Drug hypersensitivity may deprive patients of drug therapy, and occasionally no effective alternative treatment is available. Successful desensitization has been well documented in delayed drug hypersensitivity reactions. In certain situations, such as sulfonamide hypersensitivity in HIV-positive patients or hypersensitivity to antibiotics in patients with cystic fibrosis, published success rates reach 80%, and this procedure appears helpful for the patient management. A state of clinical tolerance may be achieved by the administration of increasing doses of the previously offending drug. However, in most cases, a pre-existent sensitization has not been proven by positive skin tests. Successful re-administration may have occurred in nonsensitized patients. A better understanding of the underlying mechanisms of desensitization is needed. Currently, desensitization in delayed hypersensitivity reactions is restricted to mild, uncomplicated exanthems and fixed drug eruptions. The published success rates vary depending on clinical manifestations, drugs, and applied protocols. Slower protocols tend to be more effective than rush protocols; however, underreporting of unsuccessful procedures is very probable. The decision to desensitize a patient must always be made on an individual basis, balancing risks and benefits. This paper reviews the literature and presents the expert experience of the Drug Hypersensitivity Interest Group of the European Academy of Allergy and Clinical Immunology.Drug hypersensitivity reactions account for more than 15% of all adverse drug reactions and are an important problem in clinical medicine. Drug hypersensitivity reactions may be allergic or nonallergic. Allergic reactions are IgE-or non-IgE-mediated (1). They have also been classified into immediate and nonimmediate (2). Immediate drug hypersensitivity reactions occur within 1 h after drug exposure and can be IgE-mediated or linked to a nonspecific histamine release. Nonimmediate or delayed reactions manifest after more than 1 h. In some of these reactions, a T-cell-mediated Allergy 68 (2013) 844-852

Non-immediate hypersensitivity reactions to antibiotics in patients with CF represent a real-life challenge for clinicians. Desensitization is often performed in patients who have exhausted all therapeutic options. Whilst desensitization is an established procedure for immediate reactions we assessed the outcomes and safety of desensitization for non-immediate reactions. We retrospectively reviewed 275 desensitization procedures in 42 patients with a range of non-immediate reactions to six commonly used antibiotics. Desensitization was performed using a 7-step rapid intravenous protocol on a normal medical ward. 250 (91%) of overall desensitization procedures were successful; however, this figure incorporates certain individuals having multiple successful procedures. Individual patient success ranged from 55% with tazocin through to 88% with tobramycin. In the 25 patients who failed desensitization the reactions were mild and the majority occurred within 48 h of starting treatment. Prophylactic anti-histamines and steroids did not reduce the risk of reaction. Whilst the mechanisms remain uncertain we can confirm that rapid desensitization is a safe and effective way of re-introducing an antibiotic to a patient with a non-immediate reaction.