False-positive phencyclidine (PCP) on urine drug screen attributed to desvenlafaxine (Pristiq) use

Advanced heart failure patients commonly suffer from ventricular arrhythmias which can be managed by antiarrhythmic drugs like mexiletine. These ventricular arrhythmias can be complicated by illicit drug use which alter outcomes and can potentially impact the patient-physician relationship through countertransference. However, mexiletine can lead to false positive urine drug screen testing for amphetamine, and these false-positive urine drug screen test results can affect the decision-making process. Health care providers should be aware of this fact and should either use confirmatory testing or look for confounding compounds in patients who deny using illicit substances and have a positive urine drug screen. Our patient is 64 years old who arrived at the emergency department after experiencing a shock by his intracardiac defibrillator. The patient tested positive for amphetamine on his urine drug screen and was later ruled out by confirmatory quantitative testing.

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Can tapentadol cause a false-positive urine drug screen result for amphetamine?

Clinical Toxicology ◽

10.3109/15563650.2012.735367 ◽

2012 ◽

Vol 50 (10) ◽

pp. 1174-1175 ◽

Cited By ~ 1

Author(s):

Schirin Tang ◽

Michael E. Mullins ◽

Benjamin M. Braun ◽

Karl G. Hock ◽

Mitchell G. Scott ◽

...

Keyword(s):

False Positive ◽

Drug Screen ◽

Urine Drug Screen ◽

Screen Result ◽

Positive Urine ◽

Urine Drug

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Reduced Interference by Phenothiazines in Amphetamine Drug of Abuse Immunoassays

Archives of Pathology & Laboratory Medicine ◽

10.5858/2006-130-1834-ribpia ◽

2006 ◽

Vol 130 (12) ◽

pp. 1834-1838

Author(s):

Stacy E. F. Melanson ◽

Elizabeth Lee-Lewandrowski ◽

David A. Griggs ◽

William H. Long ◽

James G. Flood

Keyword(s):

Emergency Department ◽

False Positive ◽

Massachusetts General Hospital ◽

Parent Compound ◽

Drug Screen ◽

Urine Drug Screen ◽

Drug Of Abuse ◽

Positive Urine ◽

Urine Drug ◽

Positive Results

Abstract Context.—Emergency department physicians frequently request urine drug screens, but many are unaware of their limitations, including the potential for false-positive results. Promethazine, a phenothiazine derivative, is used for the treatment of allergies, agitation, nausea, and vomiting. Many patients taking promethazine are subject to urine drug screens and any potential interferences are important to recognize. Design.—During an 11-month period, all patients presenting to the Massachusetts General Hospital emergency department who had a finding of promethazine in their serum drug screen, and who also had a urine drug screen performed, were selected for inclusion in the study. The urine drug screen results (n = 22 patients/samples) were then studied. Objective.—To determine if promethazine use can cause false-positive urine amphetamine results in widely used drug of abuse immunoassays. Results.—Thirty-six percent of patients taking promethazine had false-positive test results for urine amphetamines using the EMIT II Plus Monoclonal Amphetamine/Methamphetamine Immunoassay. Sixty-four percent of patients showed cross-reactivity greater than 20% higher than the blank calibrator rate. In a separate, related study, no promethazine-induced false-positive results were seen with the EMIT II Plus, Triage, and TesTcard 9 amphetamine assays, or the Triage methamphetamine assay. Reduced chlorpromazine interference was also seen with these other assays. Conclusions.—False-positive urine amphetamine results can be obtained in patients taking promethazine. Promethazine metabolite(s), and not the parent compound, are the likely cause of these urine false-positive results obtained with EMIT II Plus Monoclonal Amphetamine/Methamphetamine Immunoassay. Immunoassays from different manufacturers can have very different “interference” profiles, which the pathologist and laboratory scientist must understand and relay to clinicians.

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