Pearls of Wisdom: A Drug Test Unexpectedly Positive for Methadone
Tom, a 56-year-old house painter, fell off a ladder and fractured 3 ribs. He was prescribed tramadol for pain relief. A few days later, the results of a urine drug test came back positive for methadone, but Tom said that he had never taken methadone.
What is the explanation?
A. The patient was lying; false-positive methadone test results are very rare.
B. The tramadol he was taking for pain caused false-positive methadone test results.
C. The quetiapine he was taking for depression caused false-positive methadone test results.
D. Endogenous opioids induced by acute pain caused false-positive methadone test results.
What is the correct answer?
(Answer and discussion on next page)
Louis Kuritzky, MD, has been involved in medical education since the 1970s. Drawing upon years of clinical experience, he has crafted each year for almost 3 decades a collection of items that are often underappreciated by clinicians, yet important for patients. These “Pearls of Wisdom” often highlight studies that may not have gotten traction within the clinical community and/or may have been overlooked since their time of publishing, but warrant a second look.
Now, for the first time, Dr Kuritzky is sharing these pearls with the Consultant360 audience. Sign up today to receive new advice each week.
Answer: The quetiapine that the patient was taking for depression caused false-positive drug test results for methadone.
The fact that quetiapine (Seroquel) can cause false-positive drug test results has only recently been revealed.
The Research
In a 2010 article, a group of authors followed the cases of 10 inpatients taking quetiapine who all tested positive for methadone but who all denied using the drug.1 The 10 inpatients had been monitored 24/7 in a hospital psychiatric ward. For such a large number of patients to have surreptitiously acquired methadone would require quite a leap of imagination. Hence, it was accepted that the patients' attestations denying methadone use, coupled with the protected setting, seemed sufficient to exclude any possible methadone ingestion.
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The Results
The researchers followed up the initial urine drug tests (the ones with unexpectedly methodone-positive results) with more-sophisticated gas chromatography–mass spectrometry testing, and the results were negative for methadone in each of the 10 patients. This means that these patients did not have methadone in their blood, despite the apparently positive urine test results.
What’s the "Take-Home?"
If your patients' urine drug test results come back positive for methadone, the researchers strongly recommended confirming the results with a second method, particularly in patients who are taking quetiapine.
Reference:
1. Fischer M, Reif A, Polak T, Pfuhlmann B, Fallgatter AJ. False-positive methadone drug screens during quetiapine treatment. J Clin Psychiatry. 2010;71(12):1696. doi:10.4088/JCP.10l06044yel.