From the Guidelines
For a patient with a penicillin allergy, it is crucial to assess the true nature of the allergy and consider the risk of cross-reactivity before selecting an alternative treatment, as less than 10% of patients with a reported penicillin allergy are truly allergic 1. When treating a patient with a penicillin allergy, the following steps should be taken:
- Assess the patient's allergy history to determine the severity and type of reaction
- Evaluate the pros and cons of alternative antimicrobial treatments
- Consider the risk of cross-reactivity with other antibiotics
- Choose an alternative treatment that is safe and effective for the patient's condition Some alternative treatments for common infections in patients with penicillin allergy include:
- Doxycycline or respiratory fluoroquinolones (such as levofloxacin or moxifloxacin) for acute bacterial rhinosinusitis 1
- Ciprofloxacin plus clindamycin or aztreonam plus vancomycin for neutropenic patients with cancer 1 However, for a patient with a penicillin allergy who needs treatment for onychomycosis (nail fungus), I recommend using oral terbinafine 250 mg daily for 6 weeks for fingernails or 12 weeks for toenails, as it is a non-penicillin alternative that is effective against dermatophytes that commonly cause nail infections. It is essential to confirm the diagnosis with a KOH preparation or fungal culture and consider checking liver function tests before initiating oral therapy, as these medications can cause hepatotoxicity 1. Treatment success should be monitored by clinical improvement and possibly follow-up cultures if needed. The most recent and highest quality study 1 supports a more liberal approach towards patients with a suspected antibiotic allergy, emphasizing the importance of assessing the risk of recurrence of an allergic reaction and choosing alternative treatments that are safe and effective.
From the FDA Drug Label
Syphilis–early: Patients who are allergic to penicillin should be treated with doxycycline 100 mg, by mouth, twice a day for 2 weeks Syphilis of more than one year’s duration: Patients who are allergic to penicillin should be treated with doxycycline 100 mg, by mouth, twice a day for 4 weeks. The patient with a penicillin allergy can be treated with doxycycline. The dosage will depend on the specific condition being treated, but for syphilis, the recommended dose is 100 mg, by mouth, twice a day for a duration of 2 weeks for early syphilis or 4 weeks for syphilis of more than one year’s duration 2.
From the Research
Treatment Options for Penicillin-Allergic Patients
- For patients with a penicillin allergy, the use of third- or fourth-generation cephalosporins or cephalosporins with dissimilar side chains than the offending penicillin carries a negligible risk of cross allergy 3.
- Cephalosporins can be prescribed safely for penicillin-allergic patients, with some exceptions such as cefadroxil, which has a higher risk of cross reactivity 4.
- The overall cross-reactivity rate between penicillins and cephalosporins is approximately 1% when using first-generation cephalosporins or cephalosporins with similar R1 side chains 3.
- Cross-reactivity between penicillin and cephalosporin drugs occurs in about 2% of cases, less than the 8% reported previously 5.
Evaluation of Penicillin Allergy
- Evaluation of penicillin allergy before deciding not to use penicillin or other β-lactam antibiotics is an important tool for antimicrobial stewardship 5.
- Penicillin skin testing carries a negative predictive value that exceeds 95% and approaches 100% when combined with amoxicillin challenge 5.
- Direct amoxicillin challenge is appropriate for patients with low-risk allergy histories, while moderate-risk patients can be evaluated with penicillin skin testing 5.
Management of Penicillin Allergy
- Treatments for penicillin allergy include penicillin discontinuation, and depending on the type of reaction, epinephrine, antihistamines, and/or glucocorticoids 6.
- Desensitization may be used in some cases where treatment with penicillins is essential 6.
- Most beta-lactams may be safely used in penicillin-allergic patients, with the possible exception of first-generation and second-generation cephalosporins 6.