Stability of pain-related medications, metabolites, and illicit substances in urine Elizabeth Gonzales a, ⁎, Gary Ng b , Amadeo Pesce a , Cameron West a , Robert West a , Charles Mikel a , Sergey Latyshev a , Perla Almazan a a Millennium Research Institute, 16980 Via Tazon, San Diego, CA 92127, USA b Millennium Laboratories, 16981 Via Tazon, San Diego, CA 92127, USA abstract article info Article history: Received 6 April 2012 Received in revised form 17 November 2012 Accepted 19 November 2012 Available online 29 November 2012 Keywords: Urine drug testing Stability Opioids LC-MS/MS Illicit substances Pain Background: Effective urine drug testing requires an understanding of the stability of medications, metabolites and other substances excreted in the urine matrix. When the testing results do not fit the clinical picture, physi- cians frequently request repeat testing of the original specimen in order to corroborate the results. We deter- mined the stability in urine of various medications, metabolites, and illicit substances commonly requested for testing by physicians treating patients with pain and pain-related disorders. Methods: Quantitative analyses of urine specimens were performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Two replicates at a high and low concentration were analyzed at time 0, and after 2, 3 and 6 months following storage at +4 °C and -20 °C. At each time interval, the percent difference from time 0 for each analyte was calculated and averaged for each storage condition. Results: For the majority of medications, the percent differences were within 20% of the original measurement for all 3 storage conditions. All were within 30% of the original measurement after 2, 3 and 6 months in all stor- age conditions, except for 7-amino-clonazepam, and carboxy-tetrahydrocannabinol. Conclusions: The findings from the current study confirm that the majority of medications, metabolites, and illicit substances commonly requested for testing by physicians treating patients with pain and pain-related disorders are stable within 20% of the original concentration when stored refrigerated or frozen for up to 6 months. Thus, delayed testing, repeat testing, and add-on testing of urine specimens can yield reliable results for up to 6 months following the urine collection date. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Physicians treating patients with chronic pain and pain-related disor- ders often utilize urine drug testing as part of their comprehensive treat- ment and monitoring plan [1,2]. Urine drug testing is commonly carried out at reference laboratories, requiring that specimens be transported to the testing facility. The time between collection and analysis can be sever- al days. Because of this time interval, to assure that results are accurate, it is necessary to demonstrate that specimens are stable during this time frame. In addition, situations may arise when the time between collection and analysis is more than several days. These situations include repeat testing for analytical purposes, repeat testing when the test results do not fit the clinical picture, repeat testing to add additional drugs to the test panel, and repeat testing when a specimen produces an unexpected result [3,4]. In the event that the analyte in question is not stable in the urine specimen, degradation can occur in the time between the initial test and the re-test. In these instances, the results of the re-test may vary from the original test result. Previous studies have been conducted to determine the stability of select drugs in urine under different storage temperatures. However, there has not been a comprehensive study conducted to determine the stability of medications, metabolites, and illicit substances commonly re- quested for testing by physicians treating patients with pain and pain-related disorders. See Table 1 for a summary of the extant literature [5–12]. The majority of the published studies on drug stability in urine have addressed mostly illicit substances such as heroin, methamphetamine, THC, and cocaine, and only few select opioid medications, such as morphine and codeine. These studies have shown that specimens frozen at -20 °C and those stored at +4 °C are stable over a period of months [5–9,11]. Most often, specimens sent to reference laboratories are stored at + 4 °C because freezing and then thawing large numbers of urine spec- imens is impractical. However, those specimens that need to be set aside for legal purposes may be stored frozen. There is a dearth of information on the stability in urine over time of the types of medications requested for testing by physicians treating patients with pain and pain-related disorders. Clinica Chimica Acta 416 (2013) 80–85 ⁎ Corresponding author. Tel.: +1 888 756 1627; fax: +1 858 217 1756. E-mail address: egonzales@millenniumlabs.com (E. Gonzales). 0009-8981/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cca.2012.11.020 Contents lists available at SciVerse ScienceDirect Clinica Chimica Acta journal homepage: www.elsevier.com/locate/clinchim