What bacteria does amoxicillin-clavulanate (amox-clav) cover that amoxicillin does not?

Amoxicillin-Clavulanate Coverage Compared to Amoxicillin Alone

Amoxicillin-clavulanate covers beta-lactamase-producing bacteria that amoxicillin alone cannot treat, specifically including beta-lactamase-producing strains of Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus, Escherichia coli, Klebsiella species, and Enterobacter species. 1

Mechanism of Action

The key difference between these two antibiotics lies in the addition of clavulanic acid:

• Amoxicillin alone: A penicillin-class antibiotic that inhibits bacterial cell wall synthesis
• Clavulanic acid: Functions as a beta-lactamase inhibitor that irreversibly binds to bacterial beta-lactamases, preventing these enzymes from destroying amoxicillin 2

This "suicide inhibitor" mechanism allows amoxicillin to remain active against bacteria that would otherwise inactivate it through beta-lactamase production.

Specific Organisms Covered by Amoxicillin-Clavulanate But Not Amoxicillin

According to FDA labeling and clinical guidelines, amoxicillin-clavulanate extends coverage to include:

1. Respiratory pathogens:

   • Beta-lactamase-producing Haemophilus influenzae
   • Beta-lactamase-producing Moraxella catarrhalis 1

2. Skin and soft tissue pathogens:

   • Beta-lactamase-producing Staphylococcus aureus
   • Beta-lactamase-producing Escherichia coli
   • Beta-lactamase-producing Klebsiella species 1

3. Urinary tract pathogens:

   • Beta-lactamase-producing Escherichia coli
   • Beta-lactamase-producing Klebsiella species
   • Beta-lactamase-producing Enterobacter species 1

4. Anaerobes:

   • Bacteroides fragilis (implied by research evidence) 3

Clinical Applications

The addition of clavulanate becomes particularly important in:

• Sinusitis: For patients who don't respond to amoxicillin, high-dose amoxicillin-clavulanate is recommended to cover beta-lactamase-producing H. influenzae and M. catarrhalis 4

• Acute otitis media: High-dose amoxicillin-clavulanate is recommended for patients who have taken amoxicillin in the previous 30 days, those with concurrent conjunctivitis, or when coverage for M. catarrhalis is desired 4

• Respiratory tract infections: In regions with high incidence of antibiotic resistance, amoxicillin-clavulanate provides coverage against resistant bacteria that amoxicillin alone cannot treat 4

Important Considerations

• Amoxicillin-clavulanate should not be used when susceptibility testing shows susceptibility to amoxicillin alone (indicating no beta-lactamase production) 1

• Gastrointestinal side effects, particularly diarrhea, are more common with amoxicillin-clavulanate than with amoxicillin alone, especially when clavulanate dose exceeds approximately 10 mg/kg per day 2

• Twice-daily dosing has significantly fewer gastrointestinal side effects compared to three-times-daily dosing 2

• For resistant infections, high-dose formulations may be necessary to overcome resistant pathogens in respiratory infections 5

In summary, the addition of clavulanate to amoxicillin significantly expands its spectrum to include beta-lactamase-producing organisms that would otherwise be resistant to amoxicillin alone, making it particularly valuable for treating infections where these resistant organisms are suspected or confirmed.