immunology allergic disorders
Drug Hypersensitivity
Diagnosis of Drug Hypersensitivity
Patient’s report of a reaction soon after taking a drug Skin testing Sometimes drug provocation testing Sometimes direct and indirect antiglobulin assays The following can help differentiate drug hypersensitivity from toxic and adverse drug effects and from problems due to Drug Interactions . Time of onset Known effects of a drug Results of a repeat drug challenge For example, a dose-related reaction is often drug toxicity, not drug hypersensitivity. Drug hypersensitivity is suggested when a reaction occurs within minutes to hours after drug administration. However, many patients report a past reaction of uncertain nature. In such cases, if there is no equivalent substitute (eg, when penicillin is needed to treat syphilis), testing should be considered. Tests for Type I help identify reactions to beta-lactam antibiotics, foreign (xenogeneic) serum, and some vaccines and polypeptide hormones. However, typically, only 10 to 20% of patients who report a penicillin allergy have a positive reaction on skin tests. Also, for most drugs (including cephalosporins), skin tests are unreliable and, because they detect only IgE-mediated reactions, do not predict the occurrence of morbilliform eruptions, hemolytic anemia, or nephritis. are used with histamine and saline as controls. The Specific tests is used first. If patients have a history of a severe anaphylactic reaction, reagents should be diluted 100-fold for initial testing. If prick tests are negative, intradermal testing may follow. If skin tests are positive, patients should be given Forxenogeneic serum skin testing,patients who are not atopic and who have not previously received xenogeneic (eg, horse) serum should first be given a prick test with a 1:10 dilution; if this test is negative, 0.02 mL of a 1:1000 dilution is injected intradermally. A wheal>0.5 cm in diameter develops within 15 minutes in sensitive patients. Initially, for all patients who may have previously received serum—whether or not they reacted—and for those with a suspected allergic history, a prick test should be done using a 1:1000 dilution; if results are negative, 1:100 is used, and if results are again negative, 1:10 is used as above. A negative result rules out the possibility of anaphylaxis but does not predict incidence of subsequent serum sickness. For drug provocation testing, a drug suspected of causing a hypersensitivity reaction is given in escalating doses to precipitate the reaction. This test is usually safe and effective if done in a controlled setting. Because drug hypersensitivity is associated with certain human leukocyte antigen (HLA) class I haplotypes, genotyping of patients from particular ethnic groups can identify those at higher risk of hypersensitivity reactions. Tests for hematologic drug reactions include Diagnosis . Tests for other specific drug hypersensitivity (eg, allergen-specific serum IgE testing, histamine release, basophil or mast cell degranulation, lymphocyte transformation) are unreliable or experimental. 