Can Ertapenem Be Used in Patients with Amoxicillin Allergy?
Yes, ertapenem can be safely administered to patients with amoxicillin allergy without prior allergy testing, regardless of the severity or timing of the previous reaction. 1
Evidence for Safety
The cross-reactivity between penicillins (including amoxicillin) and carbapenems is extremely low:
- The risk of cross-reactivity between penicillins and any carbapenem is only 0.87% (95% CI: 0.32%-2.32%) 2, 1
- Carbapenems have molecular structures sufficiently dissimilar from penicillins, resulting in minimal cross-allergy risk 1
- A prospective study of 211 patients with skin test-confirmed penicillin allergy demonstrated that all tolerated carbapenems 2
Clinical Recommendations
Ertapenem can be administered without prior allergy testing in patients with amoxicillin allergy, whether the allergy is confirmed or suspected, severe or non-severe, immediate or delayed-type 1:
- This applies regardless of time elapsed since the index reaction 2, 1
- No graded challenge or pretreatment skin testing is required 2, 1
- Patients with non-severe, delayed-type penicillin allergy can receive any carbapenem without prior testing 2
Important Caveats
FDA Warning on Hypersensitivity
The FDA label for ertapenem states that serious and occasionally fatal hypersensitivity (anaphylactic) reactions have been reported in patients receiving beta-lactams 3:
- These reactions are more likely in individuals with a history of sensitivity to multiple allergens 3
- There have been reports of individuals with penicillin hypersensitivity experiencing severe reactions when treated with another beta-lactam 3
- If an allergic reaction occurs, discontinue ertapenem immediately 3
Practical Approach
Despite the FDA's cautionary language, current guideline evidence strongly supports safe use:
- Document the nature of the previous amoxicillin reaction before administering ertapenem 1
- Consider administering the first dose in a monitored clinical setting if there are specific concerns about a severe previous reaction 1
- Ensure emergency medications are available, though reaction risk is extremely low 1
- The practice of routinely avoiding carbapenems in patients with beta-lactam allergy should be abandoned given the very low cross-reactivity rate 4
Special Considerations for Perioperative Use
When using ertapenem for perioperative prophylaxis in penicillin-allergic patients:
- Exercise caution in patients with suspected immediate hypersensitivity to beta-lactams 2
- Ertapenem is preferred over meropenem/imipenem due to single administration and antimicrobial stewardship considerations 2
- Use alternatives if multiple drug allergies are present or if patient anxiety is significant 2