Quetiapine and False-Positive Urine Drug Testing for Tricyclic Antidepressants

Mr. A was a 34-year-old, white male veteran with a history of previous treatment-refractory schizoaffective disorder and amphetamine dependence who was admitted to the hospital for an exacerbation of his depressive and psychotic symptoms. He also reported episodes of irritability, racing thoughts, increasing goal-directed activity, and insomnia, but the differential diagnosis between his amphetamine use and a manic component to his schizoaffective disorder had never been clarified. His only prescribed medication at the time of his admission was quetiapine, 600 mg/day.

At Mr. A’s hospital admission, a urine sample was submitted for routine toxicology testing, including analysis for amphetamines, barbiturates, benzodiazepines, cannabinoids, cocaine metabolites, opiates, methadone, alcohol, and tricyclic antidepressants. The results showed a positive toxicology screening for tricyclic antidepressants, whereas the other toxicology assays on the specimen were all negative. Mr. A denied using tricyclics, but given the possibility that surreptitious use of that drug class might be materially contributing to his ongoing clinical symptoms (1), it was important to rule out drug interference in the assay.