Will amoxicillin-clavulanate (amoxi-clav) cover Staphylococcus aureus and other Gram-negative bacilli?

Amoxicillin-Clavulanate Coverage for Staphylococcus aureus and Gram-Negative Bacilli

Yes, amoxicillin-clavulanate effectively covers Staphylococcus aureus (methicillin-susceptible strains) and many gram-negative bacilli, making it an excellent broad-spectrum antibiotic choice for mixed infections. 1

Coverage for Staphylococcus aureus

• Amoxicillin-clavulanate provides excellent coverage against methicillin-susceptible Staphylococcus aureus (MSSA) 1, 2
• The addition of clavulanic acid to amoxicillin extends its spectrum to include penicillinase-producing strains of S. aureus that would otherwise be resistant to amoxicillin alone 1, 3
• Clinical studies have demonstrated that amoxicillin-clavulanate is effective for treating skin and skin structure infections caused by beta-lactamase-producing isolates of S. aureus 1, 4
• It is important to note that amoxicillin-clavulanate is NOT recommended for methicillin-resistant S. aureus (MRSA) infections 5

Coverage for Gram-Negative Bacilli

• Amoxicillin-clavulanate is effective against several important gram-negative bacilli, including: 1

  • Haemophilus influenzae (including beta-lactamase producing strains)
  • Escherichia coli (beta-lactamase producing strains)
  • Klebsiella species
  • Moraxella catarrhalis
  • Enterobacter species (in urinary tract infections)
  • Proteus mirabilis and Proteus vulgaris 3, 4

• The FDA specifically indicates amoxicillin-clavulanate for infections caused by beta-lactamase-producing isolates of these gram-negative organisms 1

Limitations of Coverage

• Amoxicillin-clavulanate has limited activity against certain gram-negative bacilli, including: 4

  • Pseudomonas aeruginosa
  • Serratia marcescens
  • Some Enterobacter species (particularly in non-urinary infections)
  • Stenotrophomonas maltophilia
  • Burkholderia cepacia

• The beta-lactamases produced by Enterobacter species, Proteus morganii, and Serratia marcescens are less susceptible to inhibition by clavulanic acid, making these organisms often resistant to amoxicillin-clavulanate 3

Clinical Applications

• Amoxicillin-clavulanate is FDA-approved for treating: 1

  • Skin and skin structure infections caused by beta-lactamase-producing S. aureus, E. coli, and Klebsiella species
  • Lower respiratory tract infections caused by beta-lactamase-producing H. influenzae and M. catarrhalis
  • Sinusitis and acute otitis media caused by beta-lactamase-producing organisms
  • Urinary tract infections caused by beta-lactamase-producing E. coli, Klebsiella species, and Enterobacter species

• For mixed infections where both S. aureus and gram-negative bacilli are suspected, amoxicillin-clavulanate is often an excellent empiric choice 6

Dosing Considerations

• For most infections, standard dosing is appropriate, but for more severe infections or those with suspected resistant organisms, high-dose amoxicillin-clavulanate (2g orally twice daily or 90 mg/kg/day orally twice daily) may be preferred 6

• When treating infections where S. aureus is a concern, the WHO Expert Committee recommends amoxicillin-clavulanate as a first-line treatment for mild to moderate infections 6

Remember that while amoxicillin-clavulanate has good coverage against MSSA and many gram-negative bacilli, it should not be used when susceptibility testing shows susceptibility to amoxicillin alone, indicating no beta-lactamase production 1. This judicious use helps prevent unnecessary antibiotic resistance development.