Type IV hypersensitivity to oral nystatin

[Drug patch tests in the investigation of cutaneous adverse drug reactions]

Cutaneous adverse drug reactions (CADR) are a frequent problem in clinical medicine. Since patients are often on multiple drug regimes, it is often difficult to pinpoint the relevant drug from history alone. Besides clinical and chronological parameters, patch testing with the suspected compound has been reported as helpful in determining the cause of a CADR and in studying the physiopathological mechanisms involved in such reactions. The key advantage of drug patch tests is that they can be performed using any commercialized form of drugs and without hospital surveillance because they only rarely induce adverse reactions, which in any event are mild. The method for performing drug patch tests has been described, and requisite commercialized material is now commercially available, failing which the best approach is to dilute the drug in its commercialized form at 30% in petrolatum or in water. The results of drug patch tests depend on the drug tested and the clinical features of the initial CADR. They appear to be of value in investigating maculopapular rash, eczema at drug injection sites, photosensitivity (photopatch tests with 5J of irradiation), fixed drug eruption (testing at the sequelae site), acute generalized exanthematous pustulosis and symmetrical drug-related intertriginous flexural exanthema. Although less widely used, they are probably also of value in drug reaction with eosinophilia and systemic symptoms (DRESS) but they are of less use in Stevens-Johnson syndrome (SSJ) and Lyell's syndrome. Many drugs have been reported as producing positive patch tests, and most of these are summarized in a summary table of this literature review.

Drug patch testing in systemic cutaneous drug allergy

Patch testing with the suspected compound has been reported to be helpful in determining the cause of a cutaneous adverse drug reaction (CADR) and in studying the pathophysiological mechanisms involved. The main advantages of drug patch tests are that they can be done with no hospital surveillance because they induce only rarely adverse reactions and that any commercialized form of a drug can be used. In contrast, intradermal tests can be performed only with injectable forms or with a pure and sterile form of the drug. It is advised to perform drug patch tests during the 6 months following the CADR as we do not know whether positive results will persist. Due to the possibility that a low concentration might yield false negative results, drug patch tests have to be performed with rather high concentrations of the commercialized form of the drug, mostly diluted at 30% in petrolatum and/or in water. For some drugs and severe CADR, it is necessary to tests with lower concentrations or in other vehicles. Drug patch tests are positive in ca. 32-50% of patients who have developed a CADR. The clinical relevance of drug patch tests depends on the clinical features of the CADR (valuable in testing generalized eczema, systemic contact dermatitis, maculopapular rash, acute generalized exanthematous pustulosis, fixed drug eruption) and on the involved drug. As false positive results can be observed, it is always necessary to consider the relevance of any positive drug patch test. Their specificity and their negative predictive value have not been yet determined.