Thread by @LearnwithDrAksh

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How many of you do Skin test before administration of antibiotics?

Most Indian hospitals test for antibiotic sensitivity, without knowing the basis of testing
Lets learn a lil about Antibiotic allergy testing 🧵
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1. Skin test - Is done to identify hypersensitivity - which can be IgE or Non IgE mediated. Hence, sensitivity can be seen within 1h (IgE mediated) or >1h (Non-IgE mediated)
So, no guarantee that a patient with skin test negative will not have hypersensitivity later

2. Adverse reaction - Rawlins and Thompson
Type A - Dose dependent & predictable
Type B - Dose independent & unpredictable
Drug allergies are generally Type B 3

3. Skin tests are validated for beta-lactams only when penicillin allergy history is present (Not Family history)
Routine testing of Cephalosporins sensitivity is NOT RECOMMENDED (Most commonly done - before surgical prophylaxis)

4. Lets talk about how testing is done - Ideally, inject antibiotic with Positive control - usually histamine, and negative control - usually Saline - Observe for wheal
Positive skin test is >3mm wheal with flare wit no response in negative control & 5mm wheal in Positive control

5. Method of testing - One cant inject the penicillin to be given Intradermally to test for sensitivity -
Both major penicillin antigenic determinants
Penicilloyl-polylysine - PPL & minor determinants
(benzylpenicillin [penicillin G], benzylpenicilloate & benzylpenilloate)

7. Skin testing with penicillin G alone without the use of
PPL is not recommended, because up to 70% of patients who have
a positive skin test result react only to PPL, and these patients can
still have a severe reaction
In India PPL is not available

8. Testing for other antibiotics is not standardised
Vancomycin testing to predict Vancomycin induced hypersensitivity (Redman syndrome) is NOT RECOMMENDED
This reaction is infusion rate based -if patient develops wheals flushing - reducing rate of infusion will solve problem

9. Large majority are mislabelled penicillin allergic - will lead to unnecessary broad spectrum & expensive antibiotic use - contributing to AMR

10. So, When to do?
Ask any history - If no history - Don't do
Don't do universal Skin test
Even if positive - alternative Cephalosporins & Non-penicillin beta lactam can be used
There is little or no cross reactivity between

Most hypersensitivity reactions to cephalosporins are directed at the R-group
side chain rather than the core b-lactam ring molecule
Similar (gray) or an identical (red) side chain

11. Penicillin allergy doesn't mean patient will be life long allergic -85% can tolerate readministration

12.Further reading: japi.org/q2f494b4/skin-…
jaci-inpractice.org/article/S2213-…