300 Longwood Avenue Boston, MA 02115 (617) 355-6000 My Child Has: Antibiotic Allergy Testing Programs that perform this test Allergy Program   Allergy testing for antibiotics is indicated when there has been an allergic reaction while taking an antibiotic. Standardized skin testing is available for penicillin. Skin testing for other antibiotics such as cephalosporins can be done but the validity is uncertain. No routine skin testing is available for sulfa drugs (found in Bactrim or Septra) erythromycin, or clindamycin. Appointment preparations Testing will take a total of two to four hours. Because much of the time will be spent waiting in between procedures, feel free to bring a game, book, snacks or other special diversions as appropriate for you and your child. Antihistamines will interfere with the skin test results. For this reason, no prescription or over-the-counter antihistamines can be taken for one week before testing. Antihistamines are found in many over-the-counter cold remedies. Some common products containing antihistamine include: Actifed, Dimetapp, Pediacare and Triaminic cold formulas, Benadryl, and Claritin, as well as many others. Patients on Hismanal need to stop it at least 6 weeks before testing. Please check with your doctor or nurse if you are unsure about your medication. Testing There are three or four stages of testing with 10-20 minutes in between each stage. For penicillin testing, four components are needed (penicillin, pre-pen, minor determinant mixture and ampicillin). With each advancing stage, an increasing concentration of antibiotic is used. The testing starts with a very dilute concentration to make sure allergic reactions do not occur. If your child has a positive skin reaction to one of the components at any stage in the testing it is not necessary to test with that specific component any further (since we know your child is allergic). The first stage is the skin prick testing. On the inner aspect of the forearm several drops (including a histamine and saline control) are placed on the skin with a device that has eight receptacles. Each one has prongs similar to the TB prick test. Some children have described prick testing as a hairbrush being lightly pressed onto the arm. It is necessary that the histamine drop react in order for the testing to continue. A positive reaction is a small hive with some redness that may feel itchy. This means your child does not have antihistamines in his/her system which would block positive test results. This is the only 10-20 minute period your child needs to keep his/her arm still. After 10-20 minutes the nurse will check the arm for any positive results. It is unusual to react to the antibiotics at this point. In the next stages the antibiotic is placed under the top layer of skin (intradermal) on the back of the upper arm with the tip of a small needle. The antibiotics are diluted for the first stage and are tenfold more concentrated for each progressive stage. After 10-20 minutes the nurse will check for a positive reaction which is an enlarged hive and possibly redness. Positive skin test reactions will gradually disappear over a period of 30-60 minutes, and usually, no treatment is needed. At times a low potency topical steroid cream will be applied to reduce the itching and redness. Occasionally local swelling and itching occurs at a skin test site four to eight hours after the testing. These delayed reactions are not serious and will disappear over the next several days. Any reactions should be measured and reported to the nurse or doctor at your next visit. If your child has a fever, or is having an increase in allergy or asthma symptoms, testing will probably need to be rescheduled. If you have any questions regarding the appointment, testing, etc., please call one of Children's allergy nurses at 617-355-6117 between 8:30 am and 4:30 pm Monday-Friday. The information on this website should not be taken as medical advice, which can only be given to you by your personal health care professional. Copyright © Children's Hospital Boston. All rights reserved.