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Published:
Journal of Analytical Toxicology,
ISSN 0146-4760,
Volume 30, Number 8, October 2006,
pp.570-575
Incomplete Recovery of Prescription Opioids in Urine using
Enzymatic Hydrolysis of Glucuronide Metabolites
Ping Wang[1,2], Judith A. Stone[1,2], Katherine H. Chen[1,2],
Susan F. Gross[1,2], Christine A. Haller[1,2,3], and Alan H.B. Wu[1,2],
[1]Clinical Laboratories, San Francisco General Hospital, San Francisco, California
and
Departments of
[2]Laboratory Medicine and
[3]Medicine, University of California at San Francisco, San Francisco, California
Confirmation of opioids in urine samples of clinical patients
requires liberation of opioids from their glucuronide conjugates. Both acid
hydrolysis and enzyme hydrolysis using b-glucuronidase from various sources
have been reported, with the latter approach prevailing in most clinical toxicology
laboratories. The goal of this study was to compare the efficiency of acid versus
different enzyme hydrolysis methods in recovering morphine and common semisynthetic
opioids from glucuronide standards and 78 patient urine samples that were screened
positive for opioids as a class. Specimens were analyzed with a validated gas
chromatography–mass spectrometry (GC–MS) procedure. With the exception
of oxycodone, the results indicated that the majority of opioids tested were
extensively glucuronide-conjugated in urine. Significantly, acid hydrolysis
liberated > 90% of morphine and hydromorphone from their glucuronide standards
but enzyme hydrolysis had lower and variable efficiency, depending on the opiate
type and the enzyme source. In patient specimens, much higher concentrations
of free codeine, morphine, hydromorphone, and oxymorphone were obtained with
acid hydrolysis than with various enzyme methods. Incomplete hydrolysis using
b-glucuronidase could lead to false-negative results for many opioids when urine
is tested for drugs of abuse. We conclude that acid hydrolysis is the method
of choice for GC–MS confirmation of urine opioids.
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