A 63-year-old man comes to the office for routine follow-up a month after being prescribed morphine for chronic, treatment-resistant back pain. The patient says that his pain is greatly reduced since starting the morphine. He has been able to begin a light exercise regimen for the first time in over 2 years. His other medical conditions include hypertension, type 2 diabetes mellitus, allergic rhinitis, and major depressive disorder. Temperature is 36.1 C (97 F), blood pressure is 118/84 mm Hg, pulse is 62/min, and respirations are 12/min. The patient has normal range of motion of the spine, and movement is associated with a reduction in pain compared with previous examinations. As part of prescription drug misuse monitoring, the physician performs a random urine drug screen that is positive for opioids and phencyclidine (PCP). The patient insists that he is not taking PCP. Which of the following medications could be causing a false-positive result on his urine drug screen?

Question

A 63-year-old man comes to the office for routine follow-up a month after being prescribed morphine for chronic, treatment-resistant back pain.  The patient says that his pain is greatly reduced since starting the morphine.  He has been able to begin a light exercise regimen for the first time in over 2 years.  His other medical conditions include hypertension, type 2 diabetes mellitus, allergic rhinitis, and major depressive disorder.  Temperature is 36.1 C (97 F), blood pressure is 118/84 mm Hg, pulse is 62/min, and respirations are 12/min.  The patient has normal range of motion of the spine, and movement is associated with a reduction in pain compared with previous examinations.  As part of prescription drug misuse monitoring, the physician performs a random urine drug screen that is positive for opioids and phencyclidine (PCP).  The patient insists that he is not taking PCP.  Which of the following medications could be causing a false-positive result on his urine drug screen?

Quizplus · Accepted Answer

11ec25c8_d7f1_12f0_bc81_4df47d8a95b3_MD0003_00 Standard urine drug screens (UDS) typically test for amphetamines, cocaine, cannabis, opioids, and phencyclidine; they are usually performed by immunoassay, which can yield false-positive results when specific cross-reacting medications or drugs are present. Among the medications listed, the commonly used over-the-counter cough suppressant dextromethorphan may cause a false-positive result for phencyclidine (PCP). Other commonly used medications that can cause a false-positive PCP result include diphenhydramine, doxylamine, ketamine, tramadol, and venlafaxine. Any positive result on an initial screening test can be verified using another assay. Gas chromatography/mass spectrometry is a highly sensitive and specific technique that can be used to check the accuracy of standard UDS results. Most standard UDS detect opioids by testing for morphine, a metabolite of natural opioids (eg, heroin, codeine); this patient tested positive for opioids, as expected. In contrast, semi-synthetic (eg, hydrocodone, hydromorphone, oxycodone) and synthetic (eg, fentanyl, meperidine, methadone, tramadol) opioids typically do not trigger positive UDS. (Choices A, B, D, and E) Bupropion, phenylephrine, and the beta blockers atenolol and propranolol may cause a false-positive amphetamine test result, but not a false-positive PCP result. Educational objective: The most frequently used standard urine drug screens (UDS) test for amphetamine, cocaine, cannabis, opioids, and phencyclidine. Dextromethorphan may cause a false-positive phencyclidine result. Most UDS detect natural opioids (eg, morphine, heroin, codeine) but not semi-synthetic or synthetic opioids. References: Clinical interpretation of urine drug tests: what clinicians need to know about urine drug screens. (http://www.ncbi.nlm.nih.gov/pubmed/28325505) Utility of point-of-care urine drug tests in the treatment of primary care patients with drug use disorders. (http://www.ncbi.nlm.nih.gov/pubmed/27159345)

A 63-Year-Old Man Comes to the Office for Routine Follow-Up