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Tag: penicillin

Dear Dr K:

Dear Dr K:

You tested me to see if my childhood recollection of penicillin allergy was still valid.  Even though the tests showed I was not allergic my PCP still won’t prescribe it when I need an antibiotic.  Why the reluctance?

The simple and short answers are; medical malpractice and labeling.  Roughly 10% of malpractice suits are concerning medication errors.  Physicians are aware of this.  For some reason, once a person is labeled as “penicillin allergic” there is great reluctance to remove this label.  As it turns out, 12% of the American population carries this label.  However, when academic centers have done studies to confirm this diagnosis only 5% of this group is actually proven to be allergic.  So, to look at that in terms of numbers; for every 1,000 Americans 120 carry the penicillin label and only 6 are actually allergic.

The problem is that of these 6 individuals the potential exists for a life-threatening anaphylactic reaction.  So, many people (including doctors) choose what at first blush seems to be the safer route: avoid penicillin.  Unfortunately, this in not always a safer choice.  By denying the patient the “first line” treatment choice it results in utilizing less desirable and problematic antibiotics such as fluoroquinolones, vancomycin and clindamycin.  These antibiotics have their own potential to cause medical mischief such as tendon rupture, Clostridium difficile (C. diff) colitis, and the development of super resistant bacteria such as MRSA and VRE (vancomycin – resistant – enterococcus).  The University of Oregon has done research into this problem.  They posit that roughly 30 million Americans are mislabeled as penicillin allergic.  They found that patients so labeled have increased medical costs and longer hospital stays compared with patients not felt to be penicillin allergic.  The other dynamic that the University of Oregon researchers studied was the question of cross reactivity between penicillin and a separate family of antibiotics called cephalosporins.

Again, they discovered that most doctors will not prescribe cephalosporins to patients with penicillin allergy because of a fear of cross reactivity.  In fact, drug manufacturers include in their package insert the possibility for this interaction even though there is little or no evidence from scientific studies of a cross reactivity.  Most recent research would indicate that the small number of individuals who are allergic to both penicillin and cephalosporin have this dual allergy not because of a direct cross reactivity but because being an allergic individual per se raises their risk for developing separate but individual drug allergies.

Dear Doc: Penicillin/Cephalosporin — cross-reactive?

Dear Doc: Penicillin/Cephalosporin — cross-reactive?

Dear Dr. K: I’m allergic to penicillin but my pharmacist has also labeled me cephalosporin-allergic. I’ve never taken cephalosporin. Should I follow her advice?

I can’t give you an answer with a 100 percent surety, but I can come close. As luck would have it, Kaiser Permanent Health Care just finished a research project on cephalosporin allergy.

Their study included 820,000 patients who received a total of 1.4-million courses of cephalosporin (often prescribed as Keflex). Of these, 66,000 were allergic to penicillin. Only one-half a percent of the 820,000 had an allergy to cephalosporin.

The reason your pharmacy warns of a possible cross-reactivity is that penicillins and cephalosporins share a common structural feature called the Beta-lactam ring. The thing that distinguishes penicillins from cephalosporins are side-chain molecules that attach to the Beta-lactam ring. Luckily, most allergy to penicillin is directed against the side chain and not the ring structure. Hence, there would not be cross-reactivity.

The Kaiser Permanent researchers felt that since the potential for cross-reactivity is so low, penicillin-allergic individuals can go ahead and take cephalosporins in most cases. They did advise members of this group who have had anaphylaxis to consider antibiotic testing prior to receiving cephalosporins. (Also, see first item in Q-Tips this issue.)