Evaluation of tricyclic antidepressant false positivity in a pediatric case of cyproheptadine (periactin) overdose.

CASE REPORT: The authors report a case of pediatric cyproheptadine toxicity, initially misdiagnosed as tricyclic toxicity based on the results of a preliminary rapid toxicological serum screen. Although such cross-reactivity has been reported, the chemical basis of this observation has not yet been evaluated. By GC/MS methods and HPLC assays adapted for the detection of tricyclic compounds, the authors confirmed that cyproheptadine was indeed responsible for this patient's toxicity. In addition, the authors identified the presence of a cyproheptadine metabolite in the patient's serum. Further testing in an immunoassay-based toxicologic screen demonstrated some cross-reactivity exhibited by the patient's serum, but not the parent compound. These findings showed that the cross-reactivity correlated with the presence of the cyproheptadine metabolite, highlighting the value of confirmatory toxicologic testing of routine rapid toxicologic screens.