Patch testing with carbamazepine and its main metabolite carbamazepine epoxide in cutaneous adverse drug reactions to carbamazepine.

The value of skin tests in the diagnosis of adverse drug reactions (ADRs) has been limited. Lack of knowledge as to the nature of drug allergens has contributed to these limitations. Several reports have addressed the roles of metabolites in cutaneous ADRs and skin testing. We evaluated the role of a carbamazepine (CBZ) metabolite on the results obtained from patch tests, using CBZ and its main metabolite 10, 11-epoxide of CBZ (CBZ-epoxide), on 13 patients with CBZ-induced drug eruptions and 39 controls with no CBZ-induced cutaneous ADRs. 10 of the 13 patients showed a positive reaction, and 2 of the 10 patients had a reaction to the CBZ-epoxide only and 1 to both CBZ and CBZ-epoxide. None of the 39 controls displayed any reactions to either CBZ or CBZ-epoxide. Patch testing of suspected drugs, as well as their available metabolites, would be helpful in improving the results.