Penicillin is a powerful and commonly used antibiotic, but many people mistakenly believe they are allergic. Up to 90% of people who think they have a penicillin allergy might not be truly allergic! [1] This can be a problem because penicillin is often the most effective and affordable treatment for many infections.
New Tools for Identifying True Penicillin Allergies
Two new scoring systems are helping doctors differentiate true allergies from misunderstandings: PEN-FAST and PEN-FAST +.
PEN-FAST: A Quick and Easy Risk Assessment
Pen-Fast [penicillin allergy, within last five years, anaphylaxis/angioedema, severe cutaneous adverse reaction (SCAR), and treatment required for allergy episode] is a simple tool that considers three factors to assess your risk of a true penicillin allergy: [2]
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- Time since reaction: Reactions less than 5 years ago ( 2 points)
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- Reaction severity: Severe reactions like anaphylaxis, angioedema, or severe cutaneous adverse reaction (2 points)
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- Treatment needed: Reactions requiring treatment (1 point)
A low Pen-Fast score (less than 3 points) indicates you’re likely a good candidate for penicillin.
PEN-FAST +: Digging Deeper for More Accuracy
PEN-FAST is helpful for most cases, but it might miss some people with delayed skin reactions. PEN-FAST + adds two additional factors for consideration: [1]
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- Rash duration: Did your rash last more than a week?
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- Reaction speed: Did the reaction occur within the first hour, especially with itching on palms, soles, or scalp?
*The third criterion of PEN-FAST (treatment required for reaction) is no longer used in the PEN-FAST + model.
By including these factors, PEN-FAST + improves the accuracy of identifying people who can safely take penicillin despite a history of delayed reactions.
Important Considerations
PEN-FAST and PEN-FAST + are tools to aid doctor decisions, not guarantees. Always discuss your medical history with your doctor. If you are truly allergic to penicillin, there are other effective antibiotics available.
Our Perspectives
Strengths and Limitations of PEN-FAST and PEN-FAST +
Strengths:
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- Risk stratification: These tools help identify patients with a low risk of true penicillin allergy, allowing doctors to consider penicillin, often the most effective and affordable treatment.
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- Accessibility: Simple and easy to use, making them suitable for general physicians and pharmacists.
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- Safety: With a low PEN-FAST score, the risk of a true allergic reaction to a penicillin challenge is very low.
Limitations:
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- General population focus: Designed for general patient populations, their accuracy in high-risk groups needs further study. Ideally, such patients would be referred to allergy specialists.
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- Focus on specific reactions: They focus on common reactions like hives and rashes (maculopapular exanthema). They also exclude severe reactions like anaphylaxis or severe cutaneous adverse reactions. However, they don’t account for less common but potentially dangerous reactions like drug-induced cytopenia (low blood cell count) or serum sickness.
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- Potential for missed diagnoses: Some types of penicillin allergies might be missed by the current scoring systems. Future versions might need to incorporate additional factors.
The Takeaway
PEN-FAST and PEN-FAST + are helping doctors make better decisions about penicillin allergies, leading to more people receiving the most effective treatment. If you’ve been told you have a penicillin allergy, talk to your doctor to see if these new tools can help determine if penicillin might actually be safe for you.
Conclusion
PEN-FAST and PEN-FAST + are valuable tools for initial risk assessment of penicillin allergies, enabling doctors to make informed decisions about using penicillin in low-risk patients. However, their limitations in high-risk groups and for atypical reactions necessitate using them alongside clinical judgment. By acknowledging both the benefits and limitations of these tools, we can ensure they are used effectively to improve patient care.
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