Is susceptibility to ampicillin indicative of susceptibility to Augmentin (amoxicillin-clavulanate)?

From the Guidelines

If a bacterium is susceptible to ampicillin, it is likely to be susceptible to Augmentin (amoxicillin-clavulanate) as well, due to the similar mechanism of action and the addition of a beta-lactamase inhibitor in Augmentin. The provided evidence from the 2015 ESC guidelines for the management of infective endocarditis 1 supports the use of amoxicillin or ampicillin in certain cases, and notes that beta-lactam resistance due to beta-lactamase production can be addressed by using ampicillin-sulbactam or amoxicillin-clavulanate. Key points to consider include:

• The mechanism of action of ampicillin and amoxicillin are closely related, with amoxicillin being protected from beta-lactamase degradation by clavulanic acid in Augmentin.
• Bacteria susceptible to ampicillin are likely to be susceptible to Augmentin, unless they have resistance mechanisms other than beta-lactamase production.
• Specific susceptibility testing is recommended in clinical practice to ensure appropriate antibiotic selection for serious infections, as guided by the principles outlined in the 2015 ESC guidelines 1. The use of Augmentin as an alternative to ampicillin in certain infections is supported by its broader spectrum of activity, which includes coverage against some ampicillin-resistant strains that produce beta-lactamases, as implied by the discussion on beta-lactam resistance in the guidelines 1.

From the FDA Drug Label

The FDA drug label does not answer the question.

From the Research

Susceptibility to Ampicillin and Augmentin

• Susceptibility to ampicillin is not always indicative of susceptibility to Augmentin (amoxicillin-clavulanate) 2
• The study found that Augmentin is active against penicillinase-producing Staphylococci susceptible to methicillin, but methicillin-resistant strains are also resistant to Augmentin 2
• Enterobacteriaceae can be divided into five main phenotypes based on their susceptibility to amoxicillin, carbenicillin, and cefalotin, and Augmentin is effective against some of these phenotypes, particularly those that are penicillinase producers 2

Beta-Lactamase Inhibitors and Antibiotic Resistance

• Beta-lactamase inhibitors, such as sulbactam, can restore or expand the activity of older beta-lactam antibiotics against bacterial infections 3
• The combination of sulbactam and ampicillin is effective against polymicrobial aerobic or anaerobic infections and uncomplicated gonorrhea, but not against pseudomonal infections 3
• The use of beta-lactamase inhibitors can help to overcome antibiotic resistance, but the risk of emergent resistance remains a concern 4

Alternative Antibiotic Therapies

• Alternative antibiotic therapies, such as piperacillin/tazobactam, cefepime, or trimethoprim/sulfamethoxazole, may be effective against inducible AmpC β-lactamase-producing Gram-negative bacilli 4
• The combination of sulbactam and ampicillin has been shown to be effective against animal isolates of Pasteurella, Haemophilus, and Staphylococcus, and may be a useful alternative therapy in certain cases 5