What is the bacterial coverage of Unasyn (Ampicillin-Sulbactam)?

Bacterial Coverage of Unasyn (Ampicillin-Sulbactam)

Unasyn (ampicillin-sulbactam) provides broad-spectrum coverage against gram-positive, gram-negative, and anaerobic bacteria, including beta-lactamase producing organisms. The combination effectively extends ampicillin's spectrum by adding sulbactam, which irreversibly inhibits many clinically important beta-lactamases.

Spectrum of Activity

Gram-Positive Bacteria

• Staphylococcus species (including beta-lactamase producing strains)
  • Staphylococcus aureus (methicillin-susceptible)
  • Staphylococcus saprophyticus
• Streptococcus species
  • Streptococcus pneumoniae
  • Streptococcus pyogenes
  • Streptococcus viridans group
• Enterococcus faecalis

Gram-Negative Bacteria

• Haemophilus influenzae (beta-lactamase and non-beta-lactamase producing)
• Moraxella catarrhalis (formerly Branhamella catarrhalis)
• Escherichia coli (beta-lactamase and non-beta-lactamase producing)
• Klebsiella species
• Proteus species (mirabilis and vulgaris)
• Providencia species (rettgeri and stuartii)
• Morganella morganii
• Neisseria gonorrhoeae
• Acinetobacter species

Anaerobic Bacteria

• Bacteroides species, including Bacteroides fragilis
• Clostridium species
• Peptococcus species
• Peptostreptococcus species

Clinical Applications

Unasyn is particularly valuable in treating:

1. Mixed infections where both aerobic and anaerobic coverage is needed 1
2. Intra-abdominal infections 2
3. Skin and soft tissue infections, particularly animal and human bites 2
4. Gynecological infections including PID 2
5. Urogenital tract infections 3, 4

Important Considerations

• Unasyn does not cover MRSA, Pseudomonas aeruginosa, or extended-spectrum beta-lactamase (ESBL) producing organisms
• For serious infections, the typical dosage is 3g IV every 6 hours 2
• When treating polymicrobial infections, Unasyn provides better anaerobic coverage than cephalosporins alone 2
• For animal and human bites, Unasyn is specifically recommended for intravenous treatment 2

Advantages Over Other Agents

Ampicillin-sulbactam has several advantages over using metronidazole plus another agent:

1. It provides single-agent coverage for mixed infections
2. Unlike metronidazole, which requires combination with agents effective against gram-positive cocci 5, Unasyn inherently covers both gram-positive and anaerobic organisms
3. It demonstrates bactericidal activity against a wide range of pathogens 6

Limitations

• Not effective against ESBL-producing organisms
• Limited activity against Pseudomonas species
• Not effective against MRSA
• Pain at injection site is a common adverse effect with intramuscular administration 4

For empiric treatment of polymicrobial infections, Unasyn provides excellent broad-spectrum coverage and is particularly valuable when both aerobic and anaerobic pathogens are suspected.