What is the main limitation of ertapenem?

Ertapenem is a broad-spectrum carbapenem antibiotic known for its effectiveness against a variety of bacteria, but it has a notable limitation in that it does not provide coverage against Pseudomonas aeruginosa. This is significant because Pseudomonas is a common pathogen, particularly in neutropenic patients, those with cystic fibrosis, or patients with hospital-acquired infections. The inability to treat infections caused by Pseudomonas can limit the use of ertapenem in certain clinical scenarios where this organism is a possible causative agent.

The other options reflect common misconceptions regarding the spectrum of activity of ertapenem. For example, while it is known to cover anaerobes such as Bacteroides species, it also effectively covers a variety of gram-negative rods besides Pseudomonas. Additionally, ertapenem has shown good activity against Streptococcus species, making it suitable for infections caused by these organisms. Thus, the main limitation centers on its lack of efficacy against Pseudomonas, which can often guide a clinician's choice of antibiotic therapy in appropriate clinical settings.