Drug allergy - Twitter summary from #ACAAI16 meeting

This is a Twitter summary from #ACAAI16 meeting. The post is a part of series. See the rest here: http://allergynotes.blogspot.com/search/label/#ACAAI16

Several allergists did a great job posting updates on Twitter from the 2016 meeting of ACAAI, the hashtag was #ACAAI16. I used the website Symplur to review the tweets:

@dranneellis @drsilge @choirdoc

http://www.symplur.com/healthcare-hashtags/acaai16/

Presentation handouts are available from the ACAAI website: http://annualmeeting.acaai.org/session_presentations.cfm

"Practical Advice for the diagnosis/management of Drug Allergy".

First speaker is Dr. Aleena Banerji "Drug Intolerance or Drug Allergy: critical role of the Allergist".

Up to half of antibiotic use is unnecessary and inappropriate. Using the correct antibiotic, when indicated, is even more critical.

Impact of self-reported penicillin allergy is huge - longer hospital stay, increased C diff, MRSA and VRE due to broad spectrum use. Longer hospital stays and increased rate of C diff, VRE for those with history of penicillin allergy.

Adverse drug reactions - all unintended pharmacology effects of a drug, except therapeutic failures, overdose, or abuse. Hypersensitivity is only a subset of drug adverse reactions - immune response leading to adverse health effects. Drug intolerances do not involve an immune response - patient can continue to use the drug and 'put up' with side effects if needed.

Dr Banerji charges us to eliminate "penicillin allergy disease" - the fear of prescribing PCN to a patient with self-reported PCN allergy.

PCN skin testing is highly effective - negative predictive value is high and subsequent use of broad spectrum ABX is reduced.

Preventing drug allergy starts with our primary care colleagues. Use antibiotics only when needed brings less chance for misunderstood reactions. Many patients with a history of rash with PCN/Amoxicillin actually have a viral infection and the antibiotic wasn't needed in 1st place.

Graded challenge is the Gold Standard for evaluating drug allergy; it is performed when low likelihood of hypersensitivity exists. In low risk patients, reaction rate is the same between 1-2 step graded challenges to antibiotics vs 3-4 step. Reaction rate to a 1-2 step challenge was identical to a 3-4 step protocol; assuming a low risk patient, both are safe.

Dr Banerji calls penicillin the wonder drug. It's what gets prescribed when you wonder what's going on.

Blumenthal’s Ann Allergy Asthma Immunology 2015 - guideline based approach to PCN allergy led to decrease of broad spectrum ABx use. Establishing antibiotic guidelines for hospitals increased use of test doses, decreased use of broad spectrum antibiotics.

Allergists can play a significant role in “de-labeling” drug allergy. If you're an allergist using EHR, it's on us to remove allergies from med allergy list. No one else is going to do it.

Dr. Eric Macy presented on "Cost Effectiveness in approaching Drug Allergy" @EricMacyMD

PCN allergy skin testing is well established as an important part of an effective antibiotic stewardship program. Currently available in vitro PCN IgE test is not useful because results don't correlate to oral challenge reactions; high false positive rate.

Study of 'PCN allergic' inpatients had a 0.59 more hospital days compared to age/gender matched controls. Study from the Netherlands showed higher hospital readmission rate in those with unconfirmed penicillin allergy on chart.

Toronto study: 23% inpatients had a self-reported "allergy" but beta-lactam was prefered ABx in 76%, 35% did not get a beta-lactam. Patients who were given a beta-lactam did not have harms unlike those who were given vancomycin or a fluoroquinolone.

Testing 308 patients for penicillin allergy saved Kaiser Healthcare over a million dollars over 6 years.

Dr. Roland Solensky presented on "Cephalosporins are not Penicillins".

Dr Solensky showed a case report of 2 patients with PCN allergy having fatal reactions to cephalosporin published in JAMA 1964/74.

Yes, penicillin and cephalosporins both have a beta-lactam ring, but side chains are different.

Initial studies evaluating PCN/Cephalosporin cross-reactivity looked at IgG/IgM (it took place in 1968 before IgE discovered!). Dr Solensky reviewed 40-50 year old data that created concern regarding cross-reactivity between PCN and cephalosporins. More recent studies (2000s) reveal a dramatically lower risk of PCN/cephalosporin cross-reactivity.

Dr Solensky's study of 606 patients with self-reported PCN allergy who were given cephalosporins anyway had only 1 patient with eczema reaction. History of PCN allergy wasn't a predictor of cephalosporin-induced anaphylaxis. EMR based study; anaphylaxis reports hand-reviewed.

Important to remember that studies of giving cephalosporins are to unproven PCN allergy - 90% will not actually be PCN allergic. However, a summary slide of all cephalosporin challenges in patients with PCN positive SPT showed 2% overall rate of reactions. About 2% of patients with PCN allergy will react to cephalosporins.

Data mining/chart review showed that new cephalosporin allergy on chart was higher in those with PCN allergy. But anaphylaxis was no higher.

Once a patient has an allergic like event (ALE) to penicillin, this increases risk of ALEs to all antibiotics. Patients with allergy like event (ALE) to PCN were as likely to have a reaction to cephalosporin as they were to structurally unrelated sulfonamide.

It is important to watch for cephalosporins with identical side chains - cefadroxil and cefprozil have the same R1 side chain as Amoxicillin. When confirmed allergy to ampicillin or amoxicillin (but negative to PCN), patients will react - 25% rate of reactions to a cephalosporin with an identical side chain.

Selective allergy to amoxicillin (not all penicillins) is very low in US - 0.35% to 1% - prevalence is higher in Europe for whatever reason. Rate seems higher in European studies (up to 45%) for unclear reasons.

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