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AND THE ANSWERS ARE . . .

  1. The large majority of patients giving histories of being allergic to penicillin antibiotics do not have allergic reactions when challenged with a penicillin agent.
    True
  2. A negative response in a penicilloyl poly lysine (PPL, Pre-Pen) skin test does not rule out the presence of current penicillin allergy.
    True
  3. The RAST detecting IgE anti-penicilloyl antibodies is more sensitive than the PPL skin test in detecting current penicillin allergy.
    False
  4. Allergic reactions to amoxicillin do not involve the beta-lactam ring structure.
    False
  5. Some allergic reactions to cephalosporins are directed against drug-specific side chains.
    True

Discussion
About 85% of patients who give a history of being penicillin allergic will tolerate oral administration of this antibiotic group. In some cases, the original diagnosis of penicillin allergy was incorrect, sometimes because a rash which appeared 1-2 days after onset of a febrile viral infection was attributed to a penicillin antibiotic taken for a presumed bacterial infection. In other cases, the patient may have had a bona fide allergic reaction to penicillin in the distant past but subsequently lost that sensitivity with time. Allergy to the penicilloyl determinant (major penicillin allergen) detected by the PPL skin test is likely present in about 80-90% of all patients currently allergic to penicillin, but not all. The commercially available anti-penicylloyl IgE RAST is about 70% as sensitive as the PPL skin test in detecting such sensitivity. If a negative PPL skin test is accompanied by a negative response to a valid minor determinant mix (MDM) skin test material (when available) this combination will have close to 100% negative predictive value for an allergic reaction to a therapeutic dose of a penicillin group antibiotic. Allergic reactions to amoxicillin generally involve the beta lactam ring shared by all members of the penicillin group. There are also atypical adverse reactions to amoxicillin with less defined mechanisms. Allergic reactions to cephalosporins may occur because of sensitization to cephalosporin determinants shared with penicillin or to side-chain haptens unique to particular cephalosporin drugs.

References

1. Mayo Clin Proc. 2005 ;80:405-10.
2. Immunol Allergy Clin North Am. 2004 ;24:463-76
3. Ann Allergy Asthma Immunol. 2002 ;88:1-3

 



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