A false positive fentanyl result on urine drug screen in a patient treated with ziprasidone

The objective of this case report is to highlight the possibility of the second-generation antipsychotic ziprasidone causing a false positive result for fentanyl on a urine drug screen (UDS). A 70-year-old female was admitted to an inpatient psychiatric unit for treatment of a manic episode of bipolar I disorder. She had no previous history of a substance use disorder (SUD) and had no previous positive results on UDS tests spanning an 8-year period. However, her UDS obtained in the emergency department (ED) was positive for fentanyl. The patient adamantly denied that she had ingested anything other than her prescribed medications. Her outpatient psychiatric provider also endorsed that she had no previous known history of an SUD. It was suspected that the patient’s treatment with ziprasidone prior to admission and in the ED contributed to this positive fentanyl result. It has been established that risperidone may cause false positive fentanyl results on UDS. Due to structural similarities, ziprasidone may also cause this same result. As clinicians become more aware of the ubiquity of fentanyl in the illicit drug supply, it is imperative that clinicians also consider limitations of the currently available UDSs.