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Fernando and Broadfoot raise interesting points with respect to the potential value of pharmacogenetic screening for prevention of severe adverse drug reactions as well as the possibility of a potential common pathophysiology of drug hypersensitivity syndrome.1 There are conflicting theories as to the pathogenesis of drug hypersensitivity syndrome. The reactive metabolite hypothesis assumes elevated concentrations of toxic reactive drug metabolites serve as the syndrome trigger and has led to clinical applications, including testing potentially hypersensitive patients with the lymphocyte toxicity assay and the in vitro platelet toxicity assay.
We have used both assays to test a patient of Han Chinese origin who is HLA-B*1502 positive and developed Stevens–Johnson syndrome (SJS) after starting a course of carbamazepine (CBZ). The test was negative three and nine months after patient recovery, despite a typical CBZ-SJS reaction. At the same time, the test was positive in a patient who developed a nonbullous type of drug hypersensitivity syndrome to carbamazepine. This finding strongly suggests that carbamazepine-induced severe bullous reactions have different underlying pathophysiology than carbamazepine-induced nonbullous reactions. We agree that genetic testing of potential drug hypersensitivity syndrome patients could be a useful approach to minimize morbidity and mortality of such reactions. However, we believe that until a clear understanding of this disorder’s pathophysiology is available, a robust cause–effect relationship between such genetic markers and the disease is not achievable.
For the full letter, go to: www.cmaj.ca/cgi/eletters/182/5/476#318339