Chapter 4: Allergies

ALLERGIES: _______________________________________________

I.   Significance

A.     A history of an allergy to a vital drug could be a death

            sentence.

B.    The major allergies encountered in burn care are to b-lactam antibiotics and sulfa drugs.

II. History

A.    Patients stating any allergic history must be taken

seriously and penicillin should be held pending further investigations.

B.    An accurate history of the specific reaction elicited is

important.

C.    You need to distinguish between:

1.   A true allergic reaction which is anaphylaxis (i.e. hypotension, laryngeal edema, bronchospasm) and cutaneous reactions

             2.   Nonspecific symptoms (i.e. headache, nausea, emesis).

III.  Penicillin allergy

A.      Penicillin allergy is the most prevalent immunological drug reaction in clinical medicine. IgE antibodies directed against the b-lactam ring are responsible for the type 1 reaction seen.  If a patient gives a history of an urticarial rash and bronchospasm the diagnosis of penicillin allergy is made. Though penicillin allergies are often diagnosed in childhood, studies of this age group show that over-diagnosis of penicillin allergy may occur in up to 94% of cases.[i]  Penicillin is regarded as the most important antimicrobial agent in greatly reducing hemolytic streptococcal and clostridial infections, and is often used to treat burn cellulitis.

B.          Can we use cephalosporins?

1.          The overall incidence of adverse reactions from cephalosporins ranges from 1% to 10%, with rare anaphylaxis (< 0.02%). Post-marketing studies of second and third generation cephalosporins showed no increase in allergic reactions in patients with a history of penicillin allergy.  Similarly, patients with cephalosporin allergies have a very small risk of penicillin reactions.

2.          A patient who states he or she has a history of rash to penicillin can be treated instead with a first generation cephalosporin.  Patients with anaphylactic reactions to penicillin should receive neither penicillin nor cephalosporin.  These patients can be treated with vancomycin and penicillin desensitization in conjunction with recommendations by an infectious disease specialist. Intravenous desensitization is a rapid, safe, and effective technique for patients demonstrating hypersensitivity to beta-lactam antibiotics who require therapy with these medications.[ii]^,[iii]

3.          Penicillin skin tests are not used, as they do not predict the likelihood of allergic reactions to cephalosporins in patients with histories of penicillin allergy. [iv]

4.          RAST is a solid-phase sandwich radioimmunoassay to detect allergen-specific IgE antibodies.  The AlaSTAT test is an enzymoimmunoassay alternative to the RAST that is more rapid.  Neither of these is commonly used in confirming drug allergies.

C.                Sulfa allergies

Allergies to silver sulfadiazine and mafenide acetate, the two topical agents used most widely in burn therapy today, have been reported.[v]^{,[vi],[vii],[viii],[ix]}  The reactions are usually mild.  Serious hypersensitivity to these agents has been rarely described.[x]^,[xi]   Only 2 to 5 percent of patients treated with silvadine cream exhibit a minor maculopapular rash that rarely requires discontinuation of the agent, and 5 to 50 percent of patients treated with mafenide acetate develop a rash that is easily controlled with antihistamines and also does not require discontinuation.^9,10,11