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Skin reactions to heparin are rare, the most frequent manifestation being skin necrosis. Reactions occur either as an isolated manifestation or within a context of heparin-induced thrombopenia. Urticarious and eczematous reaction, either localized at injection sites or with a general distribution, have been recently reported. In all cases, it is mandatory to withdraw heparin therapy. Such accidents can be observed with all types of heparin (standard heparin and low-molecular weight heparin). Cross-reactions between two types of heparin are frequent. Skin tests can be used to guide heparintherapy.

Intolerance to sulfonamides is very frequent in HIV-infected subjects and 10 times more common than in the general population. There are 2 types of intolerance to sulfonamides: early reactions with urticaria or angioedema, which are IgE-dependent, and late reactions with febrile rash, which occur between the 6th and 12th days of treatment and represent the vast majority of allergic manifestations in HIV-infected subjects. Clinically, these reactions resemble serum sickness, but all physiopathological hypotheses point to toxic process. The degradation of sulfonamides has two different pathways: the N-acetylation pathway which is genetically determined and saturable, and the cytochrome P450 pathway which produces toxic hydroxylamine metabolites "detoxified" by glutathione. In HIV-infected subjects detoxication is thought to be incomplete due to an acquired deficiency of glutathione and probably increased in the presence of a slow acetylation profile.

Intradermal tests with 5 muscle relaxants were performed on two occasions in 56 patients who had experienced an adverse event during general anaesthesia: anaphylactoid reaction with at least one positive test 19.5 +/- 13.5 months previously in 50 cases; adverse reaction unrelated to muscle relaxants and with negative tests 21 +/- 6.4 months previously in 6 cases. Sixteen healthy subjects who had never been tested served as controls; their tests were all negative. The reproducibility of 244 assessable tests in the 56 patients reached 88.1%. Twenty-three (9.4%) of the tests previously positive had become negative and six (2.5%) of the tests previously negative had become positive. Tests performed with pancuronium or vecuronium had more often become negative (47% and 40% respectively) than those performed with the other 3 muscle relaxants tested (P less than 0.001). These results suggest that skin tests should be repeated prior to general anaesthesia in all patients who previously developed an anaphylactoid reaction to muscle relaxants.

Skin tests (prick tests) with chymopapain were performed on 3 groups of patients: 75 patients awaiting chemonucleolysis with chymopapain (group I), 42 of these 75 patients 2-3 weeks after chemonucleolysis (group II), and 60 atopic patients suffering from asthma and/or rhinitis with positive skin tests to at least one of the airborne allergens (group III). A positive skin test was found in one patient of group I (1.33%), one patient of group III (1.7%) and 11 patients of group II (26.2%). Thus, sensitization to chymopapain is not more frequent among atopic patients, and chemonucleolysis has a highly significant (P less than 0.001) sensitizing effect. Chymopapain-specific IgE's were found in one out of 75 patients (1.33%) before, and in 14 out of 45 patients (31%) after chemonucleolysis; the difference was significant (P less than 0.001). Concordance between skin tests and specific IgE's reached the 74% level. Our results are consistent with those of the literature. They show that prick tests with a 10 mg/ml solution of chymopapain constitute, for the time being, a simple, reliable and cheap method for detecting subjects at risk.