A rapid and sensitive LC-MS/MS method for quantifying oxycodone, noroxycodone, oxymorphone and noroxymorphone in human plasma to support pharmacokinetic drug interaction studies of oxycodone.

A sensitive and reliable LC-MS/MS method was developed and validated for the quantification of oxycodone and metabolites in human plasma. The method has a runtime of 6 min and a sensitivity of 0.1 µg/L for all analytes. Sample preparation consisted of protein precipitation. Separation was performed on a Kinetix biphenyl column (2.1 × 100 mm, 1.7 µm), using ammonium formate 5 mm in 0.1% aqueous formic acid and methanol LC-MS grade 100% in gradient elution at a flow rate of 0.4 ml/min. Detection was performed in multiple reaction monitoring mode using positive electrospray ionization. The method was linear over the calibration range of 0.1-25.0 µg/L for oxycodone, noroxycodone and noroxymorphone and 0.1-5.0 µg/L for oxymorphone. The method demonstrated good performance in terms of intra- and interday accuracy (86.5-110.3%) and precision (CV 1.7-9.3%). The criteria for the matrix effect were met (CV < 15%) except for noroxymorphone, for which an additional method was applied to compensate for the matrix effect. Whole blood samples were stable for 4 h at room temperature. Plasma samples were stable for 24 h at room temperature and 3 months at -20°C. Furthermore, the method was successfully applied in a pharmacokinetic drug interaction study of oxycodone and enzalutamide in patients with prostate cancer.

Anesthetic and Analgesic Drug Products Advisory Committee Activity and Decisions in the Opioid-crisis Era.

The United States Food and Drug Administration is tasked with ensuring the efficacy and safety of medications marketed in the United States. One of their primary responsibilities is to approve the entry of new drugs into the marketplace, based on the drug's perceived benefit-risk relationship. The Anesthetic and Analgesic Drug Product Advisory Committee is composed of experts in anesthesiology, pain management, and biostatistics, as well as consumer and industry representatives, who meet several times annually to review new anesthetic-related drugs, those seeking new indications, and nearly every opioid-related application for approval. The following report describes noteworthy activities of this committee since 2017, as it has grappled, along with the Food and Drug Administration, to balance the benefit-risk relationships for individual patients along with the overarching public health implications of bringing additional opioids to market. All anesthesia advisory committee meetings since 2017 will be described, and six will be highlighted, each with representative considerations for potential new opioid formulations or local anesthetics.

Acute kidney injury is common with intravenous abuse of extended-release oral oxymorphone and delayed renal recovery rates are associated with increased KDIGO staging.

AIM: Prescription opioid abuse poses a serious problem in the United States, representing 615 per 100 000 deaths annually. Extended-release oxymorphone (Opana-ER) is an oral opioid pain medication that has recently been found to cause thrombotic microangiopathy when intravenously abused. In this retrospective study, we attempted to determine the prevalence and outcomes of acute kidney injury (AKI) among patients intravenously abusing extended-release oral oxymorphone. METHODS: A query of electronic medical records for 'drug abuse' at an academic medical centre during January 2012 to December 2015 was performed and yielded 2350 patients. Patients were further identified by documented intravenous abuse of extended-release oxymorphone. Patients were stratified based on multiple renal indices and outcomes. Potential confounders were also identified. RESULTS: One hundred and sixty-five patients were found to have a documented history of intravenous abuse of extended-release oral oxymorphone. Prevalence of AKI in this population was a 47.8%. KDIGO stage-I patients consisted of 17.8% of patients with AKI, 40.5% were classified as KDIGO stage-II AKI, and 41.8% were classified as KDIGO stage-III AKI. Among patients with AKI, average age was found to be 37.5 years, 59.4% experienced renal recovery, 56.9% required intensive care unit admission, 13.9% progressed to end-stage renal disease (ESRD), and 7.6% expired during admission. CONCLUSION: Clinicians should be educated to help recognize intravenous abuse of extended-release oral oxymorphone and its associated effects. Our data suggests AKI is common in these patients; higher KDIGO staging appears to be associated with slower rates of renal recovery, increased comorbidities and progression to both CKD and ESRD.

Benzylideneoxymorphone: A new lead for development of bifunctional mu/delta opioid receptor ligands.

Opioid analgesic tolerance remains a considerable drawback to chronic pain management. The finding that concomitant administration of delta opioid receptor (DOR) antagonists attenuates the development of tolerance to mu opioid receptor (MOR) agonists has led to interest in producing bifunctional MOR agonist/DOR antagonist ligands. Herein, we present 7-benzylideneoxymorphone (6, UMB 246) displaying MOR partial agonist/DOR antagonist activity, representing a new lead for designing bifunctional MOR/DOR ligands.

Pharmacokinetics of ammonium sulfate gradient loaded liposome-encapsulated oxymorphone and hydromorphone in healthy dogs.

OBJECTIVE: To evaluate the pharmacokinetics, in dogs, of liposome-encapsulated oxymorphone and hydromorphone made by the ammonium sulfate gradient loading technique (ASG). ANIMALS: Four healthy purpose-bred Beagles aged 9.5 ± 3.2 months and weighing 13.4 ± 2.3 kg. STUDY DESIGN: Randomized cross-over design. METHODS: Each dog was given either 4.0 mg kg(-1) of ASG-oxymorphone or 8.0 mg kg(-1) of ASG-hydromorphone SC on separate occasions with a 3-month washout period. Blood was collected at baseline and at serial time points up to 1032 hours (43 days) after injection for determination of serum opioid concentrations. Serum opioid concentrations were measured with HPLC-MS and pharmacokinetic parameters were calculated using commercial software and non-compartmental methods. RESULTS: Serum concentrations of oxymorphone remained above the limit of quantification for 21 days, while those for hydromorphone remained above the limit of quantification for 29 days. Cmax for ASG-oxymorphone was 7.5 ng mL(-1) ; Cmax for ASG-hydromorphone was 5.7 ng mL(-1) . CONCLUSIONS AND CLINICAL RELEVANCE: Oxymorphone and hydromorphone, when encapsulated into liposomes using the ammonium sulfate gradient loading technique, result in measureable serum concentrations for between 3 to 4 weeks. This formulation may have promise in the convenient use of opioids for clinical treatment of chronically painful conditions in dogs.

Generation of novel radiolabeled opiates through site-selective iodination.

Tritiated opioid radioligands have proven valuable in exploring opioid binding sites. However, tritium has many limitations. Its low specific activity and limited counting efficiency makes it difficult to examine low abundant, high affinity sites and its disposal is problematic due to the need to use organic scintillants and its relatively long half-life. To overcome these issues, we have synthesized both unlabeled and carrier-free radioiodinated iodobenzoyl derivatives of 6ß-naltrexamine ((125)I-BNtxA, 18), 6ß-naloxamine ((125)I-BNalA, 19) and 6ß-oxymorphamine ((125)I-BOxyA, 20) with specific activities of 2100Ci/mmol. To optimize the utility of the radioligand, we designed a synthesis in which the radiolabel is incorporated in the last synthetic step, which required the selective iodination of the benzoyl moiety without incorporation into the phenolic A ring. Competition studies demonstrated high affinity of the unlabelled compounds for opioid receptors in transfected cell lines, as did the direct binding of the (125)I-ligands to the opioid receptors. The radioligand displayed very high sensitivity, enabling a marked reduction in tissue, as well as excellent signal/noise characteristics. These new (125)I-radioligands should prove valuable in future studies of opioid binding sites.

Determination of morphine and oxymorphone in exhaled breath condensate samples: Application of microwave enhanced three-component deep eutectic solvent-based air-assisted liquid-liquid microextraction and derivatization prior to gas chromatography-mass spectrometry.

In this work, a microwave-enhanced air-assisted liquid-liquid microextraction method combined with gas chromatography-mass spectrometry has been developed for morphine and oxymorphone assessment in EBC samples. For this purpose, choline chloride-menthol-phenylacetic acid deep eutectic solvent (as an extraction solvent), butyl chloroformate (as a derivatization agent), and picoline (as a catalyst) are used. After performing predetermined extraction cycles in the microextraction method, the obtained cloudy solution is exposed to microwave irradiations to enhance extraction and derivatization efficiencies. The method provided low limits of detection (morphine 2.1 and oxymorphone 1.5 ng mL-1) and quantification (morphine 7.2 and oxymorphone 5.2 ng mL-1) in the EBC samples. The method had proper repeatability, accuracy, and stability expressed as relative standard deviations less than 5.1, 9, and 9%, respectively. The developed method was successfully used to determine morphine and oxymorphone concentrations in the EBC samples of addict patients.

Concentration of oxymorphone in postmortem fluids and tissue.

Oxymorphone, a semi-synthetic opioid analgesic, has been available as Numorphan since the 1950s in the form of injectable solutions and a suppository. Recently, in 2006, oxymorphone was approved by the Federal Drug Administration for use in the form of immediate and extended release tablets under the trade name Opana. Since the advent of Opana, the number of deaths involving oxymorphone has risen considerably in the State of North Carolina. To date, there are very few reported values for postmortem concentrations of oxymorphone in the literature to aid in the interpretation of these cases. We report 33 medical examiner cases involving oxymorphone and provide the distribution of oxymorphone in postmortem blood, liver, and urine samples. Oxymorphone was detected in blood by enzyme immunoassay and confirmed by gas chromatography- mass spectrometry utilizing a solid-phase extraction procedure. Calibration curves from 0.025 to 0.50 mg/L were established with a limit of quantitiation of 0.025 mg/L. The mean concentration for oxymorphone in postmortem central (n = 28) and peripheral (n = 23) blood samples was 0.15 mg/L. The median values for the central and peripheral samples were 0.10 mg/L (range: 0.011-0.59) and 0.075 mg/L (range: 0.017-0.82), respectively. Liver concentrations ranged from "none detected" to > 2.0 mg/kg, with mean and median values of 0.36 and 0.30 mg/kg, respectively. The majority of urine samples were > 0.50 mg/L.

Synthesis, Biological, and Structural Explorations of New Zwitterionic Derivatives of 14- O-Methyloxymorphone, as Potent µ/δ Opioid Agonists and Peripherally Selective Antinociceptives.

Herein, the synthesis and pharmacological characterization of an extended library of differently substituted N-methyl-14- O-methylmorphinans with natural and unnatural amino acids and three dipeptides at position 6 that emerged as potent µ/δ opioid receptor (MOR/DOR) agonists with peripheral antinociceptive efficacy is reported. The current study adds significant value to our initial structure-activity relationships on a series of zwitterionic analogues of 1 (14- O-methyloxymorphone) by targeting additional amino acid residues. The new derivatives showed high binding and potent agonism at MOR and DOR in vitro. In vivo, the new 6-amino acid- and 6-dipeptide-substituted derivatives of 1 were highly effective in inducing antinociception in the writhing test in mice after subcutaneous administration, which was antagonized by naloxone methiodide demonstrating activation of peripheral opioid receptors. Such peripheral opioid analgesics may represent alternatives to presently available drugs for a safer pain therapy.

Use of oral oxymorphone in the elderly.

OBJECTIVE: To review the pharmacodynamics, pharmacokinetics, efficacy, tolerability, dosing, and role of oral oxymorphone immediate-release (IR) and extended-release (ER). DATA SOURCE: A MEDLINE/PUBMED search (1970 to September 2006) of English language studies. Additional references were obtained from their bibliographies. STUDY SELECTION: All human studies of oxymorphone were reviewed. DATA SYNTHESIS: Oral oxymorphone IR/ER tablet formulations were approved in June 2006. Oxymorphone, a semi-synthetic -opioid receptor agonist structurally similar to hydromorphone, has an oral bioavailability of approximately 10%. Oxymorphone is extensively metabolized to oxymorphone-3-glucuronide and the active 6-hydroxyoxymorphone. Rapid clearance mandates every four- to six-hour dosing (IR) and every 12-hour dosing (ER). Hepatic impairment, renal impairment, and aging enhance systemic exposure. Oxymorphone IR was superior to placebo and oxycodone IR (acute pain studies). Oxymorphone ER was superior to placebo and equivalent to oxycodone CR and morphine CR (one acute and five chronic pain studies). Oxymorphone exhibits the expected opioid side effects, being comparable to oxycodone and morphine in clinical trials. Coadministration with ethanol causes "dose-dumping" (ER) and increases intersubject variability in drug absorption. Oxymorphone IR is indicated for the relief of moderate-to-severe pain, while oxymorphone ER is indicated for persistent pain. Initial doses (opioid-naïve) are 10 mg to 20 mg every 4 to 6 hours (IR) and 5 mg every 12 hours (ER). Dosage adjustment is recommended in mild hepatic impairment (Child-Pugh class A), renal impairment (creatinine clearance below 50 mL/min), and in the elderly. CONCLUSION: Oxymorphone is the newest oral opioid to enter a crowded marketplace now totaling 12 Schedule 2 opioids. It does not appear to have any unique assets or liabilities and should be considered as one of many oral opioids for the management of acute and persistent pain of moderate-to-severe intensity.

Abuse of reformulated OxyContin: Updated findings from a sentinel surveillance sample of individuals assessed for substance use disorder.

OBJECTIVE: To examine abuse prevalence for OxyContin and comparator opioids over a 6-year period prior to and following market entry of reformulated OxyContin and assess consistency in abuse across treatment settings and geographic regions. DESIGN: An observational study examining longitudinal changes using cross-sectional data from treatment centers for substance use disorder. SETTING: A total of 874 facilities in 39 states in the United States within the National Addictions Vigilance Intervention and Prevention Program (NAVIPPRO®) surveillance system. PARTICIPANTS: Adults (72,060) assessed for drug problems using the Addiction Severity Index-Multimedia Version (ASI-MV®) from January 2009 through December 2015 who abused prescription opioids. MAIN OUTCOME MEASURE(S): Percent change in past 30-day abuse. RESULTS: OxyContin had significantly lower abuse 5 years after reformulation compared to levels for original OxyContin. Consistency of magnitude in OxyContin abuse reductions across geographic regions, ranging from 41 to 52 percent with differences in abuse reductions in treatment setting categories occurred. Changes in geographic region and treatment settings across study years did not bias the estimate of lower OxyContin abuse through confounding. CONCLUSION: In the postmarket setting, limitations and methodologic challenges in abuse measurement exist and it is difficult to isolate singular impacts of any one intervention given the complexity of prescription opioid abuse. Expectations for a reasonable threshold of abuse for any one ADF product or ADF opioids as a class are still uncertain and undefined. A significant decline in abuse prevalence of reformulated OxyContin was observed 5 years after its reformulation among this treatment sample of individuals assessed for substance use disorder that was lower historically for the original formulation of this product.

Species-specific lipophilicity of morphine antagonists.

Complete sets of microscopic acid-base and partition equilibrium constants were experimentally determined for therapeutically important morphine derivatives, including the widely used antagonists naloxone and naltrexone. The acid-base microequilibria were characterized by combining pH-potentiometry and deductive methods using synthesized auxiliary compounds. Microscopic protonation equilibria show that approximately three times as many zwitterionic microspecies than non-charged ones exist in oxymorphone and naltrexone solutions. On the other hand, the non-charged microspecies is the dominant one in the case of naloxone, although its concentration is only 1.34 times higher than that of its zwitterionic protonation isomer. Partition coefficients of the individual microspecies were determined by a combination of experimentally measured distribution constants and deductive methods. The contribution ratio of the non-charged versus zwitterionic species to the overall lipophilicity is quantified and depicted in terms of species-specific lipophilicities over the entire pH range for each compound. Our lipophilicity values allowed the molecular interpretation of the classical pharmacologic observation that naloxone has a faster onset for antagonist activity, and a concomitant shorter duration of action.

Neurologically active plant compounds and peptide hormones: a chirality connection.

The most dramatic, but seldom mentioned, difference between alkaloid and peptide opioids is the change of chirality of the alpha carbon of the tyramine moiety. We propose that the presence of Gly2 or D-Ala2 in the two most common message domains compensates this change by allowing the attainment of unusual conformations. A thorough conformational search of Tyr-D-Ala-Phe-NH-CH3 and of its isomer Tyr-L-Ala-Phe-NH-CH3 backs this view and establishes a solid link between alkaloid and peptide opioids. This finding supports the notion that morphine, like other neurologically active plant compounds, may bind to endogenous receptors in plants to regulate cell-to-cell signaling systems.

Antagonism in opioid peptides: the role of conformation.

The availability of new, highly selective antagonists, in the field of opioid peptides and of other pain peptides, is important both for a better understanding of the interaction of the receptors with their ligands and for their practical relevance. The design of antagonists is not obvious even when the essential features of agonists are well known. In this review we have examined the main aspects of the problem using, as leading criteria two theoretical models of antagonism and the subdivision of opioid peptides into two functional domains. The main causes of antagonism have been integrated in two very general models: one, referred to as the participation model, attributes antagonism to the lack, with respect to the parent agonist, of an essential group, whereas another model, attributes antagonism to the misfit of the molecule inside the receptor. The second criterion is the division of the structure of peptide hormones, originally put forward by Robert Schwyzer, in two functional domains, the message domain, which is responsible of the larger part of the binding affinity of opioid agonists, and an address domain, which dictates most of the peptide specificity. The most significant achievements in the design of opioid antagonists are classified according to the relative importance of chemical constitution, conformation and chirality.

Identification of opioid ligands possessing mixed micro agonist/delta antagonist activity among pyridomorphinans derived from naloxone, oxymorphone, and hydromorphone [correction of hydropmorphone].

A series of pyridomorphinans derived from naloxone, oxymorphone, and hydromorphone (7a-k) were synthesized and evaluated for binding affinity at the opioid delta, micro, and kappa receptors in brain membranes using radioligand binding assays and for functional activity in vitro using [(35)S]GTP-gamma-S binding assays in brain tissues and bioassays using guinea pig ileum (GPI) and mouse vas deferens (MVD) smooth muscle preparations. The pyridine ring unsubstituted pyridomorphinans possessing the oxymorphone and hydromorphone framework displayed nearly equal binding affinity at the micro and delta receptors. Their affinities at the kappa site were nearly 10-fold less than their binding affinities at the micro and delta sites. Introduction of aryl substituents at the 5'-position on the pyridine ring improved the binding affinity at the delta site while decreasing the binding affinity at the micro site. Nearly all of the ligands possessing an N-methyl group at the17-position with or without a hydroxyl group at the 14-position of the morphinan moiety displayed agonist activity at the micro receptor with varying potencies and efficacies. In the [(35)S]GTP-gamma-S binding assays, most of these pyridomorphinans were devoid of any significant agonist activity at the delta and kappa receptors but displayed moderate to potent antagonist activity at the delta receptors. In antinociceptive evaluations using the warm-water tail-withdrawal assay in mice, the pyridomorphinans produced analgesic effects with varying potencies and efficacies when administered by the intracerebroventricular route. Among the ligands studied, the hydromorphone-derived 4-chlorophenylpyridomorphinan 7h was identified as a ligand possessing a promising profile of mixed micro agonist/delta antagonist activity in vitro and in vivo. In a repeated administration paradigm in which the standard micro agonist morphine produces significant tolerance, repeated administration of the micro agonist/delta antagonist ligand 7h produced no tolerance. These results indicate that appropriate molecular manipulations of the morphinan templates could provide ligands with mixed micro agonist/delta antagonist profiles and such ligands may have the potential of emerging as novel analgesic drugs devoid of tolerance, dependence, and related side effects.

7-spirobenzocyclohexyl derivatives of naltrexone, oxymorphone, and hydromorphone as selective opioid receptor ligands.

On the basis of previous structure-activity studies of the highly potent and selective delta-opioid receptor antagonist naltrindole (1) and the spiroindanyl analogues 2 and 3, we have synthesized epimeric pairs of spirobenzocyclohexyl derivatives of naltrexone, oxymorphone, and hydromorphone (4-9). Pharmacologic evaluation in smooth muscle assays has revealed that the oxymorphone derivatives (6, 7) are delta-selective agonists and possess receptor binding profiles that are consistent with their agonist activity. It is proposed that the spirobenzocyclohexyl group of 6 and 7 orients its benzene moiety orthogonally with respect to the C ring of the opiate in a manner similar to that of the spiroindanyl analogue 3. It is suggested that this orthogonal orientation serves as an "address" to facilitate activation of delta receptors. The finding that the hydromorphone analogues (8, 9) were full mu agonists and exhibited only partial delta agonist activity suggests that the 14-hydroxyl group also contributes to the delta agonist activity. The naltrexone derivatives (4, 5) were mu-selective antagonists and exhibited relatively weak delta antagonist activity. However, the binding data indicated a very high-affinity delta-selective binding profile that was not consistent with the pharmacology. This study illustrates the differential contributions of the delta "address" to agonist and antagonist activity and supports the idea of different recognition sites for interaction of agonist and antagonist ligands with delta-opioid receptors.

Investigation of phenolic bioisosterism in opiates: 3-sulfonamido analogues of naltrexone and oxymorphone.

[formula: see text] The phenolic hydroxy group of opiate-derived ligands is of known importance for biological activity. On the basis of its putative role as a hydrogen-bonding donor in the interaction with opioid receptors, it was replaced with a sulfonamide group because of their similar pKa values. The first thebaine-derived 3-amino (8a, 8b) and subsequent sulfonamide analogues (10a, 10b) were synthesized from naltrexone (1a) and oxymorphone (1b) in a linear nine-step synthesis. The sulfonamides were tested in vitro and found inactive.

In vitro opioid activity profiles of 6-amino acid substituted derivatives of 14-O-methyloxymorphone.

A series of 6-amino acid conjugates (glycine, alanine and phenylalanine) of the highly potent opioid analgesic 14-O-methyloxymorphone was developed in an effort to obtain agonists that would have potentially limited ability to cross the blood-brain barrier. Binding studies revealed that all derivatives displayed high affinities (0.77-2.58 nM) at the mu-opioid receptor in rat brain membranes. They were potent agonists in mouse vas deferens preparation (IC(50)=5.52-26.8 nM). While the alpha-amino acid epimers are favoured by mu-opioid receptors, the beta-epimers proved to have increased interaction with delta-sites. Only the beta-phenylalanine conjugate showed some preference for delta- over mu-opioid receptors and delta-opioid receptor agonist activity. The relatively high delta-opioid receptor affinity of this analogue was also predicted by molecular modelling studies. The newly developed ionizable derivatives could find clinical applications as potent analgesics without the adverse actions of centrally acting opioids.

Transdermal oxymorphone formulation development and methods for evaluating flux and lag times for two skin permeation-enhancing vehicles.

Oxymorphone is a candidate for transdermal delivery since it is a very potent analgesic, is not very effective orally, and has a short duration of action. In developing a transdermal delivery system, two criteria that were considered important were achieving adequate flux and minimizing the lag time. Oxymorphone skin permeation rates in vitro were very low unless skin permeation enhancers were included in the vehicle. After an initial screen of 17 formulations, two skin permeation-enhancing formulations were selected for further study. These were myristic acid:propylene glycol:oxymorphone base (A), and decylmethylsulfoxide:ethanol:water:oxymorphone.HCl (B). With either formulation and either human or hairless guinea pig skin, there was little dependence of either in vitro flux or lag time on the section of skin used (stratum corneum, epidermis, epidermis/dermis). There were significant differences between human skin and hairless guinea pig skin when comparing in vitro fluxes with the two formulations. With formulation A, fluxes through hairless guinea pig skin were three-to fivefold greater than through human skin. With B, however, fluxes through human skin were up to fivefold greater than through hairless guinea pig skin. In vitro lag times with A were generally long (approximately 24 h), whereas those with B were much lower (approximately 1 to 10 h). The species dependence of permeation enhancement and the differences in lag time between formulations could be related to differences in the mechanisms of permeation enhancement. In vivo lag times with the fatty acid:propylene glycol vehicle were estimated in hairless guinea pigs based on plasma oxymorphone concentrations. These were much lower than in vitro lag times.

Forensic drug testing for opiates. VI. Urine testing for hydromorphone, hydrocodone, oxymorphone, and oxycodone with commercial opiate immunoassays and gas chromatography-mass spectrometry.

Opiate testing for morphine and codeine is performed routinely in forensic urine drug-testing laboratories in an effort to identify illicit opiate abusers. In addition to heroin, the 6-keto-opioids, including hydromorphone, hydrocodone, oxymorphone, and oxycodone, have high abuse liability and are self-administered by opiate abusers, but only limited information is available on detection of these compounds by current immunoassay and gas chromatographic-mass spectrometric (GC-MS) methods. In this study, single doses of hydromorphone, hydrocodone, oxymorphone, and oxycodone were administered to human subjects, and urine samples were collected before and periodically after dosing. Opiate levels were determined in a quantitative mode with four commercial immunoassays, TDx opiates (TDx), Abuscreen radioimmunoassay (ABUS), Coat-A-Count morphine in urine (CAC), and EMIT d.a.u. opiate assay (EMIT), and by GC-MS. GC-MS assay results indicated that hydromorphone, hydrocodone, oxymorphone, and oxycodone administration resulted in rapid excretion of parent drug and O-demethylated metabolites in urine. Peak concentrations occurred within 8 h after drug administration and declined below 300 ng/mL within 24-48 h. Immunoassay testing indicated that hydromorphone, hydrocodone, and oxycodone, but not oxymorphone, were detectable in urine by TDx and EMIT (300-ng/mL cutoff) for 6-24 h. ABUS detected only hydrocodone, and CAC failed to detect any of the four 6-keto-opioid analgesics. Generally, immunoassays for opiates in urine displayed substantially lower sensitivities for 6-keto-opioids compared with GC-MS. Consequently, urine samples containing low to moderate concentrations of hydromorphone, hydrocodone, oxymorphone, and oxycodone will likely go undetected when tested by conventional immunoassays.