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Reactions to antibiotics: What you need to know

Drug reactions, sometimes caused by an allergy, range from mild to severe, and may occur right away or several weeks after taking the medicine.

When there is a question about possible allergy to antibiotics such as penicillin and amoxicillin, it is important to narrow down the many types of adverse reactions that may have occurred. The spectrum of medication reactions is broad and includes common side effects, intolerances and toxicities, with allergies making-up only a small portion of all reactions. Drug reactions range from mild to severe, and may occur right away or several weeks after taking the medicine.

The first step in classifying a reaction is to figure out if the cause is related to the child's immune system. This can be accomplished by an experienced health care provider taking a careful history about the reaction. If the reaction is thought to be due to the immune system, then it is considered to be an allergy. For example, if a child receives amoxicillin and develops diarrhea without other symptoms, the child most likely experienced an adverse reaction that was not caused by the immune system, and so, this reaction is not classified as an allergy.

On the other hand, if a child develops hives and trouble breathing minutes after receiving penicillin, this is more likely due to an immune response and therefore, the reaction would be called a drug allergy. The next step in describing a drug allergy is to decide if the reaction was immediate, or occurring within about an hour of taking a dose of the medicine, or delayed, which can occur several hours or more after the dose is taken. Even if a reaction is delayed, it might still be a drug allergy.

About 5 to 10 percent of patients report a history of allergy to penicillin drugs, however, studies show that up to 90 percent of these people will have negative allergy testing for the drug and will actually be able to tolerate the medication without a reaction. One of the reasons for this discrepancy is the wide array of rashes that can occur when a patient is ill. Sometimes, a rash might be due to the drug, but more often, the rash is related to the illness itself. Allergists are skilled at making this difficult distinction. Depending on the type of rash, allergists can perform special testing that can help to confirm whether someone is allergic to penicillin. If you or your child has been diagnosed with an allergy to penicillin due to a rash, it would likely be helpful to see an allergy specialist for further evaluation.

Another reason a child might be described as allergic to penicillin is due to a family member having an allergy to the drug. However, it is not necessary for children with a family history of penicillin allergy to avoid this drug or related antibiotics, as they are not considered to be allergic themselves.

It is also important to keep in mind that people typically outgrow penicillin allergy. In fact, after five years, about 50 percent of patients with penicillin allergy will be able to tolerate the drug. In 10 years, that number jumps to 80 percent. If several years have passed since the reaction, you can consider having your child evaluated by an allergist to find out if the drug allergy may have resolved.

If a child is truly allergic to an antibiotic and that drug is the best medication to treat a certain infection, desensitization is a technique that allergists can use in some instances. This procedure allows the child to safely take the antibiotic temporarily. To achieve desensitization, a drug is given in progressively increasing doses over several hours. This causes the immune system to go into a state of temporary tolerance for as long as the medication is continued. Once the drug is stopped, however, the allergy returns and the drug needs to be avoided. This procedure can be used for penicillin and other antibiotics. For example, in our clinic, we have successfully used this technique for a child with Lyme disease and amoxicillin allergy, since in this case, amoxicillin was the preferred treatment. Keep in mind though that desensitization should only be performed by an allergist and will not be appropriate for all types of drug allergy.

Finally, while many patients who report penicillin allergy may have had a non-allergic reaction, a rash due to an infection rather than a drug, or may have outgrown the diagnosis, reactions to medications can be quite severe and life-threatening in some cases. For this reason, if you or your child has been diagnosed with a drug allergy, the medication should be strictly avoided until further evaluation is completed by an allergist.

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