Abstracts

Rationale: The diagnosis of antiepileptic drug hypersensitivity is almost entirely based on the basis of a clinically documented reaction. The risk for further adverse events on exposure to the same or related drug is not known. The lymphocyte toxicity assay has been used to assess antiepileptic drug (AED) hypersensitivity and to determine risks associated with resumption of treatment with the offending or related AED. Methods: We assessed the potential positive predictive value of this test among a group of 135 patients evaluated in the regional Adverse Drug Reaction (ADR) clinic. These patients were 1) referred for assessment of adverse events associated with AED therapy and 2) lymphocyte toxicity assay performed in the ADR laboratory. Of these 29 patients were tested for adverse drug reactions to AED’s. Results: Twenty-nine lymphocyte assays were considered positive for anticonvulsant toxicity, primarily to carbamazepine (n=12, 47.38%), phenytoin (n=12, 47.38%), phenobarbital (n=2, 6.9%), primidone (n=2, 6.9%), and valproic acid (n=1, 3.5%). Eleven of 29 positive assays (37.9%) showed cross reactivity to two or more AED’s. Two patients with a negative test were rechallenged and tolerated therapy. One patient with a positive test was also re-challenged,and tolerated therapy. Clinicians were reluctant to re-challenge patients with a history of an anticonvulsant adverse reaction despite a negative test. Conclusions: The clinical application of the results of a lymphocyte toxicity assay carried out following the investigation of an AED related adverse drug reaction presents challenges to the clinician . While a positive test may confirm a specific anticonvulsant adverse reaction, a negative test opens up the possibility of a rechallenge, the limitations and challenges to the clinical utility of this assay remain to be defined, such as the positive and negative predictive value of the assay.