in healthy volunteers, and a C-max of 155 mg/L and 13 mg/L for total and free drug, respectively. Excretion is largely renal, divided equally between native drug and an open-ring derivative. Trials show equivalence to piperacillin/tazobactam or ceftriaxone in (a) intra-abdominal infections, (b) community-acquired pneumonia, (c) acute pelvic infections, (d) skin and skin structure infections and (e) complicated urinary tract infections. The USA licence grants all these five indications; the EU licence grants the first three. Further potential uses include home iv therapy, directed therapy against Enterobacteriaceae with AmpC or extended-spectrum cephalosporinases, and tentatively, surgical prophylaxis. Widening the usage of carbapenems raises public health concerns, somewhat allayed by the continued rarity of carbapenemases after 17 years of imipenem use, and by the fact that carbapenemases occur mostly in non-fermenters outside the spectrum of ertapenem, and co-require impermeability to confer resistance in Enterobacteriaceae. Nevertheless, if ertapenem is to be used widely, its effects on the resistance ecology need to be monitored carefully.