Table of Contents
- 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:
- 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%
- 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
- mainly active against Gram +ves, Neisseria & enterococci
- eg. benzyl penicillin, Pen V, procaine penicillin
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
- see also Tazocin (piperacillin + tazobactam)
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))
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 127.0.0.1