SOFT 2004 Meeting Abstracts - Society of Forensic Toxicologists

C13
A HOMOGENEOUS ENZYME IMMUNOASSAY FOR THE DETECTION OF
OXYCODONE AND OXYMORPHONE IN URINE
Lakshmi Anne* Ming-che Wang, Vani Bodepudi, Scott Casseday, Manolito Datuin and Daryush
Mirlohi; Microgenics Corporation, 46360 Fremont Boulevard, Fremont, CA.
Oxycodone is an opioid analgesic derived from thebaine. It is structurally similar to codeine with a higher
abuse potential than morphine. Oxycodone is prescribed for the treatment of moderate to severe pain,
chronic pain or terminal cancer pain and is available as OxyContin® or in combination with acetaminophen
or aspirin. Oxycodone is metabolized to oxymorphone, an active metabolite that has the same analgesic
potency as oxycodone. Other metabolites of oxycodone include noroxycodone and noroxymorphone, which
are inactive. The majority of oxycodone is excreted in urine within 24 hours as free oxycodone, conjugated
oxycodone and oxymorphone. Increased use of oxycodone has resulted in an increase in oxycodone abuse
and abuse-related deaths. None of the currently available opiate immunoassays has the sensitivity to detect
oxycodone or oxymorphone at therapeutic or abuse levels. The objective of this study is to develop a
homogeneous immunoassay for the specific detection of oxycodone and oxymorphone at therapeutic as
well as abuse levels in urine.
Microgenics DRI® Oxycodone Assay is a dual cutoff assay using 100 nglmL and 300 ng/mL oxycodone as
cutoff calibrators. The assay uses a highly specific monoclonal antibody that can detect both oxycodone
and oxymorphone. The assay is based on competition between drug labeled with glucose-6-phosphate
dehydrogenase (G6PDH) and free drug from urine sample for a fixed amount of antibody binding sites. In
the absence of free drug from the sample, the specific antibody binds the enzyme labeled drug causing a
decrease in enzyme activity. This phenomenon creates a direct relationship between the drug concentration
in urine and enzyme activity. The enzyme activity is determined spectrophotometrically at 340 nm by
measuring its ability to convert NAD to NADH.
The reagents and calibrators are liquid ready-to-use. The dynamic range of the assay is 0 to 1000 ng/mL.
The performance ofthe assay was evaluated on the Hitachi 717 analyzer. The within-run and total precision
(CV) for the cutoff calibrators and ± 25% controls is