Unasyn (Ampicillin-Sulbactam) Coverage
No, Unasyn does NOT provide coverage for Pseudomonas aeruginosa, but it DOES provide excellent coverage for anaerobes.
Pseudomonas Coverage
Ampicillin-sulbactam has no activity against Pseudomonas aeruginosa and should never be relied upon for anti-pseudomonal coverage. 1, 2, 3
- Research demonstrates that P. aeruginosa isolates show 82-100% resistance to ampicillin-sulbactam across respiratory, urinary, and skin infections 3
- Clinical failures have been documented specifically when Pseudomonas species were isolated in patients treated with ampicillin-sulbactam for perforated appendicitis 4
- The FDA label for ampicillin-sulbactam does not include Pseudomonas in its spectrum of activity 1
When Pseudomonas Coverage IS Needed
If you need anti-pseudomonal coverage, you must use:
- Piperacillin-tazobactam (specifically recommended by IDSA for diabetic foot infections when Pseudomonas suspected) 5, 6
- Cefepime, ceftazidime, or carbapenems (imipenem, meropenem) 5, 6
- These agents should be combined with vancomycin if MRSA coverage is also required 5, 6
Anaerobic Coverage
Ampicillin-sulbactam provides excellent coverage for anaerobic organisms, including Bacteroides fragilis. 1, 2, 7
- The FDA label specifically indicates efficacy against beta-lactamase producing strains of Bacteroides fragilis and other Bacteroides species 1
- IDSA guidelines list ampicillin-sulbactam as an appropriate choice for moderate-to-severe diabetic foot infections when anaerobic coverage is needed 5
- In vitro studies show ampicillin-sulbactam inhibits almost all anaerobic isolates at therapeutic concentrations 7
- Clinical trials demonstrate effectiveness against mixed aerobic-anaerobic infections 8
Clinical Indications for Unasyn
Ampicillin-sulbactam is appropriate for:
- Intra-abdominal infections with anaerobic involvement 5, 1
- Diabetic foot infections (moderate severity) where anaerobes are suspected but Pseudomonas is unlikely 5
- Skin and soft tissue infections caused by beta-lactamase producing organisms 1
- Gynecological infections with anaerobic pathogens 1
Critical Pitfall to Avoid
Do not use ampicillin-sulbactam empirically when:
- Pseudomonas risk factors are present (warm climate, frequent water exposure, healthcare-associated infection, high local prevalence) 5
- The patient has failed prior antibiotic therapy 5
- Severe or life-threatening infection where broader coverage is mandatory 5
The combination provides adequate gram-positive (including MSSA), some gram-negative (Enterobacteriaceae), and anaerobic coverage, but completely lacks anti-pseudomonal activity 1, 2.