Is meropenem safe to use in patients with a known penicillin allergy?

Meropenem Safety in Patients with Penicillin Allergy

Meropenem can be safely administered to patients with a known penicillin allergy, regardless of severity or time since the index reaction, without prior allergy testing. 1, 2

Cross-reactivity Between Penicillins and Carbapenems

• Carbapenems have molecular structures sufficiently dissimilar from penicillins, resulting in a very low risk of cross-allergy 2
• The risk of cross-reactivity between penicillins and any carbapenem is only 0.87% (95% CI: 0.32%-2.32%) 2
• Multiple guidelines strongly recommend that patients with suspected immediate-type penicillin allergy can receive any carbapenem without prior allergy testing 1
• This recommendation applies regardless of:
  • Severity of the previous reaction 1
  • Time elapsed since the index reaction 1
  • Whether the allergy is confirmed or just suspected 2

Clinical Evidence Supporting Safety

• Prospective studies have demonstrated extremely low rates of cross-reactivity:
  • Only 0.9% of patients with documented penicillin allergy showed positive skin tests to meropenem 3
  • In a study of 110 patients with reported penicillin allergies (including 51 with anaphylactic reactions), none experienced allergic reactions when given meropenem 4
  • Among 108 children with documented IgE-mediated penicillin hypersensitivity, only one (0.9%) had a positive skin test to meropenem, and all others tolerated challenges 5

Important Considerations and Precautions

• While meropenem is contraindicated in patients with known hypersensitivity to carbapenems or who have demonstrated anaphylactic reactions to beta-lactams 6, this does not apply to patients with penicillin allergy alone
• The FDA label acknowledges that hypersensitivity reactions can occur and recommends inquiring about previous reactions to penicillins and other beta-lactams 6, but does not contraindicate use in penicillin-allergic patients
• Some older studies suggested higher cross-reactivity rates (up to 9.2% in one retrospective review 7), but more recent and rigorous prospective studies consistently show rates below 1% 4, 5, 3

Practical Approach

• Document the nature of the previous penicillin reaction 2
• Proceed with meropenem administration without prior testing 1, 2
• Monitor for potential hypersensitivity reactions during the first dose, especially in patients with a history of severe reactions 2
• For patients with non-severe delayed-type penicillin allergy, carbapenems can be administered without special precautions 1

Conclusion

The current evidence strongly supports the safety of meropenem in patients with penicillin allergy. The Dutch Working Party on Antibiotic Policy (SWAB) guidelines explicitly recommend that patients with suspected immediate-type penicillin allergy can receive any carbapenem without prior allergy testing 1. This is supported by multiple prospective clinical studies showing cross-reactivity rates below 1% 4, 5, 3.