Article: Ertapenem

Ertapenem is a carbapenem marketed by Merck as Invanz®. It is structurally very similar to meropenem in that it possess a 1-β-methyl group.

Indications

Ertapenem is designed to be effective against Gram negative bacteria. It is not active against MRSA, ampicillin-resistant enterococci, Pseudomonas aeruginosa or Acinetobacter species. Ertapenem also has clinically useful activity against anaerobic bacteria.

Ertapenem is marketed by Merck as a first-line treatment for community-acquired infections. It should not be used as empirical treatment for hospital-acquired infections because of its lack of activity against Pseudomonas aeruginosa. In practice, it is reserved primarily for use against ESBL-producing and high level AmpC-producing Gram-negative bacteria.

Dosage

Ertapenem is dosed as 1g given by intravenous injection over 30 minutes, or 1g diluted with 3.2ml of 1% lidnocaine given intramuscularly. There is no oral preparation of ertapenem available. Ertapenem cannot be mixed with glucose.

The marketing slogan for ertapenem is "The Power of One", because the dose is one gram, once a day.

Pharmacology

Unlike imipenem and meropenem, ertapenem is highly protein bound, which explains its long half life (4 hours).

Ertapenem is excreted primarily (80%) by the kidneys. Metabolism by the liver is not clinically important and does not affect dosing.

Patients on haemodialysis should be given ertapenem at least 6 hours before dialysis. If it is given less than six hours before dialysis, then the patient should be given an additional dose of 150mg IV after dialysis. Ideally, patients on haemodialysis should be given ertapenem immediately following dialysis.

Side effects

There are few adverse effects of ertapenem. The only absolute contra-indication is a previous anaphylactic reaction to ertapenem or other β-lactam antibiotic. There are no studies done in pregnant women, so the manufacturers cannot comment on its safety in pregnancy. There are no studies in children, and therefore there is no license for use in children aged under 18 years of age.

Use of all antibiotics is associated with increased rates of resistance (although carbapenem resistance is currently rare). There is particular worry that although ertapenem has no clinically useful activity against Pseudomonas aeruginosa, widespread use of ertapenem could still lead to increased carbapenem resistance in Pseudomonas (Livermore 2005).

Like all antibiotics, C. difficile colitis has been associated with its use.