From Allergy Notes: Only 6.8% of children with “rash due to penicillin” have penicillin allergy; (oh and I mention The Syph)
Finally!: There is evidence that, in kids labelled with ‘penicillin allergy’, it is not the penicillin that causes the rash, but rather, the underlying virus (for which the penicillin was erroneously prescribed) that likely causes the rash. For more details: *See the post at Allergy Notes.* And for the hardcore, read the original study.
It’s not a perfect study in the way it was designed, but it sure resonates with me. I’ve been annoyed about bogus penicillin allergies since some professor back in medical school mentioned them. It is very frustrating when you know the most effective drug with the least side effects for the patient is penicillin but the patient says:
oh, my mom said when I was little I was allergic to penicillin. Maybe I had a rash or something? I don’t know.
Is it safe to give penicillin anyway, since there’s a low likelihood they have a real allergy? Maybe. Maybe not. We must still be cautious when prescribing penicillin to patients with documented history of reaction, since the initial allergic reaction does not predict the future severity of reaction; many papers indicated this, eg. Correlation of initial food reactions to observed reactions on challenges. A rash isn’t a big deal, but anaphylaxis is!
Realistically, erroneous labelling of penicillin allergy will be less of a problem in future as we become more and more conservative with our antibiotic prescribing. We now know that a lot of the coughs. colds, sore-throats, and ear infections are caused by viruses and health care providers are getting better at educating patients and their families about this fact.
Sometimes an infection is definitely bacterial, and many should be treated with penicillin or one of its close cousins. Usually one can select an alternative medication which should not cause reaction in a penicillin-allergic person, although it will be more expensive, less-specific to the bacteria involved, and probably have more side-effects. However, there is (at least) one illness that must be treated with penicillin. The Centre for Disease Control (CDC) recommends desensitizing patients with allergy to penicillin and then treating with penicillin if they have syphilis (of the neurological, in-pregnancy, or congenital situation. This is of course possible in a monitored setting with allergy-treatment drugs and supportive equipment on-hand.
Syphilis is a scary sexually-transmitted infection (STI aka STD) that can cause bad stuff – even if it is made to look like a big joke on TV:
Ok it’s kind of funny, if you don’t have it! This post isn’t about “The Syph” so you can read about it on your own.
Many people hold bizarre, illogical ideas about allergy (myself included until educated otherwise), but I’ll save my angst about those for another time.