Drug skin tests can reproduce
delayed hypersensitivity to drugs and entail a moderate reexposure of patients to offending drugs.
Drug patch tests (
DPTs) and prick tests can be done with any commercialized form of a
drug. In non-severe delayed non-
IgE-mediated reactions to drugs, intradermal tests (IDT) with delayed readings have a greater value, but their techniques lack standardization. A negative
drug skin test does not exclude the responsibility of a
drug, and the
drug must be rechallenged in non-severe cases.
DPTs are useful in maculopapular rashes, flexural exanthemas, and if done in situ, also in fixed
drug eruption. Their best indication is in
acute generalized exanthematous pustulosis or
drug reaction with eosinophilia and systemic symptoms (DRESS). They should be carried out cautiously, following strict guidelines. Prick tests have a low value but they can sometimes be positive on delayed readings. In non-severe delayed reactions to drugs, intradermal tests with delayed readings are the most sensitive skin tests especially for
beta-lactam antibiotics,
radiocontrast media, heparins but also some
biological agents. The value of patch testing varies according to the implicated
drug and the non-immediate
adverse drug reaction. In DRESS,
DPTs have a good value in testing
carbamazepine or
proton pump inhibitors but remain negative in testing with
allopurinol or
salazopyrin. In
toxic epidermal necrolysis,
DPTs are safe but positive in only 9 to 23 % of the reported cases.