In this episode, I’ll discuss potential reasons for an unexpected positive urine barbiturate screen.
When a urine drug screen comes up positive for barbiturates unexpectedly, healthcare practitioners often suspect the result is a false positive. Both ibuprofen and naproxen have been reported to cause a false positive urine barbiturate result in a study of healthy volunteers. This study found that 2 of 102 patients taking NSAIDs had a false-positive for barbiturates by the fluorescence polarization immunoassay (FPIA). One patient was taking ibuprofen and one was taking naproxen.
In my practice, I have found that it is far more common for a patient with an unexpected positive urine barbiturate screen to actually be taking a barbiturate. The barbiturate that often flies under the radar of clinicians is butalbital. This short-acting barbiturate is a component of Fioricet or Esgic, a commonly prescribed analgesic. However because butalbital is not used for any other indication or available separately, many clinicians do not realize that it is in fact a barbiturate.
Whenever I am asked to investigate an unexpected urine barbiturate screen, the first thing I do is look for butalbital in the patient’s home medication list or medication administration record. More often than not, butalbital use explains the positive screen. Also, if I recommend a urine drug screen for a patient I first check to see if they have been taking butalbital. If so, I make sure to let the patient’s nurse and physician know to expect the barbiturate screen to be positive.
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If you like this post, check out my book – A Pharmacist’s Guide to Inpatient Medical Emergencies: How to respond to code blue, rapid response calls, and other medical emergencies.