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Tuesday, September 2, 2014
Pharmacy and Medications
Urine drug testing
I recently was on Flexeril and Vicodin after a fall and briusing my ribs and breaking my foot. My urine drug screen came back positive for benzodiazapines. How can that be? The only other drugs I was on was my routine drugs Wellbutrin XL, Avalide, Nexium and Ortho-prefest.
A positive drug screen for benzodiazepines on a urine drug screen (UDS) in the absence of a legitimately prescription is often considered evidence of drug abuse. Your question refers to the possibility that a legitimately prescribed medication might cause a false positive for another medicine on a UDS.
Other names for the drugs you take are as follows: Flexeril® cyclobenzaprine, Vicodin® a combination of acetaminophen (paracetamol) and hydrocodone Wellbutrin XL ® - sustained release bupropion typically used for depression, Avalide® hydrochlorothiazide/irbesartan for blood pressure, Nexium® - esomeprazole for gastric reflux and peptic ulcer disease, and Ortho - Prefest® hormone replacement therapy that consists of tablets containing estradiol and a combination of estradiol and norgestimate.
There are a number of UDS products available on the market. The various products can differ somewhat in their ability to produce or prevent false positive results. For example, a common OTC cough suppressant, dextromethorphan, can cause a false positive for Phencyclidine (PCP). We have information on the cross reactivities for some of the available UDS products. We reviewed this information and found that none of the medicines you take produce false positives for benzodiazepines on these screens. In fact, the benzodiazepine screens for which we have information appear to have minimal risk for false positives. It is interesting that one of the cross-sensitivity lists indicated that the test developer had checked their benzodiazepine screen for false positives with cyclobenzaprine. This could mean that some benzodiazepine UDS products have trouble with this medicine. The medical review officer for the company or agency that required the UDS should have information about the cross-reactivities for the specific UDS they are using.
In order for UDS results to be used for most legal purposes, any positive result must be confirmed by a more specific method, typically gas chromatography mass spectrophotometry (GCMS). Without confirmation, it can be difficult or impossible to separate true positives from false positive results and an innocent individual might be accused or punished unjustly. If you think the UDS you took has produced a false positive result, ask if they did a confirmatory test, and discuss your result with the medical review officer. If you suffer some undue consequence as a result of a false positive drug screen, you could have legal justification to seek damages for that undue consequence.
Robert James Goetz, PharmD, DABAT
Assistant Professor of Pharmacy Practice
College of Medicine
University of Cincinnati