Meropenem (Option D) is the Correct Answer
Meropenem possesses excellent activity against Pseudomonas aeruginosa and is specifically recommended as a first-line antipseudomonal carbapenem for severe infections, while the other options listed lack reliable antipseudomonal coverage. 1, 2
Why Meropenem is Effective Against Pseudomonas
Meropenem is a Group 2 carbapenem with documented activity against non-fermentative gram-negative bacilli including P. aeruginosa, distinguishing it from Group 1 carbapenems like ertapenem which lack this coverage 1
Clinical guidelines specifically recommend meropenem for P. aeruginosa infections at doses of 60-120 mg/kg/day divided in 3 doses (maximum 6g daily), with the ability to escalate to 3 × 2g in 3-hour infusions for severe cases 1, 2
Meropenem demonstrates superior in vitro activity against P. aeruginosa compared to imipenem, with only 4.2% resistance rates versus 12.5% for imipenem in North American isolates 3
The drug achieves bactericidal activity through stability against beta-lactamases and high affinity for essential penicillin-binding proteins, making it more active than imipenem against P. aeruginosa 4
Why the Other Options Are Incorrect
Ampicillin/Sulbactam (Option A)
- Has no clinically relevant activity against P. aeruginosa and is not mentioned in any guidelines for antipseudomonal coverage 1
Ertapenem (Option B)
- Ertapenem is a Group 1 carbapenem that explicitly lacks activity against P. aeruginosa and Enterococcus species, making it unsuitable for infections where Pseudomonas is a concern 1
- Guidelines specifically warn that ertapenem is "not active against P. aeruginosa infection" and should only be used for ESBL-producing Enterobacteriaceae 1
Ceftriaxone (Option C)
- Ceftriaxone is a third-generation cephalosporin without antipseudomonal activity 1
- Guidelines distinguish between non-antipseudomonal cephalosporins (like ceftriaxone) and antipseudomonal cephalosporins (like ceftazidime and cefepime) for empiric therapy decisions 1
Clinical Context for Meropenem Use
For severe P. aeruginosa infections, meropenem should be combined with a second antipseudomonal agent (ciprofloxacin or aminoglycoside) to prevent inadequate treatment and reduce resistance development 1
Meropenem ranks among the most active agents against P. aeruginosa globally, with 75.4-91% susceptibility rates depending on geographic region 5, 6
The drug maintains activity against many imipenem-resistant P. aeruginosa strains, with 43.8% of imipenem-resistant isolates remaining susceptible to meropenem 3
Common Pitfall to Avoid
Do not confuse all carbapenems as having equivalent coverage—ertapenem specifically lacks antipseudomonal activity despite being in the same drug class as meropenem, imipenem, and doripenem 1