Allergic Reactions to Penicillin

Introduction to Allergic Reactions

• Allergic reactions to penicillin can occur at any point during treatment, including after multiple doses have been tolerated, and can be categorized based on timing, including immediate, accelerated, and delayed reactions, with facial swelling being a concerning symptom that may indicate a potentially serious IgE-mediated allergic reaction, as noted by the Dutch Working Party on Antibiotic Policy guideline 1

Diagnosis and Management

• The American Academy of Allergy, Asthma, and Immunology recommends referral to an allergist for formal evaluation after an acute phase has resolved, which may include skin testing with major and minor determinants of penicillin, and approximately 10% of patients who report penicillin allergy are truly allergic when tested, according to the Centers for Disease Control and Prevention 2, 3
• Immediate actions for suspected allergic reactions include discontinuing penicillin, assessing airway, breathing, and circulation, administering epinephrine if signs of anaphylaxis are present, and considering antihistamines and corticosteroids for symptom management, as recommended by the Clinical Microbiology and Infection guideline 1
• The skin test for penicillin is the standard method for diagnosing IgE-mediated penicillin allergies, with a negative predictive value of 97-99% and a positive predictive value of at least 50% 4

Classification of Allergic Reactions

• Allergic reactions to penicillin can be differentiated mainly by their immunological mechanism, with IgE-mediated reactions being immediate and potentially severe, and non-IgE-mediated reactions being typically delayed and presenting with different clinical manifestations 4
• IgE-mediated reactions are characterized by immediate or accelerated onset (less than 1 hour to 72 hours after exposure) and clinical manifestations include urticaria and angioedema (85-90% of cases), cutaneous flushing (45-55%), anaphylaxis, hypotension, dizziness or syncope (30-35%), and respiratory symptoms such as dyspnea, wheezing, or upper airway angioedema (40-60%) 4, 5
• Non-IgE-mediated reactions are characterized by a delayed onset (more than 72 hours after exposure) and clinical manifestations include maculopapular eruptions, erythema multiforme, serum sickness, hemolytic anemia, and severe cutaneous reactions such as Stevens-Johnson syndrome or toxic epidermal necrolysis 4, 5

Management of Penicillin Allergy

• Patients with a positive penicillin skin test should not receive penicillin conventionally, and management options include administration of a non-beta-lactam antibiotic, penicillin desensitization if absolutely necessary, or consideration of certain beta-lactams with low cross-reactivity risk 4, 3, 6
• Monobactams (aztreonam) can be used safely in patients with penicillin allergy, except in cases of ceftazidime allergy, and carbapenems should be considered to have cross-reactivity with penicillin 4
• The cross-reactivity between penicillin and cephalosporins is lower than previously thought, occurring in approximately 2% of cases 4
• Patients with a history of severe non-IgE-mediated reactions to penicillin (such as Stevens-Johnson syndrome or toxic epidermal necrolysis) should not undergo skin testing, and patients at high risk of anaphylaxis should be evaluated with 100-fold lower dilutions of skin test reagents before using full-concentration reagents 4, 3, 6, 2

Future Considerations and Alternative Treatments

• The Dutch Working Party on Antibiotic Policy guideline recommends avoiding penicillin class antibiotics until formal allergy evaluation, and considering alternative antibiotics if needed for current infection 1
• Cross-reactivity with other beta-lactam antibiotics, such as cephalosporins and carbapenems, should be considered in future antibiotic selection, according to the MMWR Recommendations and Reports 2
• For patients with colitis who have a penicillin allergy, metronidazole is the first-line treatment option, with vancomycin reserved for those who cannot tolerate or have not responded to metronidazole, as recommended by the Infectious Diseases Society of America 7
• The Infectious Diseases Society of America recommends using metronidazole or vancomycin for C. difficile colitis, and considering fluoroquinolones plus clindamycin for other bacterial infections associated with colitis 7
• Patients labeled as having penicillin allergy are exposed to more alternative antibiotics and have increased prevalence of C. difficile, MRSA, and VRE infections, highlighting the importance of penicillin allergy testing 8
• The American Academy of Allergy, Asthma, and Immunology suggests considering penicillin allergy testing when appropriate to potentially remove incorrect penicillin allergy labels, as many patients labeled as penicillin-allergic are not truly allergic 8, 5, 4, 3, 2
• Recurrence of C. difficile infection occurs in approximately 20% of cases, and monitoring for therapeutic response and watching for recurrence of symptoms after antibiotic completion is crucial 7