Quantitative Analysis of Buprenorphine, Norbuprenorphine, and Their Glucuronide Metabolites in Human Urine

We present a quantitative clinical LC-MS/MS assay for the simultaneous analysis of buprenorphine, norbuprenorphine, and their glucuronide metabolites in human urine. The assay is based on the direct and hydrolysis-free sample preparation protocol, i.e., dilute and shoot, whereby clarified urine specimens are diluted in internal standard reagent and injected into the LC-MS/MS instrument. The analytical platform employs reversed-phase liquid chromatography for upfront separation and electrospray ionization multiple reaction monitoring MS detection via the triple-quadrupole (TSQ Quantiva) instrument. The assay has a quantitative analytical range of 5 ng/mL-1000 ng/mL represented at seven levels for each of the four analytes. A unique stable isotopically labeled analogue is used as internal standard for each analyte. For high-throughput performance, the assay can be multiplexed between two LC channels.

Buprenorphine, Norbuprenorphine, and Naloxone Levels in Adulterated Urine Samples: Can They be Detected When Buprenorphine/Naloxone Film is Dipped into Urine or Water?

Reportedly, various urine manipulations can be performed by opioid use disorder (OUD) patients who are on buprenorphine/naloxone medications to disguise their non-compliance to the treatment. One type of manipulation is known as "spiking" adulteration, directly dipping a buprenorphine/naloxone film into urine. Identifying this type of urine manipulation has been the aim of many previous studies. These studies have revealed urine adulterations through inappropriately high levels of "buprenorphine" and "naloxone" and a very small amount of "norbuprenorphine." So, does the small amount of "norbuprenorphine" in the adulterated urine samples result from dipped buprenorphine/naloxone film, or is it a residual metabolite of buprenorphine in the patient's system? This pilot study utilized 12 urine samples from 12 participants, as well as water samples as a control. The samples were subdivided by the dipping area and time, as well as the temperature and concentration of urine samples, and each sublingual generic buprenorphine/naloxone film was dipped directly into the samples. Then, the levels of "buprenorphine," "norbuprenorphine," "naloxone," "buprenorphine-glucuronide" and "norbuprenorphine-glucuronide" were examined by Liquid Chromatography with tandem mass spectrometry (LC-MS/MS). The results of this study showed that high levels of "buprenorphine" and "naloxone" and a small amount of "norbuprenorphine" were detected in both urine and water samples when the buprenorphine/naloxone film was dipped directly into these samples. However, no "buprenorphine-glucuronide" or "norbuprenorphine-glucuronide" were detected in any of the samples. In addition, the area and timing of dipping altered "buprenorphine" and "naloxone" levels, but concentration and temperature did not. This study's findings could help providers interpret their patients' urine drug test results more accurately, which then allows them to monitor patient compliance and help them identify manipulation by examining patient urine test results.

Investigation of Simulated Adherence in Long-Term Buprenorphine/Naloxone Treatment Patients

BACKGROUND

Buprenorphine is a medication that is used to treat opioid use disorder by reducing withdrawal symptoms and cravings for opioids. Patients with poor adherence are at higher risk of relapse and overdose. Providers often test adherence through urine testing but are not aware of simulated adherence, where patients may directly add buprenorphine to the urine samples. As of now, there exists no literature on the simulated adherence practices for patients who stayed in the treatment for more than three months.

METHODS

This study is a cross-sectional analysis of simulated adherence through urine toxicology results of 3950 patients undergoing buprenorphine/naloxone treatment. Simulated adherence was measured by the ratio of norbuprenorphine and buprenorphine <0.02 in the urine sample. Descriptive statistics as well as multivariate analysis was conducted to examine the relationship between patient information and outcomes.

RESULTS

Out of 3950 patients, 411 (10.4%) had a history of one or more simulated adherence. On average, patients with multiple simulated adherences had 48.1% of their tests simulated, while on the contrary, patients with a single occurrence of simulated adherence had 17.6% of their tests simulated. Weekly testing and visit number of over 15 were associated with a higher likelihood of simulated adherence.

CONCLUSION

The study demonstrates that simulated adherence is a recurring phenomenon among buprenorphine/naloxone treatment patients regardless of the duration in the treatment. Utilization of quantitative urine toxicology to identify simulated adherence will enable healthcare providers to formulate a more precise and effective treatment plan tailored to support individual patient needs.

Evaluation of adherence monitoring in buprenorphine treatment: A pilot study using timed drug assays to determine accuracy of testing

AIMS

Buprenorphine is effective at reducing relapse to opioid misuse, morbidity and mortality in opioid-dependent patients. Urine drug screening (UDS) to assess adherence is used routinely in opioid agonist treatment (OAT). The primary aim of this study was to determine factors which may be associated with a negative qualitative urine drug screen for buprenorphine in OAT patients.

METHODS

This prospective pilot study was conducted at a tertiary addiction medicine centre. Twenty participants on stable treatment underwent supervised administration of sublingual buprenorphine. Matched urine and blood samples were collected prior to and 2, 4 and 6 hours after buprenorphine administration. Qualitative urine drug screen results were obtained using gas chromatography-mass spectrometry (GC-MS), while quantitative blood and urine results were obtained using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS).

RESULTS

Qualitative urine assay yielded a negative result for buprenorphine in 57% of tested samples. The median concentration of urinary buprenorphine was 167 mcg/L (range: 2-1730 mcg/L). Thirty percent of all blood samples did not detect buprenorphine (range 0-18 mcg/L). Positive qualitative urine drug screen results were associated with higher urine (343 mcg/L compared with 75 mcg/L; P < .05) and blood (4 mcg/L compared with 2 mcg/L; P < .05) buprenorphine concentrations. Median urine concentrations of buprenorphine were highest at 2 hours and were higher in participants receiving CYP3A4 inhibitors.

CONCLUSION

Interpretation of qualitative urine drug screens to assess adherence in OAT is complex. Poor adherence with treatment cannot be assumed in patients returning a negative qualitative GC-MS urine drug screen.

Association of Patients' Direct Addition of Buprenorphine to Urine Drug Test Specimens With Clinical Factors in Opioid Use Disorder

Importance

The direct addition of buprenorphine to urine drug test specimens to mimic results suggestive of adherence is a clinically significant result, yet little is known about the phenomenon.

Objective

To characterize factors associated with the direct addition of buprenorphine to urine specimens among patients prescribed buprenorphine for opioid use disorder.

Design, Setting, and Participants

This cross-sectional study of urine drug test specimens was conducted from January 1, 2017, to April 30, 2022, using a national database of urine drug test specimens ordered by clinicians from primary care, behavioral health, and substance use disorder treatment clinics. Urine specimens with quantitative norbuprenorphine and buprenorphine concentrations from patients with opioid use disorder currently prescribed buprenorphine were analyzed.

Exposures

Nonprescribed opioid or stimulant co-positive, clinical setting, collection year, census division, patient age, patient sex, and payor.

Main Outcomes and Measures

Norbuprenorphine to buprenorphine ratio less than 0.02 identified direct addition of buprenorphine. Unadjusted trends in co-positivity for stimulants and opioids were compared between specimens consistent with the direct addition of buprenorphine. Factors associated with the direct addition of buprenorphine were examined with generalized estimating equations.

Results

This study included 507 735 urine specimens from 58 476 patients. Of all specimens, 261 210 (51.4%) were obtained from male individuals, and 137 254 (37.7%) were from patients aged 25 to 34 years. Overall, 9546 (1.9%) specimens from 4550 (7.6%) patients were suggestive of the direct addition of buprenorphine. The annual prevalence decreased from 2.4% in 2017 to 1.2% in 2020. Opioid-positive with (adjusted odds ratio [aOR], 2.01; 95% CI, 1.85-2.18) and without (aOR, 2.02; 95% CI, 1.81-2.26) stimulant-positive specimens were associated with the direct addition of buprenorphine to specimens, while opioid-negative/stimulant-positive specimens were negatively associated (aOR, 0.78; 95% CI, 0.71-0.85). Specimens from patients aged 35 to 44 years (aOR, 1.59; 95% CI, 1.34-1.90) and primary care (aOR, 1.60; 95% CI, 1.44-1.79) were associated with the direct addition of buprenorphine. Differences by treatment setting decreased over time. Specimens from the South Atlantic census region had the highest association (aOR, 1.4; 95% CI, 1.25-1.56) and New England had the lowest association (aOR, 0.54; 95% CI, 0.46-0.65) with the direct addition of buprenorphine.

Conclusions and Relevance

In this cross-sectional study, the direct addition of buprenorphine to urine specimens was associated with other opioid positivity and being collected in primary care settings. The direct addition of buprenorphine to urine specimens is a clinically significant finding, and best practices specific for this phenomenon are needed.

Association Between Buprenorphine Dose and the Urine "Norbuprenorphine" to "Creatinine" Ratio: Revised

Background

Utilizing a 1-year chart review as the data, Furo et al. conducted a research study on an association between buprenorphine dose and the urine "norbuprenorphine" to "creatinine" ratio and found significant differences in the ratio among 8-, 12-, and 16-mg/day groups with an analysis of variance (ANOVA) test. This study expands the data for a 2-year chart review and is intended to delineate an association between buprenorphine dose and the urine "norbuprenorphine" to "creatinine" ratio with a higher statistical power.

Methods

This study performed a 2-year chart review of data for the patients living in a halfway house setting, where their drug administration was closely monitored. The patients were on buprenorphine prescribed at an outpatient clinic for opioid use disorder (OUD), and their buprenorphine prescription and dispensing information were confirmed by the New York Prescription Drug Monitoring Program (PDMP). Urine test results in the electronic health record (EHR) were reviewed, focusing on the "buprenorphine," "norbuprenorphine," and "creatinine" levels. The Kruskal-Wallis H and Mann-Whitney U tests were performed to examine an association between buprenorphine dose and the "norbuprenorphine" to "creatinine" ratio.

Results

This study included 371 urine samples from 61 consecutive patients and analyzed the data in a manner similar to that described in the study by Furo et al. This study had similar findings with the following exceptions: (1) a mean buprenorphine dose of 11.0 ± 3.8 mg/day with a range of 2 to 20 mg/day; (2) exclusion of 6 urine samples with "creatinine" level <20 mg/dL; (3) minimum "norbuprenorphine" to "creatinine" ratios in the 8-, 12-, and 16-mg/day groups of 0.44 × 10-4 (n = 68), 0.1 × 10-4 (n = 133), and 1.37 × 10-4 (n = 82), respectively; however, after removing the 2 lowest outliers, the minimum "norbuprenorphine" to "creatinine" ratio in the 12-mg/day group was 1.6 × 10-4, similar to the findings in the previous study; and (4) a significant association between buprenorphine dose and the urine "norbuprenorphine" to "creatinine" ratios from the Kruskal-Wallis test (P < .01). In addition, the median "norbuprenorphine" to "creatinine" ratio had a strong association with buprenorphine dose, and this association could be formulated as: [y = 2.266 ln(x) + 0.8211]. In other words, the median ratios in 8-, 12-, and 16-mg/day groups were 5.53 × 10-4, 6.45 × 10-4, and 7.10 × 10-4, respectively. Therefore, any of the following features should alert providers to further investigate patient treatment compliance: (1) inappropriate substance(s) in urine sample; (2) "creatinine" level <20 mg/dL; (3) "buprenorphine" to "norbuprenorphine" ratio >50:1; (4) buprenorphine dose >24 mg/day; or (5) "norbuprenorphine" to "creatinine" ratios <0.5 × 10-4 in patients who are on 8 mg/day or <1.5 × 10-4 in patients who are on 12 mg/day or more.

Conclusion

The results of the present study confirmed those of the previous study regarding an association between buprenorphine dose and the "norbuprenorphine" to "creatinine" ratio, using an expanded data set. Additionally, this study delineated a clearer relationship, focusing on the median "norbuprenorphine" to "creatinine" ratios in different buprenorphine dose groups. These results could help providers interpret urine test results more accurately and apply them to outpatient opioid treatment programs for optimal treatment outcomes.

Investigation of buprenorphine-related deaths using urinary metabolite concentrations

Quantitative analysis of postmortem urine, instead of blood, for buprenorphine and metabolites may provide additional evidence for the diagnosis of fatal buprenorphine poisoning. In this study, 247 autopsy urine samples, previously testing positive for buprenorphine or norbuprenorphine, were quantitatively reanalysed with a recently developed liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for unconjugated buprenorphine (BUP), norbuprenorphine (NBUP), naloxone (NAL), and their respective conjugated metabolites, buprenorphine glucuronide (BUPG), norbuprenorphine glucuronide (NBUPG), and naloxone glucuronide (NALG). The cases were divided, according to medical examiners' decision, to buprenorphine poisonings and other causes of death. The groups were compared for urinary concentrations and metabolite concentration ratios of the six analytes. All median concentrations were higher in the buprenorphine poisoning group. The median concentration of BUPG was significantly higher and the median metabolite ratios NBUP/BUP, NBUPG/BUPG, and NBUPtotal/BUPtotal were significantly lower in poisonings than in other causes of death. Naloxone-related concentrations and ratios were not significantly different between the groups.

Urinary Buprenorphine, Norbuprenorphine and Naloxone Concentrations and Ratios: Review and Potential Clinical Implications

OBJECTIVES

Treatment with medications for opioid use disorder such as buprenorphine improves patient morbidity and mortality as well as treatment adherence, an important component of patient care. Buprenorphine is combined with naloxone to reduce misuse; and, when taken sublingually, naloxone is poorly absorbed. Urine testing for buprenorphine is a common way to monitor adherence. Some patients who want to appear adherent may directly tamper with their urine by adding buprenorphine to their urine to allow for the detection without ingestion. Practitioners may rely upon the concentration of buprenorphine and the metabolite, norbuprenorphine, and utilize the ratio of metabolite to parent compound (norbuprenorphine:buprenorphine - N:B ratio) to discern possible evidence of tampering; however, there remains debate as to what specific ratio may signify this practice. Testing for naloxone may also help determine if urine tampering occurred as only low naloxone concentrations are found in the urine when taken by a sublingual route.

METHODS

To determine a reliable N:B ratio that may be used to identify possible urine tampering by adding parent drug directly to urine, we examined 136,605 urine samples for quantitative concentrations of buprenorphine and norbuprenorphine by LC-MS/MS performed at a commercial laboratory. After identifying abnormal ratios (<0.02), we then compared them with naloxone concentrations and specimen validity testing, other markers that may coincide with specimen tampering of this type.

RESULTS

Correlating urinary buprenorphine and norbuprenorphine concentrations, we found 2 distinct patient populations, which could be distinguished by N:B ratios ranging from 0.01 to 0.2. In addition, while the distribution of urine naloxone concentrations itself did not demonstrate distinct populations, naloxone was able to further flag potential tampered specimens when combined with N:B ratios. Abnormal specimen validity testing was additionally found more commonly in cases with N:B ratios <0.02.

CONCLUSIONS

This comprehensive study compared N:B ratios with naloxone concentrations and specimen validity testing. This study suggests that a N:B ratio of <0.02 in concert with high naloxone concentrations (>1000 ng/ml) can help to identify potential cases of tampered urine samples.

Determination of buprenorphine, norbuprenorphine, naloxone, and their glucuronides in urine by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometry method for the simultaneous quantification of buprenorphine (BUP), norbuprenorphine (NBUP), naloxone (NAL), and their glucuronide conjugates BUP-G, NBUP-G, and NAL-G in urine samples was developed. The method, omitting a hydrolysis step, involved non-polar solid-phase extraction, liquid chromatography on a C18 column, electrospray positive ionization, and mass analysis by multiple reaction monitoring. Quantification was based on the corresponding deuterium-labelled internal standards for each of the six analytes. The limit of quantification was 0.5 μg/L for BUP and NAL, 1 μg/L for NAL-G, and 3 μg/L for NBUP, BUP-G, and NBUP-G. Using the developed method, 72 urine samples from buprenorphine-dependent patients were analysed to cover the concentration ranges encountered in a clinical setting. The median (maximum) concentration was 4.2 μg/L (102 μg/L) for BUP, 74.7 μg/L (580 μg/L) for NBUP, 0.9 μg/L (85.5 μg/L) for NAL, 159.5 μg/L (1370 μg/L) for BUP-G, 307.5 μg/L (1970 μg/L) for NBUP-G, and 79.6 μg/L (2310 μg/L) for NAL-G.

Use of urinary naloxone levels in a single provider practice: a case study

BACKGROUND

Urine drug monitoring for medications for opioid use disorder (MOUD) such as buprenorphine can help to support treatment adherence. The practice of introducing unconsumed medication directly into urine (known as "spiking" samples) has been increasingly recognized as a potential means to simulate treatment adherence. In the laboratory, examination of the ratios of buprenorphine and its metabolite, norbuprenorphine, has been identified as a mechanism to identify "spiked" samples. Urine levels of naloxone may also be a novel marker in cases where the combination buprenorphine-naloxone product has been administered. This case study, which encompasses one provider's practice spanning two sites, represents a preliminary report on the utility of using urinary naloxone as an indicator of "spiked" urine toxicology samples. Though only a case study, this represents the largest published evaluation of patients' naloxone levels to date.

CASE PRESENTATION

Over a 3-month period across two practice sites, we identified 1,223 patient samples with recorded naloxone levels, spanning a range of 0 to 12,161 ng/ml. The average naloxone level was 633.65 ng/ml with the majority (54%) of samples < 300 ng/ml. 8.0% of samples demonstrated extreme values of naloxone (> 2000 ng/ml). One practice site, which had increased evidence of specimen tampering at collections, had a greater percent of extreme naloxone levels (>  2000 ng/ml) at 9.3% and higher average naloxone level (686.8 ng/ml), in contrast to a second site (570.9 ng/ml; 6.4% at > 2000 ng/ml) that did not have known reports of specimen tampering.

CONCLUSIONS

We postulate that naloxone may serve as an additional flag to identify patient "spiking" of urine samples with use of the combination product of buprenorphine-naloxone.

Urine is superior to oral fluid for detecting buprenorphine compliance in patients undergoing treatment for opioid addiction

BACKGROUND

Buprenorphine (BUP) is commonly used in opioid agonist medication-assisted treatment (OA-MAT). Oral fluid (OF) is an attractive option for compliance monitoring during OA-MAT as collections are observed and evidence suggests that OF is less likely to be adulterated than urine (UR). However, the clinical and analytical performance of each matrix for monitoring BUP compliance has not been well studied.

METHODS

We collected 260 paired OF and UR specimens. Concentrations of buprenorphine (BUP) and norbuprenorphine (NBUP) were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in each matrix. The glucuronide metabolites and naloxone concentrations were also measured in UR by LC-MS/MS. Medications were reviewed and UR creatinine concentrations were determined.

RESULTS

147/260 specimens (57%) were positive for BUP and/or metabolites in one or both matrices. BUP and/or metabolites were more likely to be detected in UR (p < 0.001). 1 OF specimen and 12 UR specimens were considered adulterated/substituted. The majority of patients prescribed BUP were positive for BUP in UR (97%) as opposed to OF (78%). The detection of undisclosed use approximately doubled in UR.

CONCLUSIONS

UR is the preferred matrix for detecting both buprenorphine compliance and undisclosed use. Clinicians should consider the ease of collection, risk of adulteration and detection of illicit drug use when deciding on an appropriate matrix. If OF testing is clinically necessary, UR should be measured in conjunction with OF at least periodically to avoid false negative BUP results.

Positivity rates of drugs in patients treated for opioid dependence with buprenorphine: A comparison of oral fluid and urine using paired collections and LC-MS/MS

BACKGROUND

Drug testing is recommended as part of comprehensive monitoring for medication-assisted treatment. Alternative matrices including oral fluid offer a number of advantages when compared with conventional urine testing but are not as well characterized. This study aims to compare positivity rates of drugs and drug classes in oral fluid and urine as a measure of the clinical utility of oral fluid in the evaluation and treatment of patients with opioid use disorders.

METHODS

A retrospective review of paired oral fluid and urine test results from Millennium Health's laboratory database was performed for 2746 patients with reported prescriptions for buprenorphine products used in the treatment of opioid dependence. Specimens were tested using quantitative LC-MS/MS for 34 medications, metabolites and illicit drugs.

RESULTS

A number of medications and illicit drugs were detected at comparable or higher rates in oral fluid vs. urine such as cocaine (15.7% vs. 7.9%), opiates (13.4% vs. 10.0%), oxycodone (8.6% vs. 3.7%), hydrocodone (3.0% vs. 1.2%) and others. Lower detection rates were observed in oral fluid vs. urine for benzodiazepines (6.6% vs. 8.7%), cannabinoids (15.5% vs. 19.5%), oxymorphone (1.8% vs. 3.1%) and hydromorphone (0.8% vs. 4.5%).

CONCLUSIONS

Clinicians may find oral fluid advantageous for detection of specific drugs and medications in certain clinical situations. Understanding the relative differences between urine and oral fluid can help clinicians carefully select tests best suited for detection in their respective matrix. To our knowledge, this is the largest inter-matrix patient comparison study using paired collections and direct to definitive testing.

Interpreting quantitative urine buprenorphine and norbuprenorphine levels in office-based clinical practice

BACKGROUND

Quantitative urine buprenorphine testing is used to monitor patients receiving buprenorphine for the treatment of opioid use disorder (OUD), however the interpretation of urine buprenorphine testing is complex. Currently, interpretation of quantitative buprenorphine testing is guided by data from drug assay development studies and forensic labs rather than clinical treatment cohorts.

METHODS

In this retrospective study, we describe the patterns of urine buprenorphine and norbuprenorphine levels in patients prescribed sublingual buprenorphine for OUD in an office-based addiction treatment clinic. Urine buprenorphine and norbuprenorphine levels were analyzed in patients who reported having adulterated their urine, patients clinically suspected of adulterating their urine, and patients without concern for urine adulteration. Finally, we tested the accuracy of urine buprenorphine, norbuprenorphine, and norbuprenorphine: buprenorphine ratio (Norbup:Bup) to identify adulterated urine samples.

RESULTS

Patients without suspicion for urine adulteration rarely provided specimens with buprenorphine >=1000ng/ml (4.4%), while the proportion provided by those who endorsed or were suspected of urine adulteration was higher (42.9%, 40.6%, respectively). Compared to patients without reported urine adulteration, specimens from patients who reported or were suspected of urine adulteration had significantly higher buprenorphine (p=0.0001) and lower norbuprenorphine (<0.0001) levels, and significantly lower Norbup:Bup ratios (p=0.04). Buprenorphine >=700ng/ml offered the best accuracy for discriminating between adulterated and non-adulterated specimens.

CONCLUSION

This study describes the patterns of urine buprenorphine and norbuprenorphine levels from patients with OUD receiving buprenorphine treatment in an office-based addiction treatment clinic. Parameters for identifying urine adulterated by submerging buprenorphine medication in the urine specimen are discussed.

Quantitation of Buprenorphine, Norbuprenorphine, Buprenorphine Glucuronide, Norbuprenorphine Glucuronide, and Naloxone in Urine by LC-MS/MS

Buprenorphine is an opioid drug that has been used to treat opioid dependence on an outpatient basis, and is also prescribed for managing moderate to severe pain. Some formulations of buprenorphine also contain naloxone to discourage misuse. The major metabolite of buprenorphine is norbuprenorphine. Both compounds are pharmacologically active and both are extensively metabolized to their glucuronide conjugates, which are also active metabolites. Direct quantitation of the glucuronide conjugates in conjunction with free buprenorphine, norbuprenorphine, and naloxone in urine can distinguish compliance with prescribed therapy from specimen adulteration intended to mimic compliance with prescribed buprenorphine. This chapter quantitates buprenorphine, norbuprenorphine, their glucuronide conjugates and naloxone directly in urine by liquid chromatography tandem mass spectrometry (LC-MS/MS). Urine is pretreated with formic acid and undergoes solid phase extraction (SPE) prior to analysis by LC-MS/MS.

Endogenous opiates and behavior: 2012

This paper is the thirty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2012 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

The challenges of LC–MS/MS analysis of opiates and opioids in urine

Opioids are some of the most commonly prescribed and abused drugs around the world. Primarily used for anesthesia or pain management, other opioids can also be used in the treatment of opioid addiction. Given these facts, clinicians often randomly test or monitor their patients to determine compliance or abstinence from these drugs via immunoassay methods. When a positive screen is obtained, a confirmatory assay is carried out and although the gold standard has been GC–MS, LC–MS/MS is fast becoming a valid and popular alternative. This review will discuss opioids, the complex metabolic pathways, the measurement of these drugs, the challenges involved and, finally, will describe some LC–MS/MS methods published from 2003 until 2013.

High-sensitivity analysis of buprenorphine, norbuprenorphine, buprenorphine glucuronide, and norbuprenorphine glucuronide in plasma and urine by liquid chromatography-mass spectrometry

A new method using ultra-fast liquid chromatography and tandem mass spectrometry (UFLC-MS/MS) was developed for the simultaneous determination of buprenorphine and the metabolites norbuprenorphine, buprenorphine-3β-glucuronide, and norbuprenorphine-3β-glucuronide in plasma and urine. Sample handling, sample preparation and solid-phase extraction procedures were optimized for maximum analyte recovery. All four analytes of interest were quantified by positive ion electrospray ionization tandem mass spectrometry after solid-phase microextraction. The lower limits of quantification in plasma were 1pg/mL for buprenorphine and buprenorphine glucuronide, and 10pg/mL for norbuprenorphine and norbuprenorphine glucuronide. The lower limits of quantitation in urine were 10pg/mL for buprenorphine, norbuprenorphine and their glucuronides. Overall extraction recoveries ranged from 68-100% in both matrices. Interassay precision and accuracy was within 10% for all four analytes in plasma and within 15% in urine. The method was applicable to pharmacokinetic studies of low-dose buprenorphine.

Laboratory testing for prescription opioids

Opioid analgesic misuse has risen significantly over the past two decades, and these drugs now represent the most commonly abused class of prescription medications. They are a major cause of poisoning deaths in the USA exceeding heroin and cocaine. Laboratory testing plays a role in the detection of opioid misuse and the evaluation of patients with opioid intoxication. Laboratories use both immunoassay and chromatographic methods (e.g., liquid chromatography with mass spectrometry detection), often in combination, to yield high detection sensitivity and drug specificity. Testing methods for opioids originated in the workplace-testing arena and focused on detection of illicit heroin use. Analysis for a wide range of opioids is now required in the context of the prescription opioid epidemic. Testing methods have also been primarily based upon urine screening; however, methods for analyzing alternative samples such as saliva, sweat, and hair are available. Application of testing to monitor prescription opioid drug therapy is an increasingly important use of drug testing, and this area of testing introduces new interpretative challenges. In particular, drug metabolism may transform one clinically available opioid into another. The sensitivity of testing methods also varies considerably across the spectrum of opioid drugs. An understanding of opioid metabolism and method sensitivity towards different opioid drugs is therefore essential to effective use of these tests. Improved testing algorithms and more research into the effective use of drug testing in the clinical setting, particularly in pain medicine and substance abuse, are needed.

Metabolic and toxicological considerations of the opioid replacement therapy and analgesic drugs: methadone and buprenorphine

INTRODUCTION

Methadone and buprenorphine are maintenance replacement therapies for opioid dependence; they are also used for pain management. Methadone and buprenorphine (to a lesser extent) have seen sharp increases in mortality associated with their use. They have distinct routes of metabolism (mostly cytochrome P450 dependent), and distinct pharmacologic activity of metabolites. As such, metabolism may play a role in differences in their toxicity.

AREAS COVERED

This article reviews peer-reviewed literature obtained from PubMed searches and literature referenced within. The review considers first an overview of drug use and mortality over the past decade. It then provides extensive detail on the in vitro and in vivo human metabolism of methadone and buprenorphine. Using both human and experimental animal studies it then presents the pharmacodynamic activity of parent drug and metabolites at the mu-opioid receptor, as P-glycoprotein substrates and plasma/brain concentration ratios, and activity at the hERG K(+) channel. Lessons learned from drug interaction studies in humans are then examined in an attempt to bring together the combined information.

EXPERT OPINION

The use and misuse of these drugs contributes to the epidemic in opioid-associated mortalities. A better understanding of metabolism-, transport- and co-medication-induced changes will contribute to their safer use.