Penicillins
Matt Krantz, MD
Assistant Professor of Medicine
Vanderbilt University Medical Center
Disclosures & Disclaimer
- Funding: Supported by the National Institutes of Health (NIH) under Award Number K08 AI185260 and the AAAAI Foundation.
- Educational Use: These materials are intended for research and educational purposes only.
- Work in Progress: This is an actively evolving resource; summaries reflect current lab review and may be updated as new data emerges.
- Views Are My Own
Core Concepts
What percent of the US population reports an allergy to penicillin?
Approximately 10% of the US population reports an allergy to penicillin.
What percentage of reported penicillin allergies are clinically significant?
Less than 5% are clinically significant immediate or delayed immune-mediated drug reactions.
Over 95% of patients are actually tolerant because:
- The index reaction was likely a benign delayed rash.
- IgE-mediated allergy wanes over time (80% tolerance after a decade).
- The reaction may have been an intolerance or caused by the underlying infection.
What infections are individuals with a penicillin allergy label at higher risk of developing?
These individuals are more likely to receive broad-spectrum antibiotics, increasing the risk for:
- Antimicrobial resistance (MRSA, VRE)
- C. difficile infection
- Surgical site infections (due to non-beta-lactam perioperative prophylaxis)
What infection-related drug interaction is associated with individuals developing a maculopapular rash when receiving an aminopenicillin?
Epstein-Barr virus.
What percent of penicillin administrations result in a reaction that could be consistent with a hypersensitivity reaction, most often a rash, that could also be nonallergic?
About 0.5% to 2.0%
What is a potential hypothesis for the decreasing rate of IgE-mediated penicillin allergies?
Potentially due to the decrease in use of parenteral penicillins in the outpatient setting.1
What is the negative predictive value of penicillin skin testing?
The NPV of penicillin skin testing is > 95% when performed with only benzylpenicilloyl polylysine plus penicillin G or with benzylpenicilloyl polylysine plus full panel of minor derterminants.
Penicillin Skin Testing
| Reagent | Description |
|---|---|
| Penicilloyl polylysine (PrePen®) | Major antigenic determinant (95% of penicillin degradation). Complexed with polylysine to constitute a multivalent skin test reagent. Acts as the carrier for the penicilloyl hapten in vivo. |
| Minor determinant mixture (MDM) | Contains Penicillin G, penicilloate, and penilloate. Not commercially available in the US. |
| Penicillin G | Also called benzylpenicillin. |
| Ampicillin | Differs from Penicillin G by the presence of an amino group (-NH2). |