Penicillin Allergy Cross Reactivity


  1. Only 0.5% to 2% of patients with a documented penicillin allergy that are administered a penicillin will exhibit a hypersensitivity reaction, usually presenting as a rash or hives.
  2. True IgE-mediated penicillin allergies that cause anaphylaxis are rare.
  3. An IgE-mediated penicillin allergy can diminish over time, as 80% of patients become tolerant after a decade.
  4. Patients with a documented penicillin allergy may be inappropriately exposed to alternative antibiotics, resulting in increased treatment failures, adverse effects, and antimicrobial resistance.
  5. Penicillins, cephalosporins, and carbapenems all share a beta-lactam core structure, thus raising the potential for cross-reactivity among these agents.


  • The following drugs in each group may have cross-reactivity to each other due to similar side chains
  • Cross-reactivity between penicillins and cephalosporins is about 2%
  • Cefazolin is NOT likely to cross react with penicillin (side chains NOT similar)
  • Cross-reactivity with monobactams (i.e. aztreonam) is negligible
  • Cross-reactivity between penicillins and carbapenems is <1%
Group 1Group 2Group 3Group 4
Cefpodoxime Ceftaroline
Ceftolazane Ceftazidime

Overview of Evidence

AuthorDesignIntervention & ComparisonOutcome
Why Cross-Reactivity?
Nagakura, 1990   Mayorga, 1995    Animal study-Studied antibodies formed when animals were immunized with protein-beta-lactam conjugates-92% of the antibodies recognized an epitope in which the side chain was the main constituent -The side chain is the most important determinant in penicillin immunogenicity
Goodman, 2001Retrospective review (n=2933)-Orthopedic patients with penicillin allergy receiving cefazolin prior to a procedureOnly 1 patient may have had an allergic reaction to cefazolinCross-reactivity rate with cefazolin was 0.33%
  Daulat, 2004  Retrospective review (n=606)-Patients with penicillin allergy receiving cephalosporins -42% 1st gen., 21% 2nd gen., and 37% 3rd or 4th gen. cephalosporinsOnly 1 patient had an allergic reaction that was documented as worsening of underlying eczema after being placed on cefazolinCross-reactivity was 0.17%
    Apter, 2006    Retrospective review (n=3920)-Patients with a prescription for penicillin followed by a prescription for a cephalosporin -Identified allergic-like events within 30 days after each prescriptionOnly 43 patients who experienced an allergic- like reaction after both penicillin and cephalosporinCross-reactivity rate was 1.1%70% of these patients just had urticariaThe risk of anaphylaxis to cephalosporins was only 0.001%
Romano, 2018Prospective review (n=252)Prospective study of 252 subjects with IgE-mediated hypersensitivity to penicillins – Serum specific IgE assays for cefaclor and skin tests for 10 cephalosporins   -Oral challenges with cefuroxime axetil, ceftriaxone, cefaclor, and cefadroxil for subjects with negative skin tests99 subjects (39.3%) had positive allergy tests for cephalosporins 95 subjects (37.7%) were positive to aminocephalosporins and/or cefamandole, which share side chains with penicillins All 244 subjects who underwent challenges with cefuroxime axetil and ceftriaxone tolerated them 7 subjects reacted to cefaclor or cefadroxil
    Romano, 2006  Prospective study (n=112)-Skin tested to penicillins and then skin tested to imipenem -If skin test to imipenem was negative, then challenged with IM doseOnly 1 patient of the penicillin skin-test positive patients had a positive skin test to imipenemCross-reactivity rate was 0.9%None of the 110 patients with a negative imipenem skin test that underwent IM challenge had a reaction
  Romano, 2007  Prospective study (n=104)        -Skin tested to penicillins and then skin tested to meropenem -If skin test to imipenem was negative, then challenged with IV doseOnly 1 patient of the penicillin skin-test positive patients had a positive skin test to meropenemCross-reactivity rate was 1%All 103 patients with a negative meropenem skin test tolerated the IV challenge
  Atanaskovic- Markovic, 2008  Prospective study (n=108)-Children with penicillin allergy were skin tested to penicillin and meropenem -If skin test to meropenem was negative, then challenged with IV doseOnly 1 patient with a positive penicillin test reacted to the meropenem skin testCross-reactivity rate was 0.9%All 107 patients with a negative meropenem skin test tolerated the IV challenge
Sánchez de Vicente, 2020Prospective study (n=137)  Tolerance testing for cephalosporins and carbapenems in patients with confirmed penicillin allergy0/46 patients showed positive skin tests for imipenem. 0.79% (1/137) patients showed a positive skin test for cefuroxime.0.79% (1/137) patients showed a positive skin test for  ceftriaxone.


  1. True penicillin allergies are less common than reported, and anaphylaxis is uncommon.
  2. Cross-reactivity among penicillins and cephalosporins is attributed to similarity in side chains.
  3. Cephalosporin cross-reactivity with penicillins is much lower than reported in early studies partly due to contamination of study drugs with penicillin.
  4. Cross-reactivity between cephalosporins is about 2% and with carbapenems is <1%


  1. Apter AJ, Kinman JL, Bilker WB, et al. Is There Cross-Reactivity Between Penicillins and Cephalosporins? Am J Med. 2006;119(4):354e11-19.
  2. Atanaskovic-Markovic M, Gaeta F, Medjo B, Viola M, Nestorovic B, Romano A. Tolerability of Meropenem in Children with IgE-Mediated Hypersensitivity to Penicillins. Allergy. 2008;63:237-240.
  3. Blumenthal KG, Shenoy ES, Wolfson AR, et al. Addressing Inpatient Beta-Lactam Allergies: A Multihospital Implementation. J Allergy Clin Immunol Pract. 2017;5(3):616-625.
  4. Blumenthal KG, Huebner EM, Fu X, et al. Risk-Based Pathway for Outpatient Penicillin Allergy Evaluations. J Allergy Clin Immunol Pract. 2019;7(7):2411-2414.
  5. Campagna JD, Bond MC, Schabelman E, Hayes BD. The Use of Cephalosporins in Penicillin-Allergic Patients: A Literature Review. J Emerg Med. 2012;42(5):612-620.
  6. Chaudry SB, Veve MP, Wagner JL. Cephalosporins: A Focus on Side Chains and Beta-Lactam Cross-Reactivity. Pharmacy. 2019;7:1-16.
  7. Daulat S, Solensky R, Earl HS, Casey W, Gruchalla RS. Safety of Cephalosporin Administration to Patients with Hstories of Penicillin Allergy. J Allergy Clin Immunol Pract. 2004;113(6):1220-1222.
  8. DePestel DD, Benninger MS, Danziger L, et al. Cephalosporin Use in Treatment of Patients with Penicillin Allergies. J Am Pharm Assoc. 2008;48:530-540.
  9. Goodman EJ, Morgan MJ, Johnson PA, Nichols BA, Denk N, Gold BB. Cephalosporins can be Given to Penicillin-Allergic Patients Who Do Not Exhibit an Anaphylactic Response. J Clin Anesth. 2001;13(8):561-564.
  10. Mayorga C, Obispo T, Jimeno L, et al. Epitope Mapping of Beta-Lactam Antibiotics with the Use of Monoclonal Antibodies. Toxicology. 1995;97:225-234.
  11. Nagakura N, Souma S, Shimizu T, Yanagihara Y. Anti-Ampicillin Monoclonal Antibodies and their Cross- Reactivities to Various Beta-Lactams. Br J Hosp Med. 1990;44:252-258.
  12. Romano A, Viola M, Gueant-Rodriguez RM, Gaeta F, Pettinato R, Gueant JL. Imipenem in Patients with Immediate Hypersensitivity to Penicillins. N Engl J Med. 2006;354:2835-2837.
  13. Romano A, Viola M, Gueant-Rodriguez RM, Gaeta F, Valluzzi R, Gueant JL. Brief Communication: Tolerability of Meropenem in Patients with IgE-Mediated Hypersensitivity to Penicillins. Ann Intern Med. 2007;146:266-269.
  14. Shenoy ES, Macy E, Rowe T, Blumenthal KG. Evaluation and Management of Penicillin Allergy: A Review. JAMA. 2019;321(2):188-199.
  15. Sánchez de Vicente J, Gamboa P, García-Lirio E, Irazabal B, Jáuregui I, Martínez MD, Segurola A, Seras Y, Galán C. Tolerance to Cephalosporins and Carbapenems in Penicillin-Allergic Patients. J Investig Allergol Clin Immunol. 2020;30(1):75-76. doi: 10.18176/jiaci.0463. Epub 2019 Nov 4. PMID: 31680067.
  16. Romano A, Valluzzi RL, Caruso C, Maggioletti M, Quaratino D, Gaeta F. Cross-Reactivity and Tolerability of Cephalosporins in Patients with IgE-Mediated Hypersensitivity to Penicillins. J Allergy Clin Immunol Pract. 2018 Sep-Oct;6(5):1662-1672. doi: 10.1016/j.jaip.2018.01.020. Epub 2018 Feb 3. PMID: 29408440.

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