False-positive tricyclic antidepressant results in diphenhydramine overdose: a report of two cases and a literature review

Our cases and literature review indicate that SIG is prone to yield false positive TCA results in DPH overdose. Considering the increasing incidence of over-the-counter medication overdoses among adolescents in Japan, it is anticipated that there will be more pediatric cases of DPH poisoning in emergency departments. When a TCA-positive result is obtained on SIG, clinicians should consider not only TCA intoxication but also the possibility of DPH overdose. The mechanism of false positives cannot be explained by DPH alone, and the involvement of metabolites is suggested.