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Mechanism of false-negative urine
cannabinoid immunoassay screens by Visine eyedrops.
Pearson SD, Ash KO, Urry FM
Department of Pathology, University of Utah School of
Medicine, Salt Lake City 84132.
To drug-free urine specimens, we added the following
drugs of abuse to give concentrations twice the cutoff
value for positive test results:
11-nor-9-carboxy-delta-9-tetrahydrocannabinol
(9-carboxy-THC), oxazepam, secobarbital, morphine,
benzoylecgonine, amphetamine, or phencyclidine (PCP).
Visine was then added. Although measured concentrations
of several drugs were decreased in the presence of
Visine, false-negative results were obtained only for
9-carboxy-THC for the EMIT-d.a.u. and TDx urine
cannabinoid assays. Visine also decreased 9-carboxy-THC
as measured by the Abuscreen assay. At low
concentrations of Visine, false-negative cannabinoid
results were attributable to the benzalkonium chloride
ingredient of Visine. The added Visine was not
detectable by routine urine analysis and had no effect
on the activity of the glucose-6-phosphate dehydrogenase-drug
conjugate used in the EMIT-d.a.u. assays. Moreover,
analysis by gas chromatography/mass spectrometry showed
no chemical modification or loss of 9-carboxy-THC in the
Visine-adulterated urine specimens. However, Visine did
increase the adhesion of 9-carboxy-THC to the
borosilicate glass specimen containers. Results of
ultrafiltration studies with Visine suggest that
9-carboxy-THC partitions between the aqueous solvent and
the hydrophobic interior of benzalkonium chloride
micelles, thereby reducing the availability of
9-carboxy-THC in antibody-based assays.
PMID: 2467764, UI: 89195644
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