Medication allergies

October 2, 2002

I've seen patients develop wheezing and hives within an hour after taking penicillin. But often the only symptom of possible allergy to a medication is a rash that develops, sometimes near the end of therapy.

Usually any rash that develops during or soon after a course of treatment with antibiotics or other new meds is highly suspicioned as being an allergy to that drug. Medication allergies can be fatal. If there is any doubt as to whether it is an allergy to the medication, most physicians will consider it a drug allergy so the medication is not given again.

I often heard a well-respected dermatologist I worked with say, "A person can suddenly develop an allergy to a medication they have taken all their life," and I have seen that happen. Sometimes it is difficult to know for sure if the medication caused the reaction, but usually a rash that develops from a medication lasts only a few days after the medication is discontinued, especially when antihistamines are used to treat the rash. Anytime a rash lasts longer than a few days after stopping the drug, other possible causes of the rash should be investigated.

Here are links to other questions we've answered regarding rashes and medication allergies:

What is this skin rash?

Penicillin, antibiotic, and medicaiton allergy

Am I allergic to penicillin?

You can also do a search on "hives" or "urticaria" from the search form at the top left for more information.

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