Our first step in evaluating your child for a suspected allergy to a medication is to obtain a careful history. If we suspect and allergic reaction, we may offer allergy testing and challenge. For some medications, such as penicillin, skin testing has been well studied. For other medications, testing has not been well studied, and the results of testing are less reliable or testing cannot be even be performed.
In general, positive testing is considered confirmation of the allergy, and the drug should be avoided in the future. Negative testing never 100 percent rules out the allergy, and the drug needs to be given again to prove that your child is not allergic. This is usually done under observation in a physician's office. Depending on the previous reaction, the drug may be given in several small doses or all at once. Your child is then monitored for a period of time (45 minutes to several hours, depending on his history). In some cases, a delayed reaction is suspected, and the drug may be continued at home for a short period.
For the challenge procedure, your child should be healthy, with no fever, rash or significant respiratory illness. For both skin testing and challenge, antihistamines cannot be give for 72 hours prior to the appointment so as not to cover up a reaction. For more information on antihistamines to avoid before testing, see our Antihistamine Avoidance list.