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  • penicillins belong to the group of antibiotics (including cephalosporins) which act upon the beta lactam ring and thus compromise the bacterial cell wall in a bactericidal manner
  • penicillins act via binding to penicillin-binding proteins on the bacterial cell wall

hypersensitivity to penicillins

  • reactions to beta-lactam antibiotics can be classified into:
    • immediate
      • IgE mediated and classically manifest as anaphylaxis, urticaria, angioedema, bronchospasm and allergic rhinoconjunctivitis.
      • occurs in ~10% of patients with “allergy” to penicillin
      • while penicillin-induced anaphylaxis is rare (0.01-0.05% of courses), it may be fatal in 10% of cases
      • it is difficult to obtain reliable data about the frequency of cephalosporin anaphylaxis, but published figures are 0.0001-0.1%
    • non-immediate
      • such as maculopapular or morbilliform rashes are probably T-cell mediated.
      • less common but serious adverse reactions to cephalosporins include serum sickness-like reactions, acute interstitial nephritis and cytopenias.

cross-sensitivity - can a penicillin allergic patient be given cephalosporins safely?

  • penicillins and cephalosporins exhibit partial and incomplete cross-reactivity
    • early studies in the 1960's and 1970's suggested that this was ~18% (ie 18% of patients with penicillin allergy would also have cephalosporin allergy), however, these studies were apparantly falsely high due in part to being done at a time when cephalospirins were often contaminated with penicillin
      • before the 1980s, pharmaceutical companies used Acremonium (formally called Cephalosporium) to create both penicillins and cephalosporins
      • in addition, the authors of the early studies loosely defined ‘‘allergy’’ and did not account for the fact that penicillin-allergic patients have an increased risk of adverse reactions to any medication
    • patients with a penicillin allergy have a ~3x normal risk of other allergies - even to medications not structurally related to penicillins
    • the overall cross reactivity between penicillins and cephalosporins in individuals who report a penicillin allergy is approximately 1% and, in those with a confirmed penicillin allergy, 2.55%. 1)
    • cross-reactivity between penicillins and 3rd generation cephalosporins approaches 0% 2)
  • Camapagna et al recommend that in patients with a documented IgE-mediated response to penicillin, third- and fourth-generation cephalosporins can be used generously. First- and second-generation cephalosporins with R1 side chains similar to that of penicillin (ie, cefaclor, cefadroxil, cefatrizine, cefprozil, cephalexin, and cephradine) should be avoided 3)
  • a history of mild reactions to penicillin, such as rashes, does not imply that a reaction to cephalosporins will not be life-threatening - if a 1st or 2nd generation cephalosporin is prescribed to a patient with penicillin allergy, the first dose should be taken in a monitored setting 4)

classes of penicillins

narrow spectrum:

  • mainly active against Gram +ves, Neisseria & enterococci

beta lactamase resistant:

broad spectrum aminopenicillins:

  • active against many Gram -ves but NOT Enterobacter, indole+ve Proteus
  • eg. amoxycillin/amoxicillin, ampicillin


  • active against Pseudomonas but used with aminoglycosides to prevent resistance developing.
  • eg. carbenicillin, ticarcillin, piperacillin

beta lactamase inhibitors:

  • substances that resemble beta lactams & competitively inhibit beta lactamases
  • used to extend the activity of penicillins
  • eg. clavulanic acid, sulbactam, tazobactam (see Tazocin (piperacillin + tazobactam))
1) , 3)
J.D.Campagna et al. The Journal of Emergency Medicine, Vol. 42, No. 5, pp. 612–620, 2012
Anne S, Reisman RE. Risk of administering cephalosporin antibiotics to patients with histories of penicillin allergy. Ann Allergy Asthma Immunol 1995;74:167-170.
penicillins.txt · Last modified: 2017/04/02 23:07 by

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