Antimicrobial Coverage of Unasyn (Ampicillin-Sulbactam)
Unasyn (ampicillin-sulbactam) covers a broad spectrum of bacteria including beta-lactamase producing organisms, Gram-positive cocci, Gram-negative bacilli, and anaerobes, making it effective for mixed infections such as intra-abdominal, skin/soft tissue, and gynecological infections. 1
Mechanism of Action
- Ampicillin acts by inhibiting cell wall mucopeptide biosynthesis during bacterial multiplication 1
- Sulbactam irreversibly inhibits a wide range of beta-lactamases, effectively extending ampicillin's spectrum to include beta-lactamase producing strains 1
- The combination provides both bactericidal activity and protection against enzymatic degradation 1
Gram-Positive Coverage
- Staphylococcus aureus (beta-lactamase producing strains) 1
- Streptococcus species (including S. pneumoniae, S. pyogenes, S. viridans) 1
- Enterococcus faecalis 1
- Peptostreptococcus species (anaerobic) 1
- Clostridium species (anaerobic) 1
Gram-Negative Coverage
- Escherichia coli (beta-lactamase and non-beta-lactamase producing) 1
- Klebsiella species (including K. pneumoniae) 1
- Proteus mirabilis (beta-lactamase and non-beta-lactamase producing) 1
- Proteus vulgaris 1
- Enterobacter species 1
- Acinetobacter calcoaceticus 1
- Bacteroides species (including B. fragilis) 1
- Haemophilus influenzae (beta-lactamase and non-beta-lactamase producing) 1
- Moraxella catarrhalis 1
- Neisseria gonorrhoeae 1
- Providencia species (P. rettgeri, P. stuartii) 1
- Morganella morganii 1
Clinical Applications
- Skin and soft tissue infections caused by beta-lactamase producing organisms 1, 2
- Intra-abdominal infections 1, 2
- Gynecological infections 1
- Mixed infections where both aerobic and anaerobic coverage is needed 2
- Animal and human bite infections 2
- Necrotizing fasciitis (as part of combination therapy) 2
- Diabetic foot infections (moderate to severe) 2
Important Clinical Considerations
- Unasyn is not recommended for routine use in community-acquired intra-abdominal infections due to high rates of resistance among community-acquired E. coli 2
- It is particularly useful for mixed infections requiring both aerobic and anaerobic coverage 2
- For necrotizing fasciitis, it is often combined with clindamycin and ciprofloxacin for optimal coverage 2
- In HACEK microorganism infections (endocarditis), ampicillin-sulbactam is an effective alternative to ceftriaxone 2
Limitations of Coverage
- Not effective against methicillin-resistant Staphylococcus aureus (MRSA) 2
- Limited activity against Pseudomonas aeruginosa 3
- Not effective against extended-spectrum beta-lactamase (ESBL) producing organisms 2
- Not recommended for empiric use in healthcare-associated infections without local susceptibility data 2
Dosing Considerations
- Typical adult dosing is 1.5-3.0 g IV every 6-8 hours 2
- Dosage adjustment required in renal impairment 1
- For severe infections, higher doses may be required 2
Understanding the antimicrobial spectrum of Unasyn is crucial for appropriate prescribing, as resistance patterns continue to evolve and vary by geographic location. Local antibiograms should guide empiric therapy decisions when possible.