Trip Answers

Question answered:20/03/08

We found little robust information to answer this question.

 

However, an article on anaphylaxis to penicillins after non-therapeutic exposure begins by stating:

 

“There is no doubt that the penicillins are an extremely useful class of antibiotics with a very low level of toxicity. However, it is also true that a small proportion of patients become sensitized when treated and can then develop allergic reactions on subsequent exposure, which in a small number of cases can be anaphylactic with life threatening consequences…” [1]

 

A patient information leaflet produced by the Mayo Clinic notes:

 

“You aren't born allergic to penicillin, but you can develop penicillin allergy once you've been exposed to the drug. After that, re-exposure to penicillin or related antibiotics can trigger an allergic reaction.” [2]

 

The John Hopkins Hospital website has a page on medication allergy and side-effects on which it discusses how to differentiate between both reactions:

 

“Is It a Medication Allergy or a Side Effect?
Although it may be difficult to tell the difference between an allergic reaction, a side effect and an idiosyncratic reaction, here are some tips.
• An allergic reaction to a medication never occurs on the first exposure to it, but it can occur even with small amounts of the medication at any subsequent exposure.
The reaction to a particular medication will usually be of the same type in every instance, be it a rash, itching, abdominal complaint or respiratory symptom; however, the severity of the symptoms may vary.
• A side effect is an undesirable but known action of a medication that is most often uncovered during clinical testing of the drug. Whether or not the side effect occurs often depends on the strength of the dose; the larger the dose, the more likely it will cause a side effect. That means that, unlike with a true allergy, you may not experience the unpleasant effect at a lower dose.
• An idiosyncratic reaction, unlike allergy, can occur on first exposure to the medication. And unlike a side effect, the reaction occurs only in susceptible individuals, presumably due to a genetic or metabolic abnormality.” [3]

 

References
1. Blanca M, Garcia J and Vega J et al. Anaphylaxis to penicillins after non-therapeutic exposure: an immunological investigations. Clinical and Experimental Allergy, 1996, Volume 26, pp. 335-340. (http://www.blackwell-synergy.com/doi/pdf/10.1111/j.1365-2222.1996.tb00100.x)
2. Mayo Clinic. Pencillin allergy. 2004. (http://www.mayoclinic.com/health/penicillin-allergy/DS00620/DSECTION=3)
3. JHU. Is It a Medication Allergy or a Side Effect? 2002 (http://www.hopkinshospital.org/health_info/Allergy_Asthma/Reading/med_allergy.html)

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