Mexiletine and False Positive Urine Drug Screen for Amphetamine: A Case Review

Abstract

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.

False Positive Tramadol Urine Testing in Patients Taking Fexofenadine: A Tale of Two Consecutive Cases

“…Reports of false negative urine screening results in the context of SUD have been circulating in the literature throughout the last two decades ([ 10 ]). Reports of such diagnostic inaccuracy kept trickling until recently with strong detrimental effect on therapeutic alliance and doctor-patient trust ([ 11 ]). Agreement between self-reported use and urine-confirmed drug use results was lowest for opioids ([ 12 ]), hence compromising an indispensable reliance on urine testing for detection of such substances.…”

Guilty or not guilty? — False positive results of common medicines in drug tests: review and practical guide

“…Mexiletine: A 64-year-old patient prescribed mexiletine medication tested positive for amphetamines twice during urine toxicology screens while hospitalized, despite denying drug use. Additional confirmatory testing yielded negative results, suggesting false positives likely caused by cross-reactivity or other factors [44]. Similarly, two patients on mexiletine treatment tested positive for amphetamines on all screens but showed negative results upon mass spectrometry confirmation, indicating false positives.…”