Drug Allergies Flashcards
Are most drug allergies true?
Although reported drug allergies are common, true drug allergies are less common
What happens when people are mislabelled as allergic to a specific antibiotic?
Labelling someone with a drug allergy can be dangerous if
they subsequently require that drug in the future and are
denied access to it
Antibiotic allergies are usually from the past so when the
patient presents with a new antibiotic Rx they will not
generally have signs or symptoms
How likely are beta-lactam allergies?
In a given group of 10,000 patients:
1000 will report to have a pen “allergy”
Less than 100 have a true IgE-mediated allergy
1 will have a anaphylactic reaction to penicillins
How to tell if a true penicillin allergy applies to all beta-lactams?
If the allergy is to the beta-lactam ring, the patient will be allergic to all beta-lactams
Allergy may also occur to the side chain (R1) in which case
allergy will be to the specific drugs that share that side chain
What is cross-sensitivity?
This is the presence of allergic reactions to multiple classes of antibiotics
ex. Cephalosporin and penicillin allergies in a patient occur in 1-3% of cases
What are the three types of drug reactions caused by beta-lactams?
Penicillin adverse effects
Severe penicillin adverse effects
True IgE mediated allergy
What are some lower level reactions to penicillin/beta-lactams?
Diffuse non-itchy rash (10%), GI upset, headache
These symptoms appear after 2-5 days of therapy and may last several days to weeks
Not IgE mediated
It is safe to prescribe penicillins and cephalosporins to people who have had these reactions
What are some severe penicillin adverse effects?
Stevens-Johnson syndrome, toxic epidermal necrolysis (TENS),
interstitial nephritis, hemolytic anemia, serum sickness
Not IgE-mediated
All beta- lactams are contraindicated
What do true IgE mediated allergies look like?
Itchy rash or hives
Angiodema, hypotension, bronchospasm
Reactions usually develop with an hour after dose
Can be life-threatening
Anaphylaxis
How are false drug allergies delabelled?
Skin tests:
If the results are negative, previously unavailable drugs are now safe for use
If the results are positive or cannot test, avoid drug/drug class in question. Use alternatives
What is desensitization in terms of drug allergies?
In individuals who have reactions to a particular drug, very small doses can be stared and ramped up gradually. This needs to be done each time the drug in question has to be used
What types of drugs contain sulfonamides?
Antibiotics, thiazide and loop diuretics, oral hypoglycemic, COX-2 inhibitors and carbonic anhydrase inhibitors
Also antivirals
What percentage if people have reactions to sulfa drugs?
Rates of allergic reactions 4.8% (antibiotic sulfonamides) and 2%
(nonantibiotic sulfonamides)
Are cross-sensitive reactions between antibiotic sulfas and non-antibiotic sulfa drugs
Highly unlikely that there will be cross-reactivity between
sulfonamide antibiotics and non-
antibiotics
Are penicillin reactions worse compared to sulfa reactions?
No, A reaction from a sulfa drug is more likely to be serious than penicillin. SJS and TEMS is more common
If fever of swollen lymph nodes are experienced in a reaction with sulfa, avoid sulfa drugs
