Laboratory Monitoring of OxyContin (Oxycodone): Clinical Pitfalls

Abstract

Some patients have headaches that are refractory to standard treatments, and they require chronic administration of opioid analgesics. The use of opioids in a clinical setting must be closely monitored due to the medications' potential for addiction, abuse, and fatal interactions. Limited access to opioids and the demand for them outside the clinical setting leads to another danger. Patients can mislead their providers into prescribing opioids, intending to sell the medications instead of using them to alleviate their own pain. For protection of the patient, as well as the community, it is vital that such activity be prevented. We recently encountered a patient we suspected of abusing or misusing OxyContin (oxycodone). In order to determine whether the patient was taking the medication as prescribed, we ordered a urine-based immunoassay drug screen. The results were negative; the patient appeared to not have oxycodone in his system. Based on these results, we dismissed the patient from our practice. At the patient's request, a second test was performed, this time using gas chromatography-mass spectrometry. It indicated that the patient did indeed have sufficiently high levels of oxycodone in the urine. The minimum level threshold was too high to detect the presence of oxycodone in the immunoassay. We would like to help prevent future misunderstandings such as we experienced. To do so, we will first present the case of our patient, followed by a discussion of the actions taken. Finally, we will provide an overview of analgesic monitoring systems.

Drugs of Abuse Testing

“…This value confirmed that the patient was compliant with his oxycodone usage [10]. Although his pain was under control, he routinely called the clinic stating that he had finished his medication faster and needed a refill.…”

Challenges in Drugs of Abuse Testing

“…Unfortunately, due to the low crossreactivity of oxycodone with the opiate immunoassay originally used by the laboratory for screening his urine specimen, the minimum threshold for positive was 2000 ng/mL of oxycodone (26) . After several years of using shortacting opioid analgesics, the clinician determined that oxycodone 20 mg dosage twice a day was needed for his headache management.…”

Comparison of Response of DRI Oxycodone Semiquantitative Immunoassay With True Oxycodone Values Determined by Liquid Chromatography Combined With Tandem Mass Spectrometry: Sensitivity of the DRI Assay at 100 ng/ml Cut‐Off and Validity of Semiquantitative Value

“…An aliquot of the original urine specimen was retested using gas chromatography combined with mass spectrometry (GC/MS) in a reference laboratory and the presence of oxycodone at 1,124 ng/ml was confirmed indicating that the patient was compliant with the oxycodone prescription. The original negative result using opiate immunoassay was determined to be due to poor crossreactivity of oxycodone with the opiate immunoassay . Therefore, proper testing and selection of the appropriate assay is essential in monitoring therapy in pain management patients.…”