Lori F replied: "Yes!! I developed hives from penicillin when I was in my 30's. I had hives for nine days. Usually benadryl helps, but since you are pregnant you'll have to ask your doctor if you can take it. Tell your doctor right away about the reaction. You probably won't ever be able to take it again. I have to wear a medical alert bracelet stating that I am allergic to penicillin. Good Luck with that and your baby!"

sa_2006 replied: "Allergy to Penicillin Index Incidence Types of Reactions Mechanisms Testing Management Incidence: 2% of all treatments will have systemic reactions. 4% will have urticaria. 0.2% will have anaphylactic shock with a 0.02% mortality. Atopy is not a risk factor and mean age is 20-49 years (Ref.4). Types of Reactions: Reactions may be immediate (within 1 hour) and these manifest mainly as anaphylaxis, urticaria, angioedema or bronchospasm. Accelerated reactions (1-72 hours) manifest mainly as urticaria, but may manifest as erythema multiforme, a maculopapular rash or serum sickness. Late reactions (after 72 hours) usually manifest as morbilliform rashes or fever, but also serum sickness, recurrent urticaria and arthralgia. Mechanisms: Penicillin is a low molecular weight substance which needs to combine with protein to become immunogenic. Major degradation products of penicillin are the BPO (Benzyl penicilloyl) haptenic groups (the major antigenic determinant). One can bind benzyl penicillin to polysine synthetically to form penicilloyl polylysine which is non-immunogenic but can be used to identify penicilloyl specific IgE by skin test (marketed as Pre-Pen but not yet freely available in South Africa). The minor determinants are other degradation products of penicillin which are important causes of anaphylaxis, (MDM is available in Europe). Minor determinants (MDM) may be prepared by diluting fresh and 2 week old Penicillin G, 10 000 units/ml for skin testing purposes. NB: Testing with only major determinants will fail to detect up to 10% of penicillin sensitive subjects. (d) Testing: NB: ALL SKIN TESTING SHOULD BE DONE IN AN EMERGENCY ROOM/ICU SETTING AND PATIENTS SHOULD BE OFF ANTI-HISTAMINES Skin tests with major and minor determinants are predictive of immediate and accelerated reactions to penicillin. Skin prick tests are the first line tests and are followed by intradermal tests. Begin with the polylysine penicilloyl prick tests, followed by an intradermal test. Follow up if negative with a MDM test at diluted concentrations: 1:1000, 1:100, 1:10. A wheal of: 0-3mm = negative 3-5mm = equivocal 5-10mm = positive >10mm = strongly positive False positives occur in 27% and false negatives less than 1%. Only perform intradermal tests if prick tests are negative. The risk of anaphylactic reaction to penicillin is extremely low if skin tests to MDM & PPL are negative. For drugs other than Penicillin G, skin testing can also be performed using diluted drugs (less than 3mg/ml). RAST testing may be done to confirm suspected sensitivity, but false negatives do occur. Management: Avoid b -lactams and cephalosporins in patients with a history of allergic reactions to penicillin. Choose macrolides or cyclines. Remember that penicillin allergy is a variable state and 85% of patients will tolerate penicillin at a later state. Specific skin testing should be performed if clinical indications indicate that Penicillin therapy is absolutely essential. RAST testing will confirm sensitivity. Rarely (e.g. in Subacute Bacterial Endocarditis), it may be necessary to desensitize a patient to penicillin. This can be carefully done within a few hours in ICU according to defined protocols (Ref.2) but should only be performed by a specialist familiar with the technique."