False positive fentanyl immunoassay in the setting of chronic loperamide misuse: A case report

Loperamide and its metabolites can induce false positive readings for fentanyl and buprenorphine on urine drug assays when misused at high concentrations. We present a 30-year-old male with spinal muscular atrophy type II who presented with altered mental status and was found to have sepsis secondary to pneumonia and chronic high-dose loperamide misuse. Initial urine toxicology screening was falsely positive for fentanyl. Clinical findings included QTc prolongation and elevated lipase, both suggestive of loperamide toxicity. The patient’s symptoms improved with supportive care, cessation of loperamide, and empiric antibiotics. This case highlights the potential for high-dose loperamide use to interfere with urine drug screening assays and underscores the need for increased clinical awareness of its toxicities and diagnostic implications.