Discordant Results: Amoxicillin-Clavulanate and Ampicillin-Sulbactam

Discordant Results : Amoxicillin-Clavulanate and Ampicillin-Sulbactam

A with a drained intra-abdominal abscess was sent with amoxicillin/clavulanate

An operative culture grows E. coli with this susceptibility:

Ampicillin = R
Amoxicillin/clavulanate = S
Ampicillin/sulbactam = R

Should antibiotics be changed?

How did others respond?

Reveal the answer

Best Answer

No, therapy is active ✅

Explanation: Discordant susceptibility between amoxicillin/clavulanate and ampicillin/sulbactam can be confusing. The short answer is TRUST the susceptibility report and that amoxicillin/clavulanate can be used.

But why might susceptibility differ? 🤔

Though both agents are an aminopenicillin + beta-lactamase inhibitor, 2️⃣ issues could result in discordant susceptibility:

1. Clavulanate is more potent & inhibits beta-lactamases sulbactam can’t.

2. Lab errors may result in overestimation of MICs for ampicillin/sulbactam.

Don’t let beta-lactamases baffle you!