Skin tests drug allergy

Ozanguc N. Nonpigmenting solitary fixed drug eruption after skin testing and intra-articular injection of triamcinolone acetonide. Ann Allergy Asthma Immunol... 

Simple patch skin testing is naturally most useful in diagnosing contact dermatitis, but it is unreliable for other allergies. Skin prick tests are helpful in specialist hands for diagnosing IgE-dependent drug reactions, notably due to penicillin, cephalosporins, muscle relaxants, thiopental, streptokinase, cis-platin, insulin and latex. They can cause anaphylactic shock. False positive results occur. 

Two cases of drug allergy have been reported in a 37-year-old woman and a 66-year-old man, who received hydroxyzine for premedication before anesthesia (1,2). In these patients immediate skin tests with the implicated drug were positive. 

Leynadier F, Dry J. Anaphylaxis to muscle-relaxant drugs study of cross-reactivity by skin tests. Int Arch Allergy Appl Immunol 1991 94(l ) 349-53. 

Mechanisms of non-immediate reactions are unclear but may be immunological and non-immunological. Delayed reactions of the IgE type are known (131). Aminopenicillins seem to be an important cause of non-immediate reactions (132-134). The morbilliform rash that begins 1-10 days after amoxicillin can be caused by a delayed cell-mediated immune reaction (135) as can fixed drug eruptions (136,137), toxic epidermal necrolysis (138-140), bullous erythroderma (141), and contact eczema (142). Investigation of these disorders should include delayed readings of skin tests (135). In patients with chronic urticaria, penicillin allergy was demonstrated by cutaneous tests. 

III. Contraindications. No contraindications are known. Caution is warranted in patients with known sensitivity to ovine (sheep) products a skin test for hypersensitivity may be performed in such patients, using diluted reconstituted dmg. There are no reports of hypersensitivity reactions in patients who have received the drug more than once (although a theoretical risk). Product may contain traces of papain therefore, caution is advised in patients with allergies to papain, chymopapain, papaya extracts, and the pineapple enzyme bromelain. 

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