Allergy/immunology Flashcards
What’s a possible approach for pts with mild symptoms following penicillin exposure, not suggestive of IgE-mediated reaction?
consider direct oral DPT- risk of true allergy can’t be predicted with high S&S from clinical Hx but it could be used to risk stratify pts for DPT; advantage= lack of need for skin testing reduces time & cost & DPT is non-invasive & convenient for pts. disadvantage= data is strongest in children, no clear consensus re: which pts considered “low risk” to forgo skin testing.
What to tell pts who are de-labelled from penicillin allergy following skin test, DPT or both?
advise that they have same risk as general population for developing new allergy to penicillin in the future- anyone may become sensitised to penicillin during their lifetime.
DPT for a single penicillin doesn’t preclude allergy to other penicillins as side-chain sensitivity may be missed with a single-drug DPT.
What to tell pts who are de-labelled from penicillin allergy following skin test, DPT or both?
advise that they have same risk as general population for developing new allergy to penicillin in the future- anyone may become sensitised to penicillin during their lifetime.
DPT for a single penicillin doesn’t preclude allergy to other penicillins as side-chain sensitivity may be missed with a single-drug DPT.
Problems with label of penicillin allergy?
antimicrobial resistance increased SSI risk of allergy to alternative antibiotic hospital readmission rates prolonged hospital stay cost more ED visits
Is there carbapenem cross-reactivity with penicillins or cephalosporins? monobactams & penicillins? btwn ceftazidime (3rd ten) & aztretonam? Why is the 1970s figure of 10% cross-reactivity btwn penicillin & cephalosporins incorrect?
it’s very low
apparently no cross-reactivity btwn monobactams & penicillins
yes due to R1
the early studies of penicillin & cephalosporin cross-reactivity were tainted by presence of trace amounts of benzylpenicillin in the cephalosporins, falsely elevating the apparent degree of cross-reactivity.
What’s the incidence of anaphylaxis to parenteral cephalosporins? penicillins?
- 00016%
0. 002%
What determines the variation in cross-reactivity btwn penicillin & cephalosporins? does cefazolin have similar R1 or R2 side chains to penicillins or other cephalosporins (except ceftezole)?
structural differences among cephalosporins.
All share with penicillin a 4-membered B lactate ring.
The cross-reactivity is likely related to the R1 & R2 side-chain moieties that vary between the generations of cephalosporins; side-chain similarity likely contributes to cross-reactivity however the R1 & R2 side chains are not always the antigenic determinant. Cephazolin does not have similar R1 or R2 side chains to either penicillin or other cephalosporins except for ceftezole (a 2nd gen).
No. It also offers superior GP antimicrobial activity cf cephalosporins of later generations.
What’s the risk of a reaction to a cephalosporin in those with true penicillin allergy?
2-5%
Which pts with a label of penicillin allergy could be considered for direct oral DPT if lack of time or local expertise precludes prior skin testing? (those with Asterix could be de-labeled based on Hx)
Those with minor GI symptoms*
Hx only thrush*
FHx but no personal Hx of penicillin allergy*
pt can’t recall shy they had the label but have had @ least one course of penicillin without adverse effect*
Hx of minor symptoms not suggestive of allergy (eg headache) & didn’t require Rx*
Benign rash (non-itchy, non-blistering, non-severe, >1hr after first dose) >10yrs ago, provided it didn’t require Rx
Which pts with a label of penicillin allergy could be considered for skin testing +/- DPT?
Rash but no details remembered
itchy rash
can’t recall the reaction
symptoms not in the criteria for specialist Ax, but required Rx
Which pts need specialist allergist evaluation?
-Hx immediate & severe reaction with wheeze, dyspnoea, angioedema, tachycardia, swelling, low BP, collapse, cardiac arrest, loss of consciousness; the allergist may consider them for penicillin desensitisation if there’s an absolute indication for penicillin (if they had desensitisation it would NOT result in de-labeling of the pt)
Which pts are contraindicated from receiving penicillins & should not be offered penicillin testing?
those with severe or blistering rash at any time during or in weeks after a course of penicillin Rx, or a Dx of drug reaction with eosinophilia & systemic symptoms syndrome, SJS or TEN
Which pts are contraindicated from receiving penicillins & should not be offered penicillin testing? Which other pts should not have DPT?
those with severe or blistering rash at any time during or in weeks after a course of penicillin Rx, or a Dx of drug reaction with eosinophilia & systemic symptoms syndrome, SJS or TEN
pts with severe or unstable IHD or those who are pregnant
Pts with severe aortic stenosis
Should pts with severe asthma or COPD be excluded from DPT?
no consensus- up to discretion of treating team- balance of risks of need for penicillin & likelihood of harm from a severe allergic reaction
What may occur if pts on chemotherapy undergo DPT?
they may get a false negative
