B-299 Selegiline Metabolism Mimicking Illicit Drug Use: A Case of Amphetamine-Positive Meconium

Background Immunoassays are commonly used in clinical settings for rapid drug screening, yet they are prone to cross-reactivity and interference from medications and substances, leading to false-positive results. Because of this, follow up confirmatory testing by either liquid chromatography-mass spectrometry (LC-MS) or gas chromatography-mass spectrometry (GC-MS) is highly recommended. An infant*s meconium tested positive for amphetamine and methamphetamine by mass spectrometry but mother denied substance abuse and claimed to be taking selegiline for anxiety. The clinical implications of differentiating between amphetamine misuse versus a prescribed medication are significant, particularly during and after a pregnancy where a positive result may trigger a newborn risk assessment which could lead to a report to child protective services. This case highlights the need to understand potential cross-reactivity of medications with drug screening and confirmation testing methods. Methods We analyzed the case of an infant, exploring the biochemical pathway of selegiline and its potential to produce metabolites that can lead to a positive amphetamine result by either immunoassays and/or mass spectrometry. Mass spectrometry testing on meconium of the infant was performed at a send out reference laboratory. A literature review was conducted to identify other medications and substances that commonly cause cross-reactivity in immunoassays. Some general findings are synthesized into the table. Results Results of a drug screen on the meconium came back positive for amphetamine and methamphetamine when analyzed by mass spectrometry, this sparked concern with the medical team. Selegiline is metabolized into l-methamphetamine and l-amphetamine. The mass spectrometry method did not distinguish between (d) and (l) amphetamine/methamphetamine, it was concluded that the observer results could be from selegiline metabolism. A review of the literature revealed numerous medications and substances that interfere with immunoassay drug screens as shown in Table 1. Conclusion This case underscores the critical importance of confirmatory testing and clinical correlation in drug screening/confirmation, particularly in sensitive cases such as pregnancy. Understanding drugs of abuse screen and confirmation procedures, and potential agents that can cause positive results is crucial to prevent misdiagnosis and unnecessary interventions, safeguarding patient care.