However, studies using skin testing for penicillin allergy have found that about 90 percent of those with penicillin allergy on their health records are not allergic to penicillin. In other words, about 1 percent of the population is allergic — not 10 percent.
Allergic reactions to penicillin also can go away with time. Penicillin-based drugs, which are prescribed commonly, are an important class of antibiotic. It is when the immune system produces an exaggerated or inappropriate response that does not normally in occur in most other people.
Symptoms and signs are usually rapid in onset, i. Delayed immune reactions can occur several days after antibiotic treatment is begun, and are generally mediated by T-cells IgG-mediated. More serious delayed immune reactions generally involve rash in conjunction with systemic symptoms, including: 3. Adverse effects are the undesirable but predictable symptoms and signs associated with the pharmacological action of a medicine, e.
Intolerance is a sensitivity reaction to a medicine that does not involve the immune system. It is dependent on both the pharmacological action of the medicine and patient susceptibility factors. Viral infection is a common cause of rash , particularly in children, e. Allergy to an antibiotic occurs after a person has had an initial exposure which can include in utero exposure and has become sensitised. Therefore prior tolerance of an antibiotic does not provide evidence that a person is not allergic.
Penicillin is the most frequent antibiotic class allergy and penicillin G [benzylpenicillin] the most frequent allergy among penicillins , followed by sulfonamides and tetracylines. Parenteral administration of an antibiotic is associated with a higher risk of allergic reaction than oral administration. Allergy to antibiotics most commonly occurs between age 20 — 49 years. A small study analysed risk factors in 62 patients who attended allergy clinics in the United States, of whom 23 had documented penicillin allergy and 39 were age, gender and ethnicity matched controls who had tolerated penicillin.
Multivariate analysis showed that a history of penicillin allergy in a first-degree relative and a history of allergy to other medicines were significant risk factors for penicillin allergy. Penicillin allergy was associated with a history of atopy, but this was not statistically significant in the multivariate model. Further research is needed in this area to provide definitive answers. If a patient has a convincing history of an allergic reaction to an antibiotic, there is no need for laboratory investigation; allergy is established and laboratory confirmation of this would not change management.
If the patient has an uncertain history, it is in theory possible to test for antibiotic allergy, however, testing is not available for all antibiotics and when it is available, results need to be interpreted appropriately. Most patients who are allergic to penicillin are not allergic to the whole molecule; instead, their reaction is to degradation products of penicillin bound to self-carrier proteins. The negative predictive value of this test is very high, with no serious reactions reported in patients who were negative on testing who then underwent penicillin challenge.
Some hospitals will perform supervised antibiotic challenges on all patients with negative skin prick or intradermal tests. Some providers may offer skin prick or intradermal testing for cephalosporin allergy.
Testing for other antibiotics is not usually available. If laboratory testing for antibiotic allergy is being considered, it is strongly recommended to discuss an appropriate approach to testing with the local laboratory or relevant specialist. If the patient has a history of an acute IgE-mediated hypersensitivity reaction after taking an antibiotic, it can be assumed that this reaction is likely to occur again on re-exposure.
In most cases alternative classes of antibiotics will be available and can be used instead. Desensitisation protocols can be carried out under specialist supervision in a hospital setting to induce temporary tolerance to an antibiotic if it is required for treating a serious infection, e.
People with an allergy to one antibiotic may react to structurally similar antibiotics. It is sometimes possible to predict cross-reactivity on the basis of the structure of the drug and, if known, what the person is specifically allergic to, e. Cross-reactivity to cephalosporins in patients allergic to penicillin does occur, but it is thought that this risk is very low. If the patient has a history of a delayed hypersensitivity reaction after taking an antibiotic, re-challenge may be possible, depending on the nature of the reaction.
Patients with an IgE-mediated drug allergy or a serious non-IgE-mediated reaction should be encouraged to wear a medic alert emblem. If the patient has a history of intolerance or adverse effects after taking an antibiotic, it depends on the nature of the symptoms or signs as to whether this is a contraindication for taking the medicine in the future. Patients who have experienced a serious adverse effect after taking an antibiotic, e. Conversely, the benefits of treatment with a particular antibiotic and lack of availability of other suitable options may outweigh the risk of recurrence of adverse effects in patients who have experienced less severe adverse effects, e.
Advertising revenue supports our not-for-profit mission. This content does not have an English version. This content does not have an Arabic version. Overview Penicillin allergy is an abnormal reaction of your immune system to the antibiotic drug penicillin. Drug rash Open pop-up dialog box Close. Drug rash A drug rash usually starts within two weeks of taking a new medication and begins as discrete red spots that spread, covering large areas of the body. Request an Appointment at Mayo Clinic.
Share on: Facebook Twitter. Show references Shenoy ES, et al. Evaluation and management of penicillin allergy. Journal of the American Medical Association. Accessed Oct. Drug allergies. Kufel WD, et al.
Penicillin allergy assessment and skin testing in the outpatient setting. Solensky R. Penicillin allergy: Immediate reactions. Merck Manual Professional Version.
Penicillin allergy: Delayed hypersensitivity reactions. Pongdee T, et al.
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