Hydromorphone metabolites: isolation and identification from pooled urine samples of a cancer patient

Hydrocodone, Oxycodone, and Morphine Metabolism and Drug-Drug Interactions

Awareness of drug interactions involving opioids is critical for patient treatment as they are common therapeutics used in numerous care settings, including both chronic and disease-related pain. Not only do opioids have narrow therapeutic indexes and are extensively used, but they have the potential to cause severe toxicity. Opioids are the classical pain treatment for patients who suffer from moderate to severe pain. More importantly, opioids are often prescribed in combination with multiple other drugs, especially in patient populations who typically are prescribed a large drug regimen. This review focuses on the current knowledge of common opioid drug-drug interactions (DDIs), focusing specifically on hydrocodone, oxycodone, and morphine DDIs. The DDIs covered in this review include pharmacokinetic DDI arising from enzyme inhibition or induction, primarily due to inhibition of cytochrome p450 enzymes (CYPs). However, opioids such as morphine are metabolized by uridine-5'-diphosphoglucuronosyltransferases (UGTs), principally UGT2B7, and glucuronidation is another important pathway for opioid-drug interactions. This review also covers several pharmacodynamic DDI studies as well as the basics of CYP and UGT metabolism, including detailed opioid metabolism and the potential involvement of metabolizing enzyme gene variation in DDI. Based upon the current literature, further studies are needed to fully investigate and describe the DDI potential with opioids in pain and related disease settings to improve clinical outcomes for patients. SIGNIFICANCE STATEMENT: A review of the literature focusing on drug-drug interactions involving opioids is important because they can be toxic and potentially lethal, occurring through pharmacodynamic interactions as well as pharmacokinetic interactions occurring through inhibition or induction of drug metabolism.

Pharmacogenetic Analysis Enables Optimization of Pain Therapy: A Case Report of Ineffective Oxycodone Therapy

Patients suffering from chronic pain may respond differently to analgesic medications. For some, pain relief is insufficient, while others experience side effects. Although pharmacogenetic testing is rarely performed in the context of analgesics, response to opiates, non-opioid analgesics, and antidepressants for the treatment of neuropathic pain can be affected by genetic variants. We describe a female patient who suffered from a complex chronic pain syndrome due to a disc hernia. Due to insufficient response to oxycodone, fentanyl, and morphine in addition to non-steroidal anti-inflammatory drug (NSAID)-induced side effects reported in the past, we performed panel-based pharmacogenotyping and compiled a medication recommendation. The ineffectiveness of opiates could be explained by a combined effect of the decreased activity in cytochrome P450 2D6 (CYP2D6), an increased activity in CYP3A, and an impaired drug response at the µ-opioid receptor. Decreased activity for CYP2C9 led to a slowed metabolism of ibuprofen and thus increased the risk for gastrointestinal side effects. Based on these findings we recommended hydromorphone and paracetamol, of which the metabolism was not affected by genetic variants. Our case report illustrates that an in-depth medication review including pharmacogenetic analysis can be helpful for patients with complex pain syndrome. Our approach highlights how genetic information could be applied to analyze a patient's history of medication ineffectiveness or poor tolerability and help to find better treatment options.

Pharmacokinetics of hydromorphone hydrochloride after intramuscular and intravenous administration of a single dose to orange-winged Amazon parrots (Amazona amazonica)

OBJECTIVE

To evaluate the pharmacokinetics of hydromorphone hydrochloride after IM and IV administration to orange-winged Amazon parrots (Amazona amazonica).

ANIMALS

8 orange-winged Amazon parrots (4 males and 4 females).

PROCEDURES

Hydromorphone (1 mg/kg) was administered once IM. Blood samples were collected 5 minutes and 0.5, 1.5, 2, 3, 6, and 9 hours after drug administration. Plasma hydromorphone concentrations were determined with liquid chromatography-tandem mass spectrometry, and pharmacokinetic parameters were calculated with a compartmental model. The experiment was repeated 1 month later with the same dose of hydromorphone administered IV.

RESULTS

Plasma hydromorphone concentrations were > 1 ng/mL for 6 hours in 8 of 8 and 6 of 7 parrots after IM and IV injection, respectively. After IM administration, mean bioavailability was 97.6%, and mean maximum plasma concentration was 179.1 ng/mL 17 minutes after injection. Mean volume of distribution and plasma drug clearance were 4.24 L/kg and 64.2 mL/min/kg, respectively, after IV administration. Mean elimination half-lives were 1.74 and 1.45 hours after IM and IV administration, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Hydromorphone hydrochloride had high bioavailability and rapid elimination after IM administration, with rapid plasma clearance and a large volume of distribution after IV administration in orange-winged Amazon parrots. Drug elimination half-lives were short. Further pharmacokinetic studies of hydromorphone and its metabolites, including investigation of multiple doses, different routes of administration, and sustained-release formulations, are recommended.

Pharmacokinetics of hydromorphone hydrochloride after intravenous and intramuscular administration in guinea pigs (Cavia porcellus)

OBJECTIVE

To determine the pharmacokinetics of hydromorphone hydrochloride after IV and IM administration in guinea pigs (Cavia porcellus).

ANIMALS

8 healthy adult guinea pigs (4 sexually intact females and 4 sexually intact males).

PROCEDURES

In a crossover study, hydromorphone (0.3 mg/kg) was administered once IM (epaxial musculature) or IV (cephalic catheter) to each guinea pig at a 1-week interval (2 treatments/guinea pig). Blood samples were collected before and at predetermined intervals after drug administration via a vascular access port. Plasma hydromorphone concentrations were determined by liquid chromatography-tandem mass spectrometry. Noncompartmental analysis of data was used to calculate pharmacokinetic parameters.

RESULTS

Mean ± SD clearance and volume of distribution for hydromorphone administered IV were 52.8 ± 13.5 mL/min/kg and 2.39 ± 0.479 L/kg, respectively. Mean residence time determined for the IV and IM administration routes was 0.77 ± 0.14 hours and 0.99 ± 0.34 hours, respectively. The maximum observed plasma concentration following IM administration of hydromorphone was 171.9 ± 29.4 ng/mL. No sedative effects were observed after drug administration by either route.

CONCLUSIONS AND CLINICAL RELEVANCE

Pharmacokinetic data indicated that hydromorphone at a dose of 0.3 mg/kg may be administered IV every 2 to 3 hours or IM every 4 to 5 hours to maintain a target plasma concentration between 2 and 4 ng/mL in guinea pigs. Hydromorphone had high bioavailability after IM administration. Further research is necessary to evaluate the effects of other doses and administration routes and the analgesic effects of hydromorphone in guinea pigs.

Computational Models Using Multiple Machine Learning Algorithms for Predicting Drug Hepatotoxicity with the DILIrank Dataset

Drug-induced liver injury (DILI) remains one of the challenges in the safety profile of both authorized and candidate drugs, and predicting hepatotoxicity from the chemical structure of a substance remains a task worth pursuing. Such an approach is coherent with the current tendency for replacing non-clinical tests with in vitro or in silico alternatives. In 2016, a group of researchers from the FDA published an improved annotated list of drugs with respect to their DILI risk, constituting “the largest reference drug list ranked by the risk for developing drug-induced liver injury in humans” (DILIrank). This paper is one of the few attempting to predict liver toxicity using the DILIrank dataset. Molecular descriptors were computed with the Dragon 7.0 software, and a variety of feature selection and machine learning algorithms were implemented in the R computing environment. Nested (double) cross-validation was used to externally validate the models selected. A total of 78 models with reasonable performance were selected and stacked through several approaches, including the building of multiple meta-models. The performance of the stacked models was slightly superior to other models published. The models were applied in a virtual screening exercise on over 100,000 compounds from the ZINC database and about 20% of them were predicted to be non-hepatotoxic.

Pain Management in Pediatric Chronic Kidney Disease

Pain is a common problem in children with chronic kidney disease (CKD); however, limited data exist regarding its management. Although most pain is managed pharmacologically, in some instances non-pharmacologic management can aid in safely ameliorating discomfort. Because of the accumulation of toxic metabolites, many common pain medications have adverse effects on kidney function or altered pharmacokinetics in the setting of CKD. Decreased clearance impacts safe dosing of analgesics. The pain management of patients on renal replacement therapy requires an understanding of drug clearance due to the different modalities of dialysis. This educational review highlights pain medications that are safe, albeit often with adjusted dosing, as well as drugs best avoided in the management of pediatric kidney disease. Acetaminophen should be used as a first-line therapy for pain management in children with CKD. Opioids may be added to control moderate to severe pain. Although data are currently lacking, buprenorphine holds promise as a potentially useful drug for the treatment of pain in pediatric patients with CKD. The addition of adjuvant pain medications and non-pharmacologic therapies maybe also be helpful. Despite these options, pain often remains difficult to treat in children with CKD.

Exposure to phthalates and bisphenol A are associated with atopic dermatitis symptoms in children: a time-series analysis

BACKGROUND

Despite increasing evidence on the relationship between exposure to phthalates and bisphenol A with allergies and asthma, reports on atopic dermatitis (AD) with these chemicals are few. We assessed the association between AD symptoms and the exposure to phthalates and bisphenol A and in children.

METHODS

We surveyed 18 boys with AD (age 3-7 years) in a day care center in Seoul between May 2009 and April 2010. AD symptoms were recorded by using a daily symptom diary. We collected 460 series of pooled urine twice a day, in the morning and afternoon, over 230 working days and measured the concentrations of mono-2-ethyl-5-oxohexyl phthalate (5-oxo-MEHP), mono-2-ethyl-5-hydroxyhexyl phthalate (5-OH-MEHP), mono-isobutyl phthalate (MnBP) and bisphenol A glucuronide (BPAG) in the pooled urine. Logistic regression was used for statistical analysis.

RESULTS

Most phthalate metabolite levels were higher in the morning than in the afternoon (p < 0.0001). There was seasonal variation in the levels of phthalates and bisphenol A metabolites. Levels of 5-OH-MEHP, MnBP, and BPAG were highest in summer (p < 0.0001). Manifestation of AD symptoms was associated with an increase in urinary levels of MnBP (adjusted odds ratio, aOR = 2.85, 95% CI: 1.12-7.26 per 1 μg/L of MnBP) and BPAG (aOR = 1.79, 95% CI: 0.91-3.52 per 1 μg/L BPAG) on the same day. The levels of MnBP and BPAG in the previous day increased AD symptoms (aOR = 2.74, 95% CI: 1.21-6.20, for 1 μg/L of MnBP and aOR = 2.01, 95% CI: 1.08-3.74 for 1 μg/L BPAG).

CONCLUSION

Our results suggest that exposure to phthalates and bisphenol A is associated with aggravation of AD symptoms in children.

A Myoclonic Reaction with Low-Dose Hydromorphone

Objective:

To report a case of myoclonus associated with the use of a low dose of the opioid analgesic hydromorphone.

Case Summary:

A 55-year-old white man with a history of nonobstructive hypertrophic cardiomyopathy was hospitalized for treatment of severe chest pain. On hospital day 1, intravenous hydromorphone (6 doses, total dose of 4 mg) was administered. The pain continued and, on day 2, the dose was increased, with a total of 6 mg administered on day 2. The patient developed uncontrollable jerking movements of the head, neck, arms, and legs after he received the hydromorphone. The myoclonic movements stopped within a few hours following discontinuation of hydromorphone and did not recur.

Discussion:

Myoclonus is a neuroexcitatory symptom that has been reported with chronic, high-dose administration of hydromorphone in patients with impaired renal function. The hydromorphone-3-glucuronide metabolite is devoid of analgesic activity and has been shown to cause neuroexcitatory effects. This patient's symptoms appeared soon after hydromorphone was initiated and resolved in a timely manner after the medication was discontinued. Based on the patient's presentation and course of therapy, it is probable, as indicated by the Naranjo probability scale, that the myoclonic symptoms were induced by hydromorphone. This case was unique, however, in that the patient received hydromorphone for only a short duration and did not have impaired renal function.

Conclusions:

Neuroexcitatory effects of hydromorphone may occur at relatively low doses in patients without renal dysfunction. Early recognition and intervention are required to achieve resolution of these symptoms and prevent further sequelae to the patient.

Prescription Opioids. VI. Metabolism and Excretion of Hydromorphone in Urine Following Controlled Single-Dose Administration

Hydromorphone (HM), a prescription opioid and metabolite of morphine and hydrocodone, has been included in proposed revisions to the Mandatory Guidelines for Federal Workplace Drug Testing Programs. This study characterized the time course of HM in hydrolyzed and non-hydrolyzed urine specimens. Twelve healthy subjects were administered a single 8 mg controlled-release HM dose, followed by periodic collection of pooled urine specimens for 54 h following administration. Analysis of total and free HM was conducted by liquid chromatography tandem mass spectrometry at a 50 ng/mL limit of quantitation. Detection periods were determined over a range of thresholds from 50 to 2,000 ng/mL. HM was detected in 85.3% and 47.6% of hydrolyzed and non-hydrolyzed post-dose specimens, respectively. Initial detection of total HM was frequently observed in the first 4-6 h following dosing. The period of detection at the 50 ng/mL threshold averaged 52.3 h for total HM and 38.0 h for free HM. These data support that HM detection is optimized by using low thresholds (50-100 ng/mL) and including conjugated HM in the analysis.

Sulfation of opioid drugs by human cytosolic sulfotransferases: metabolic labeling study and enzymatic analysis

The current study was designed to examine the sulfation of eight opioid drugs, morphine, hydromorphone, oxymorphone, butorphanol, nalbuphine, levorphanol, nalorphine, and naltrexone, in HepG2 human hepatoma cells and human organ samples (lung, liver, kidney, and small intestine) and to identify the human SULT(s) responsible for their sulfation. Analysis of the spent media of HepG2 cells, metabolically labeled with [35S]sulfate in the presence of each of the eight opioid drugs, showed the generation and release of corresponding [35S]sulfated derivatives. Five of the eight opioid drugs, hydromorphone, oxymorphone, butorphanol, nalorphine, and naltrexone, appeared to be more strongly sulfated in HepG2 cells than were the other three, morphine, nalbuphine, and levorphanol. Differential sulfating activities toward the opioid drugs were detected in cytosol or S9 fractions of human lung, liver, small intestine, and kidney, with the highest activities being found for the liver sample. A systematic analysis using eleven known human SULTs and kinetic experiment revealed SULT1A1 as the major responsible SULTs for the sulfation of oxymorphone, nalbuphine, nalorphine, and naltrexone, SULT1A3 for the sulfation of morphine and hydromorphone, and SULT2A1 for the sulfation of butorphanol and levorphanol. Collectively, the results obtained imply that sulfation may play a significant role in the metabolism of the tested opioid drugs in vivo.

The metabolism of opioid agents and the clinical impact of their active metabolites

BACKGROUND

The metabolism of opioids is critical to consider for multiple reasons. The most commonly prescribed opioid agents often have metabolites that are active and are the source of both analgesic activity and an increased incidence of adverse events. Many opioids are metabolized by cytochrome P450 enzymes. Polymorphisms in cytochrome P450 genes and inhibition or induction of cytochrome P450 enzymes by coadministered drugs may significantly impact the systemic concentration of opioids and their metabolites and the associated efficacy or adverse events.

METHODS

This is a narrative review of the metabolism of various opioids that will highlight the impact of their active metabolites, and the potential impact of cytochrome P450 activity on analgesic activity.

RESULTS

An understanding of "opioid metabolic machinery," cytochrome P450 activity, and drug-drug interactions in the context of opioid selection may benefit clinicians and patients alike.

CONCLUSIONS

A greater appreciation of the metabolism of commonly prescribed opioid analgesics and the impact of their active metabolites on efficacy and safety may aid prescribers in tailoring care for optimal outcomes.

A systematic review of the use of opioid medication for those with moderate to severe cancer pain and renal impairment: a European Palliative Care Research Collaborative opioid guidelines project

BACKGROUND

Opioid use in patients with renal impairment can lead to increased adverse effects. Opioids differ in their effect in renal impairment in both efficacy and tolerability. This systematic literature review forms the basis of guidelines for opioid use in renal impairment and cancer pain as part of the European Palliative Care Research Collaborative's opioid guidelines project.

OBJECTIVE

The objective of this study was to identify and assess the quality of evidence for the safe and effective use of opioids for the relief of cancer pain in patients with renal impairment and to produce guidelines.

SEARCH STRATEGY

The Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, MedLine, EMBASE and CINAHL were systematically searched in addition to hand searching of relevant journals.

SELECTION CRITERIA

Studies were included if they reported a clinical outcome relevant to the use of selected opioids in cancer-related pain and renal impairment. The selected opioids were morphine, diamorphine, codeine, dextropropoxyphene, dihydrocodeine, oxycodone, hydromorphone, buprenorphine, tramadol, alfentanil, fentanyl, sufentanil, remifentanil, pethidine and methadone. No direct comparator was required for inclusion. Studies assessing the long-term efficacy of opioids during dialysis were excluded.

DATA COLLECTION AND ANALYSIS

This is a narrative systematic review and no meta-analysis was performed. The Grading of RECOMMENDATIONS Assessment, Development and Evaluation (GRADE) approach was used to assess the quality of the studies and to formulate guidelines.

MAIN RESULTS

Fifteen original articles were identified. Eight prospective and seven retrospective clinical studies were identified but no randomized controlled trials. No results were found for diamorphine, codeine, dihydrocodeine, buprenorphine, tramadol, dextropropoxyphene, methadone or remifentanil.

CONCLUSIONS

All of the studies identified have a significant risk of bias inherent in the study methodology and there is additional significant risk of publication bias. Overall evidence is of very low quality. The direct clinical evidence in cancer-related pain and renal impairment is insufficient to allow formulation of guidelines but is suggestive of significant differences in risk between opioids.

RECOMMENDATIONS

RECOMMENDATIONS regarding opioid use in renal impairment and cancer pain are made on the basis of pharmacokinetic data, extrapolation from non-cancer pain studies and from clinical experience. The risk of opioid use in renal impairment is stratified according to the activity of opioid metabolites, potential for accumulation and reports of successful or harmful use. Fentanyl, alfentanil and methadone are identified, with caveats, as the least likely to cause harm when used appropriately. Morphine may be associated with toxicity in patients with renal impairment. Unwanted side effects with morphine may be satisfactorily dealt with by either increasing the dosing interval or reducing the 24 hour dose or by switching to an alternative opioid.

Recent advances in the use of opioids for cancer pain

Opioids are the mainstay of treatment for moderate to severe cancer pain. In recent years there have been many advances in the use of opioids for cancer pain. Availability and consumption of opioids have increased and opioids other than morphine (including methadone, fentanyl, oxycodone) have become more widely used. Inter-individual variation in response to opioids has been identified as a significant challenge in the management of cancer pain. Many studies have been published demonstrating the benefits of opioid switching as a clinical maneuver to improve tolerability. Constipation has been recognized as a significant burden in cancer patients on opioids. Peripherally restricted opioid antagonists have been developed for the prevention and management of opioid induced constipation. The phenomenon of breakthrough pain has been characterized and novel modes of opioid administration (transmucosal, intranasal, sublingual) have been explored to facilitate improved management of breakthrough cancer pain. Advances have also been made in the realm of molecular biology. Pharmacogenetic studies have explored associations between clinical response to opioids and genetic variation at a DNA level. To date these studies have been small but future research may facilitate prospective prediction of response to individual drugs.

An open-label, 1-year extension study of the long-term safety and efficacy of once-daily OROS(R) hydromorphone in patients with chronic cancer pain

Background

Opioid analgesics have proven efficacy in the short-term management of chronic cancer pain, but data on their long-term use is more limited. OROS^® hydromorphone is a controlled-release formulation of oral hydromorphone that may be particularly well suited to long-term management of chronic cancer pain because it provides stable plasma concentrations and consistent analgesia with convenient once-daily dosing. The objective of this study (DO-118X) was to characterise the pain control achieved with long-term repeated dosing of OROS^® hydromorphone in patients with chronic cancer pain.

Methods

In this multicentre, phase III, open-label, single treatment, 1-year extension study, OROS^® hydromorphone was administered to 68 patients with moderate-to-severe chronic cancer pain, who had successfully completed a short-term equivalence study, and whose pain was controlled with a stable dose of medication (≥ 8 mg OROS^® hydromorphone or equivalent controlled-release morphine). Patients were started on the dose of OROS^® hydromorphone equivalent to the opioid dose on which they achieved dose-stable pain control in the equivalence study; dose adjustments were made as necessary and breakthrough pain medication was permitted. Efficacy was assessed with the Brief Pain Inventory (BPI) and patient and investigator global evaluations of treatment effectiveness. No formal statistical analysis was done.

Results

The mean (standard deviation) duration of exposure to study medication was 139 (129.9) days and the mean (standard deviation) average daily consumption of OROS^® hydromorphone was 43.7 (28.14) mg/day. All scores were maintained at a mild to moderate severity throughout the study; however, BPI scores for pain at its worst, pain at its least, pain on average, pain right now, and pain relief were slightly worsened at end point compared with baseline. Mean BPI pain interference with daily activities and patient and investigator global evaluation scores also remained generally stable. Treatment effectiveness was rated as fair to good throughout the study. The most frequently reported adverse events were nausea (n = 24, 35.3%), constipation (n = 22, 32.4%), and vomiting (n = 15, 22.1%).

Conclusion

The results of this extension study suggest that long-term repeated dosing with once-daily OROS^® hydromorphone can be beneficial in the continuing management of persistent, moderate-to-severe cancer pain.

[Differential therapeutic aspects of analgesia with oral sustained-release strong opioids: application intervals, metabolism and immunosuppression]

The oral "around-the clock" administration of sustained-release strong opioids has been recommended for the long-term treatment of patients suffering from chronic severe pain. At present a plethora of products are available in Germany. Modern galenics even allow for only once-daily oral application without clinically relevant negative chronobiological interference. This application scheme has been shown to improve compliance and sleep quality, factors that influence treatment outcome. Randomized controlled studies revealed no relevant differences between the different strong opioids with respect to efficacy and tolerability. However, hydromorphone and oxycodone appear to be advantageous over morphine due to a lack of immunosuppression. Hydromorphone has the additional benefit of a lower risk of intoxication by accumulation of active metabolites in patients with decreased renal function. As a result, although morphine has been regarded as the standard for the treatment of chronic severe pain, hydromorphone and oxycodone may be better and safer alternatives for certain patient groups (e.g. older age, multimorbidity, cancer).

Role of active metabolites in the use of opioids

The opioid class of drugs, a large group, is mainly used for the treatment of acute and chronic persistent pain. All are eliminated from the body via metabolism involving principally CYP3A4 and the highly polymorphic CYP2D6, which markedly affects the drug's function, and by conjugation reactions mainly by UGT2B7. In many cases, the resultant metabolites have the same pharmacological activity as the parent opioid; however in many cases, plasma metabolite concentrations are too low to make a meaningful contribution to the overall clinical effects of the parent drug. These metabolites are invariably more water soluble and require renal clearance as an important overall elimination pathway. Such metabolites have the potential to accumulate in the elderly and in those with declining renal function with resultant accumulation to a much greater extent than the parent opioid. The best known example is the accumulation of morphine-6-glucuronide from morphine. Some opioids have active metabolites but at different target sites. These are norpethidine, a neurotoxic agent, and nordextropropoxyphene, a cardiotoxic agent. Clinicians need to be aware that many opioids have active metabolites that will become therapeutically important, for example in cases of altered pathology, drug interactions and genetic polymorphisms of drug-metabolizing enzymes. Thus, dose individualisation and the avoidance of adverse effects of opioids due to the accumulation of active metabolites or lack of formation of active metabolites are important considerations when opioids are used.

Capillary electrophoresis contributions to the hydromorphone metabolism in man

CE-ESI multistage IT-MS (CE-MS(n), n < or = 4) and computer simulation of fragmentation are demonstrated to be effective tools to detect and identify phase I and phase II metabolites of hydromorphone (HMOR) in human urine. Using the same CE conditions as previously developed for the analysis of urinary oxycodone and its metabolites, HMOR and its phase I metabolites produced by N-demethylation, 6-keto-reduction and N-oxidation and phase II conjugates of HMOR and its metabolites formed with glucuronic acid, glucose, and sulfuric acid could be detected in urine samples of a patient that were collected during a pharmacotherapy episode with daily ingestion of 48 mg of HMOR chloride. The CE-MS(n) data obtained with the HMOR standard, synthesized hydromorphol and hydromorphone-N-oxide, and CYP3A4 in vitro produced norhydromorphone were employed to identify the metabolites. This approach led to the identification of previously unknown HMOR metabolites, including HMOR-3O-glucide and various N-oxides, structures for which no standard compounds or mass spectra library data were available. Furthermore, the separation of alpha- and beta-hydromorphol, the stereoisomers of 6-keto-reduced HMOR, was achieved by CE in the presence of the single isomer heptakis(2,3-diacetyl-6-sulfato)-beta-CD. The obtained data indicate that the urinary excretion of alpha-hydromorphol is larger than that of beta-hydromorphol.

Opioid metabolites

The metabolism of opioids closely relates to their chemical structure. Opioids are subject to O-dealkylation, N-dealkylation, ketoreduction, or deacetylation leading to phase-I metabolites. By glucuronidation or sulfatation, phase-II metabolites are formed. Some metabolites of opioids have an activity themselves and contribute to the effects of the parent compound. This can go as far that the main clinical activity is exerted through active metabolites while the parent compounds are only weak agonist at mu-opioid receptors, as in the case of codeine and tilidine. The clinical effects of tramadol also involve an important contribution of its active metabolite. With morphine, the active metabolite morphine-6-glucuronide exerts important clinical opioid effects when it accumulates in the plasma of patients with renal failure. However, after short-term administration of morphine, its contribution to the central nervous effects of morphine is probably poor. Morphine-6-glucuronide has recently been identified to exert important peripheral opioid effects. By this, it may play an important role in the clinical effects of morphine. Several other opioids, such as meperidine and perhaps also morphine and hydromorphone, produce metabolites with neuroexcitatory effects. In sum, the evidence suggests that the metabolites of several opioids account for an important part of the clinical effects that must be considered in clinical practice.

Hydromorphone

Hydromorphone is a semi-synthetic opioid that has been used widely for acute pain, chronic cancer pain and to a lesser extent, in chronic nonmalignant pain. Its pharmacokinetics and pharmacodynamics have been well studied, including immediate release oral preparations, a variety of slow release oral preparations, as well as administration through intravenous, subcutaneous, epidural, intrathecal and other routes. It is known to be metabolized to analgesically inactive metabolites that have been associated with neuroexcitatory states and other toxicity. There is no evidence that hydromorphone has any greater abuse liability than other opioids. Further research is needed to address remaining areas of uncertainty: equianalgesic ratios; relative risk of toxicity compared with other opioids, its use in nonmalignant pain, and the role of specific hydromorophone metabolites in the development of toxicity, particularly in association with organ failure.

Contribution to variability in response to opioids

Opioids are the oldest and most effective agents for the short- and long-term control of severe pain, particularly chronic cancer pain palliation. However, morphine and other opioids display wide variations in pharmacological efficacy and tolerability, and a significant number of patients are unable to achieve adequately controlled pain at doses that do not produce intolerable adverse effects. This article reviews factors that affect the efficacy and tolerability of opioid analgesics and clinical strategies for successful pain mangement.

Opioids in renal failure and dialysis patients

This article reviews the literature pertaining to the metabolism of several of the commonly used opioids, and the known activity of their metabolites. The effect of renal failure on the pharmacokinetics of these drugs and metabolites is then reviewed. Finally, the effect of renal dialysis on opioid drugs and metabolites is reviewed. Based on the review, it is recommended that morphine and codeine are avoided in renal failure/dialysis patients; hydromorphone or oxycodone are used with caution and close monitoring; and that methadone and fentanyl/sufentanil appear to be safe to use. Note is made that the "safe" drugs in renal failure are also the least dialyzable.

Identification and synthesis of norhydromorphone, and determination of antinociceptive activities in the rat formalin test

The main objective of this paper is to report the identification and synthesis of norhydromorphone, a novel metabolite of hydromorphone, and its antinociceptive activities when tested in the formalin test as compared to other known analgesics. In addition, we are reporting for the first time the lack of antinociceptive activities of hydromorphone-3-glucuronide, dihydromorphine-3-glucuronide and dihydroisomorphine-3-glucuronide in the rat formalin test. Norhydromorphone was isolated and identified as a metabolite of hydromorphone in a cancer patient's urine. An authentic standard of norhydromorphone was synthesized. The identity of norhydromorphone in the urine sample was confirmed by comparing the LC retention time and MS ion fragmentation with the synthetic standard using a liquid chromatographic-mass spectrometric-mass spectrometric (LC-MS-MS) assay. Norhydromorphone was found to be a minor metabolite of hydromorphone in the urine. Additionally, the antinociceptive activities of norhydromorphone, hydromorphone, morphine, dihydromorphine, dihydroisomorphine, hydromorphone-3-glucuronide, dihydromorphine-3-glucuronide and dihydroisomorphine-3-glucuronide were determined in the rat formalin test following intraperitoneal (i.p.) administration. Only limited antinociception was observed and no significant increase in antinociception was detected at the three doses tested. The increased polarity of norhydromorphone as compared to hydromorphone due to the primary piperidine nitrogen may make it less favorable to cross the blood-brain-barrier (BBB), which may be partly responsible. In addition, lower intrinsic antinociceptive activity, which remains to be determined, could also contribute to the low antinociception. Our results also show that hydromorphone was five times as potent as morphine in the formalin test, while dihydromorphine and dihydroisomorphine were equipotent to and 36% as potent as morphine, respectively. Hydromorphone-3-glucuronide, dihydromorphine-3-glucuronide and dihydroisomorphine-3-glucuronide did not exhibit any antinociceptive effect at the doses tested. The results further underscore the importance of a free C3-OH to the analgesic effect of morphine alkaloids.

Pharmacokinetic and pharmacodynamic evaluation of intravenous hydromorphone in cats1

This study describes the pharmacokinetics of intravenous hydromorphone in cats and the simultaneous measurement of antinociceptive pharmacodynamic effects using a thermal threshold testing system. Following establishment of a baseline thermal threshold, six adult cats were administered 0.1 mg/kg of hydromorphone intravenously. Thermal threshold testing and blood collection were conducted simultaneously at predetermined time points. Plasma hydromorphone concentrations were determined by a liquid chromatographic-mass spectral method and pharmacokinetic analysis was performed by nonlinear least squares regression analysis. Plasma hydromorphone concentrations declined rapidly over time, and were below the limit of quantification of the assay (LOQ = 1.0 ng/mL) by 360 min. In contrast, thermal thresholds rose from a pretreatment value of 40.9 +/- 0.65 degrees C (mean +/- SEM) to instrument cut-out (55 degrees C) within 15 min and remained significantly elevated from 15-450 min after treatment. Inspection of the data revealed no direct correlation between plasma hydromorphone concentrations and the antinociceptive effect of this drug in cats. These findings support the importance of conducting pharmacokinetic studies in parallel with objective measurements of drug effect.

CYP2D6 and CYP3A4 involvement in the primary oxidative metabolism of hydrocodone by human liver microsomes

AIM

To determine the Michaelis-Menten kinetics of hydrocodone metabolism to its O- and N-demethylated products, hydromorphone and norhydrocodone, to determine the individual cytochrome p450 enzymes involved, and to predict the in vivo hepatic intrinsic clearance of hydrocodone via these pathways.

METHODS

Liver microsomes from six CYP2D6 extensive metabolizers (EM) and one CYP2D6 poor metabolizer (PM) were used to determine the kinetics of hydromorphone and norhydrocodone formation. Chemical and antibody inhibitors were used to identify the cytochrome p450 isoforms catalyzing these pathways. Expressed recombinant cytochrome p450 enzymes were used to characterize further the metabolism of hydrocodone.

RESULTS

Hydromorphone formation in liver microsomes from CYP2D6 EMs was dependent on a high affinity enzyme (Km = 26 microm) contributing 95%, and to a lesser degree a low affinity enzyme (Km = 3.4 mm). In contrast, only a low affinity enzyme (Km = 8.5 mm) formed this metabolite in the liver from the CYP2D6 PM, with significantly decreased hydromorphone formation compared with the livers from the EMs. Norhydrocodone was formed by a single low affinity enzyme (Km = 5.1 mm) in livers from both CYP2D6 EM and PM. Recombinant CYP2D6 and CYP3A4 formed only hydromorphone and only norhydrocodone, respectively. Hydromorphone formation was inhibited by quinidine (a selective inhibitor of CYP2D6 activity), and monoclonal antibodies specific to CYP2D6. Troleandomycin, ketoconazole (both CYP3A4 inhibitors) and monoclonal antibodies specific for CYP3A4 inhibited norhydrocodone formation. Extrapolation of in vitro to in vivo data resulted in a predicted total hepatic clearance of 227 ml x h-1 x kg-1 and 124 ml x h-1 x kg-1 for CYP2D6 EM and PM, respectively.

CONCLUSIONS

The O-demethylation of hydrocodone is predominantly catalyzed by CYP2D6 and to a lesser extent by an unknown low affinity cytochrome p450 enzyme. Norhydrocodone formation was attributed to CYP3A4. Comparison of recalculated published clearance data for hydrocodone, with those predicted in the present work, indicate that about 40% of the clearance of hydrocodone is via non-CYP pathways. Our data also suggest that the genetic polymorphisms of CYP2D6 may influence hydrocodone metabolism and its therapeutic efficacy.

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation. condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2002 to June 2003 is reviewed, with 568 references cited.