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Date of last update: 9/5/2017.

Forum Name: Pharmacy & Drug Topics

Question: antibiotic cause false positive methamphetamineon drug test

 swoll - Sun Jan 25, 2009 7:33 pm

hi i was wondering if you have any refs or information that has to do with antibiotics (such as pencillin doxycyline bactrim etc.. was on all + more) causing a false positive amphetamine or methamphetamine urine test?
i have not taken any amphetamine, or similar substances i think, but i was in for surgery for an infection and now i have shown up (the next day after surgery) positive on a urine test at the methadone clinic. i have been there 10 years without failing a drug test and now i have to go in daily instead of bi-weekly! 4+ hr round trip really is hard daily. any help will be greatly appreciated! - jason r.
 Debra Van Ness RN - Mon Feb 23, 2009 12:09 pm

I would want to ask if you have taken any other prescribed medications or over the counter products. Some medications such as those in cold remedies/sinus medications over the counter can cause a false positive amphetamine screen. Pseudoephedrine is a big one. (Sudafed's original formula). Ephedra will also do this. (although I am not sure Ephedra is even accessable now over the counter anywhere). However, I believe that the exact culprit can be identified through specific blood tests. What may show up as a postive amphetamine on a urine screen can be confirmed on a blood test. Blood work will even differentiate between an amphetamine and a methamphetamine.
So, though it may cost money and be more of an effort, you could request a serum drug screen in order to prove yourself.

Please be sure to give a list of everything you take prescribed and non prescribed before your drug screens. Include all herbal substances and over the counter supplements.

Debra Van Ness RN
 ToxPro - Thu May 28, 2009 5:24 pm

Antibiotics are not known to cross-react with modern drugs of abuse screening kits for amphetamines. That said, a urine drugs of abuse screen should always be confirmed, typcially by Gas Chromatography/Mass Spectrometry (GCMS). The are too many other-the-counter compounds (decongestants, diet pills) that can cause a false positive for amphetamines. This method of confirmation will also differentiate methamphetamine from amphetamine or phentermine, two commonly prescribed sympathomimetic amines that yield positive screening tests.

While a blood test may be helpful, it is not necessarily needed - the original urine should be confirmed by (at least) GCMS.

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