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can amoxicillan cause a false positive for cocain?

can amoxicillan cause a false positive for cocain on a urine test?
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First Helper Bidgette

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replied November 2nd, 2011
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It is commonly stated in the lay literature that if you take amoxicillin, you can show positive for cocaine. This is because the penicillin antibiotics and cocaine share a metabolite, benzoylecgonine. But, the amount produced by the anitbiotics is very, very small, compared to that produced by the metabolism of cocaine.

So, depending upon the testing, it may be possible to show the metabolite. But, in most tests the amount from amoxicillin is not high enough to register on the test as positive.

If, however, the initial testing of the sample does come up positive, further analysis of the sample by GC/MS (gas chromtograph/mass spectometry) will be able to tell where the metabolite came from.

The following is an abstract which looked at whether or not amoxicillin can cause a positive test.

J Anal Toxicol. 2008 May;32(4):315-8.

Failure of Amoxicillin to Produce False-Positive Urine Screens for Cocaine Metabolite.

Reisfield GM, Haddad J, Wilson GR, Johannsen LM, Voorhees KL, Chronister CW, Goldberger BA, Peele JD, Bertholf RL.

Source: Department of Community Health and Family Medicine, University of Florida Health Science Center, Jacksonville, Florida, USA.


Amoxicillin has been causally linked in the lay and medical literature to false-positive urine drug screens for cocaine metabolites. An exhaustive search of the peer-reviewed medical literature revealed no data to support this link. We hypothesized that amoxicillin does not cause false-positive urine drug screens for cocaine metabolites. To test this hypothesis, we examined the urine of 33 subjects administered a course of amoxicillin, subjecting the specimens to four common urine screening immunoassays. Thirty-one specimens were negative for the cocaine metabolite, benzoylecgonine (BE), by all four screening methods; two were positive for BE by all four screening methods. Both positive specimens were confirmed by gas chromatography-mass spectrometry (GC-MS) for the presence of BE at > 150 ng/mL. Three specimens that screened negative, but produced absorbance values that were intermediate between negative and positive controls, were submitted for GC-MS analysis; BE was detected in all three specimens at concentrations of 54, 94, and 119 ng/mL. Twenty-eight specimens produced screening results indistinguishable from negative controls.

Within the limitations of the study design, we conclude that amoxicillin is unlikely to produce false-positive urine screens for cocaine metabolites.

Though this study says it is unlikely, the authors do state that in two of their samples, the metabolite was found, and at high enough levels to be considered positive.

So, you will have to make what you want from the abstract. You can probably get access to the whole article if you wish.

Good luck.
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