Pharmacokinetics and Pharmacodynamics of Methadone Enantiomers in Hospice Patients With Cancer Pain

Methadone Serum Concentration Monitoring in Palliative Care Patients with Cancer-Induced Bone Pain: A Short Communication

BACKGROUND

Therapeutic drug monitoring of methadone for opioid replacement therapy in the management of opioid dependence is well-described. However, only a few studies have described the correlation between serum methadone concentration and cancer pain during palliative care.

METHODS

Patients were recruited from an exploratory randomized controlled trial (RCT) comparing methadone rotation with other opioid rotations for refractory cancer-induced bone pain. Serum methadone trough levels and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) levels on day 14 of the rotation were analyzed using validated liquid chromatography-mass spectrometry. The average and worst pain intensities were rated at baseline and on day 14, preceding the recorded methadone levels. The Common Terminology Criteria for Adverse Events composite score was used to determine the adverse effects of methadone. The Spearman ρ was used to examine the correlation between methadone trough levels and pain reduction.

RESULTS

Among the 20 patients who were randomized to receive methadone in the RCT, eight consented to this substudy. The mean (SD) steady-state 24-hour methadone dose was 11.6 (2.6) mg, whereas the mean (SD) serum methadone trough concentration was 93.7 (45.6) ng/mL with an acceptable adverse effect profile. All patients had an EDDP concentration of <0.01 mg/L, suggesting good metabolite clearance.

CONCLUSIONS

The reported methadone concentration required for therapeutic benefit was significantly lower than that reported previously. The study highlights that further appropriately powered studies are required to establish the role of routine trough methadone monitoring in patients newly rotated for the management of refractory cancer pain.

Intravenous methadone in the management of acute postoperative pain in a chronic cancer pain patient: A case report and review of the literature

Key Clinical Message

The current landscape of literature highlights that there is insufficient well-powered and robust evidence to support the integration of intravenous methadone into current guidelines and frameworks in supporting the pain management of cancer patient with complex pain syndromes. However, there is preliminary evidence, both from the literature as well as this case study that highlights intravenous methadone may be efficaciously and safety used for the management of postoperative pain in cancer patients with chronic pain undergoing operative management. Further research is required to fully elucidate key considerations of integrating this medication into clinical practice including consideration into dosing, opioid conversion, tolerance, and safety.

Abstract

Methadone is a broad-spectrum analgesic with long duration of effect. Its multimodal mechanism of action, such as through effects on mu-opioid receptor and presynaptic N-methyl-D-aspartate receptors, has led to its current use in the management of opioid dependence in the community and in palliative care. These properties however make methadone appealing in the management of postoperative pain, particularly for patients with complex analgesic requirements. We report on an interesting case whereby intravenous methadone was effectively used for postoperative analgesia in a 56-year-old female with complex chronic pain secondary to a mucinous pelvic neoplasm of unclear primary who underwent palliative resection. Further, we review the literature surrounding usage of methadone in this setting to understand current challenges and barriers to implementation of methadone as an analgesia option for chronic pain patients following surgery. To do this, a case report and literature review was conducted in accordance to the CARE case report guidelines. The patient provided written consent for the de-identification and use of their medical information and data for the generation and publication of this case report. Our case report and literature review demonstrate there remains significant heterogeneity, unfamiliarity, and scarce use of intravenous methadone in the perioperative and postoperative space in the management of patients with complex pain regimens such as chronic cancer pain patients. Despite this, our case report and literature review highlight as a broad analgesic, intravenous methadone warrants consideration following more rigorous research and development of safe use guidelines into its use for this purpose.

Methadone Switching for Cancer Pain: A New Classification of Initiation Protocols, Based on a Critical Literature Review

Background: The initiation of methadone, a known effective analgesic for cancer pain, is complex. The existing protocols are often inadequately described; therefore, a classification of literature is needed. We reviewed and classified the recent literature on methadone initiation protocols in cancer patients experiencing severe pain. Objective: To provide a new classification of initiation protocols, based on a critical literature review. Data Sources: The MEDLINE database was searched for articles published until March 25, 2021, using the terms "cancer pain," "methadone," "methadone introduction," or "methadone initiation." The search was limited to human studies, randomized controlled trials (RCTs), other clinical trials, meta-analyses, and case reports. Selected articles were assessed for initiation details (rapid or progressive), administered dose (fixed rescue dose or ad libitum), and dose calculation (fixed or progressive ratios using morphine equivalent daily dose [MEDD] for daily or unitary dose). Results: Twenty-four publications that met our inclusion criteria were analyzed. No large-scale prospective double-blind RCTs with robust design were identified. Most studies assessed relatively small numbers of patients. Eight initiation types were identified, of which three involved seven "high quality" studies: "rapid switch-fixed doses and rescue dose-progressive daily ratio," "progressive switch-fixed dose and rescue dose-progressive daily ratio," and "rapid switch-ad libitum-fixed ratio for unitary dose" protocols. This classification provides the latest information on methadone initiation protocols. The total daily dose of methadone varied largely across protocols. Conclusion: We recommend a maximal daily methadone dose of 100 mg (3 doses of 30 mg or 5 doses of 20 mg) for MEDD <500 mg, when the two "ad libitum" protocols are used. Further clinical research on this topic is warranted.

Characterization of the Safety and Pharmacokinetic Profile of D-Methadone, a Novel N-Methyl-D-Aspartate Receptor Antagonist in Healthy, Opioid-Naive Subjects: Results of Two Phase 1 Studies

PURPOSE/BACKGROUND

N-methyl-D-aspartate (NMDA) receptor (NMDAR) antagonists are potential agents for the treatment of several central nervous system disorders including major depressive disorder. Racemic methadone, L-methadone, and D-methadone all bind the NMDAR with an affinity similar to that of established NMDAR antagonists, whereas only L-methadone and racemic methadone bind to opioid receptors with high affinity. Therefore, D-methadone is expected to have no clinically significant opioid effects at therapeutic doses mediated by its NMDAR antagonism.

METHODS

We conducted 2 phase 1, double-blind, randomized, placebo-controlled, single- and multiple-ascending-dose studies to investigate the safety and tolerability of oral D-methadone and to characterize its pharmacokinetic profile in healthy opioid-naive volunteers.

RESULTS

D-Methadone exhibits linear pharmacokinetics with dose proportionality for most single-dose and multiple-dose parameters. Single doses up to 150 mg and daily doses up to 75 mg for 10 days were well tolerated with mostly mild treatment-emergent adverse events and no severe or serious adverse events. Dose-related somnolence and nausea occurred and were mostly present at the higher dose level. There was no evidence of respiratory depression, dissociative and psychotomimetic effects, or withdrawal signs and symptoms upon abrupt discontinuation. An overall dose-response effect was observed, with higher doses resulting in larger QTcF (QT interval corrected using Fridericia formula) changes from baseline, but none of the changes were considered clinically significant by the investigators. Mild, dose-dependent pupillary constriction of brief duration occurred particularly at the 60-mg dose or above in the single-ascending-dose study and at the dose of 75 mg in the multiple-ascending-dose study. No detectable conversion of D-methadone to L-methadone occurred in vivo.

CONCLUSIONS

These results support the safety and continued clinical development of D-methadone as an NMDAR antagonist for the treatment of depression and other central nervous system disorders.

Pharmacologic Treatment of Opioid Use Disorder: a Review of Pharmacotherapy, Adjuncts, and Toxicity

Opioid use disorder continues to be a significant source of morbidity and mortality in the USA and the world. Pharmacologic treatment with methadone and buprenorphine has been shown to be effective at retaining people in treatment programs, decreasing illicit opioid use, decreasing rates of hepatitis B, and reducing all cause and overdose mortality. Unfortunately, barriers exist in accessing these lifesaving medications: users wishing to start buprenorphine therapy require a waivered provider to prescribe the medication, while some states have no methadone clinics. As such, users looking to wean themselves from opioids or treat their opioid dependence will turn to alternative agents. These agents include using prescription medications, like clonidine or gabapentin, off-label, or over the counter drugs, like loperamide, in supratherapeutic doses. This review provides information on the pharmacology and the toxic effects of pharmacologic agents that are used to treat opioid use disorder. The xenobiotics reviewed in depth include buprenorphine, clonidine, kratom, loperamide, and methadone, with additional information provided on lofexidine, akuamma seeds, kava, and gabapentin.

[Opioid switch and change of route of administration in cancer patients treated by morphine]

This paper reviewed the 2002 guidelines established by the National Federation of Cancer Centres. A group of experts nominated by the 3 French Societies involved in the treatment of cancer pain (AFSOS, SFAP, SFETD), established new guidelines ratios for morphine switching and/or changing of route of administration, in patients for whom either pain was not adequatly managed or adverse effects were unbearable. After a rapid reminder of the pharmacokinetics and metabolism properties of morphine, experts explained why the theory of opioid rotation (oxycodone, hydromorphone, fentanyl, methadone, tapentadol) using fixed equianalgesic ratios is not any more appropriate for a secure clinical practice. In the light of recent publications enhancing our knowledge on the efficacy of new drug switching ratios and for changing the route of administration of morphine, the group of experts recommended to use reconsidered switching ratios favoring security upon efficacy, to minimize overdosing and adverse effects. Consequently, after the new conversion ratio (using slow release opioids) was applied, a second titration should be done by means of normal release rescue formulations for breakthrough pain episodes. A smartphone App. OpioConvert^® will be available for rapid and secure dose conversions.

Methadone Recycling Sustains Drug Reservoir in Tissue

We hypothesize that there is a tissue store of methadone content in humans that is not directly accessible, but is quantifiable. Further, we hypothesize the mechanism by which methadone content is sustained in tissue stores involves methadone uptake, storage, and release from tissue depots in the body (recycling). Accordingly, we hypothesize that such tissue stores, in part, determine plasma methadone levels. We studied a random sample of six opioid-naïve healthy subjects. We performed a clinical trial simulation in silico using pharmacokinetic modeling. We found a large tissue store of methadone content whose size was much larger than methadone's size in plasma in response to a single oral dose of methadone 10 mg. The tissue store measured 13-17 mg. This finding could only be explained by the contemporaneous storage of methadone in tissue with dose recycling. We found that methadone recycles 2-5 times through an inaccessible extravascular compartment (IAC), from an accessible plasma-containing compartment (AC), before exiting irreversibly. We estimate the rate of accumulation (or storage) of methadone in tissue was 0.029-7.29 mg/h. We predict 39 ± 13% to 83 ± 6% of methadone's tissue stores "spillover" into the circulation. Our results indicate that there exists a large quantifiable tissue store of methadone in humans. Our results support the notion that methadone in humans undergoes tissue uptake, storage, release into the circulation, reuptake from the circulation, and re-release into the circulation, and that spillover of methadone from tissue stores, in part, maintain plasma methadone levels in humans.

Cross-sectional pilot study to monitor the availability, dispensed prices, and affordability of opioids around the globe

CONTEXT

Opioids are essential medicines. The World Health Organization and Health Action International monitor the price of essential medicines. However, their surveys do not include opioids, and there is no information on their affordability.

OBJECTIVES

To provide information on access to pain treatment, as measured by the availability and dispensed price of five opioids in 13 formulations, and the affordability of oral immediate-release (IR) morphine.

METHODS

The International Association for Hospice and Palliative Care members were distributed by their countries' Gross National Income (GNI) level using the World Bank categories, i.e., high income country (HIC), upper middle income country (UMIC), lower middle income country (LMIC), low income country (LIC), and randomized. A total of 10 participants were selected from each (n=40) domain. Participants were asked to identify a pharmacy located closest to a public facility that provides diagnosis/treatment for life-threatening conditions and report the lowest dispensed price of the smallest selling unit and strength of each formulation. Availability and median (Me) price were calculated for each. Affordability and percentage of international buyer price (IBP) were calculated for morphine oral solid IR.

RESULTS

A total of 30 participants from 26 countries (response rate=75%) responded. Significant correlation was found between availability and GNI (range: 65-68% [HIC and LIC]; R=0.781; P<0.0001). Injectable and morphine oral solid sustained release (SR) were the most available (59% and 55%). Methadone (oral) was the least expensive (Me=0.5) followed by fentanyl (transdermal; Me=2.2). The Me price for morphine oral solid IR and ratios between dispensed and IBP were lower in HIC than in LMIC (price=0.03 vs. 0.16; ratio=2.23 vs. 0.03). Affordability for morphine oral solid IR was five days (Me=0.1; range=29-0.25).

CONCLUSION

Patients in LMIC and LIC have limited access to opioids, and there are subsidies in place for more expensive medications and formulations in all GNI levels, but not for morphine oral solid IR. Additional research is necessary to identify the reasons behind these findings.

A review of common methods to convert morphine to methadone

When dosed appropriately on carefully chosen patients, methadone can be a very safe and effective choice in managing chronic pain. Many authors have discussed important issues surrounding patient selection, drug interactions, screening for QTc prolongation and monitoring. This article will focus on the dosing dilemma that exists after the patient is deemed an appropriate candidate for methadone and a conversion is necessary from another opioid. Despite many publications dedicated to addressing this challenging topic, there is no consensus on the most appropriate method for converting an opioid regimen to methadone. Given the lack of concrete guidance, clinicians in a community setting are likely to be faced with an increased challenge if there are no available pain specialists to provide clinical support. Common methods for converting morphine to methadone will be reviewed and two clinical patient scenarios used to illustrate the outcomes of applying the methods.

Serum concentrations of opioids when comparing two switching strategies to methadone for cancer pain

PURPOSE

Our aim was to compare pharmacological aspects of two switching strategies from morphine/oxycodone to methadone; the stop and go (SAG) strategy in which methadone is started directly after the initial opioid has been stopped, and the 3-days switch (3DS), in which morphine/oxycodone is gradually changed to methadone by cross-tapering over 3 days.

METHODS

Forty-two cancer patients with pain and/or opioid side effects were assessed in this randomised trial. Trough serum concentrations of methadone, morphine, morphine-6-glucuronide (M6G), and oxycodone were measured on days 1, 2, 3, 4, 7, and 14. Primary outcome was number of patients with methadone concentrations in apparent C(SS) on day 4. Secondary outcomes were exposure to opioids during the first 3 days, interindividual variation of opioid concentrations, and correlation between methadone concentrations and pain intensity (PI) day 3.

RESULTS

Thirty-five patients received methadone (16 in the SAG group, 19 in the 3DS group). The median preswitch morphine equivalent doses were 620 (range 350-2000) mg/day in the SAG group and 800 (range 90-3600) mg/day in the 3DS group (p = 0.43);42% reached C(SS) for methadone in the SAG group on day 4 compared with 22% in the 3DS group (p = 0.42). The SAG group was significantly less exposed to morphine/M6G/oxycodone and significantly more exposed to methadone in the first 3 days. Methadone showed a low correlation with PI. More patients dropped out after intervention in the SAG group than in the 3DS group (38% vs. 5%; p = 0.032). One SAG patient suffered from respiratory depression on day 5.

CONCLUSION

The SAG group was initially more exposed to methadone and less to the replaced opioids but without observed clinical benefit and with a higher dropout rate. Patients switched to methadone should be followed closely for the first 5 days, regardless of switching strategy.

How to switch from morphine or oxycodone to methadone in cancer patients? a randomised clinical phase II trial

AIM

Opioid switching is a treatment strategy in cancer patients with unacceptable pain and/or adverse effects (AEs). We investigated whether patients switched to methadone by the stop and go (SAG) strategy have lower pain intensity (PI) than the patients switched over three days (3DS), and whether the SAG strategy is as safe as the 3DS strategy.

METHODS

In this prospective, open, parallel-group, multicentre study, 42 cancer patients on morphine or oxycodone were randomised to the SAG or 3DS switching-strategy to methadone. The methadone dose was calculated using a dose-dependent ratio. PI, AEs and serious adverse events (SAEs) were recorded daily for 14 days. Primary outcome was average PI day 3. Secondary outcomes were PI now and AEs day 3 and 14 and number of SAEs.

RESULTS

Twenty one patients were randomised to each group, 16 (SAG) and 19 (3DS) patients received methadone. The mean preswitch morphine doses were 900 mg/day in SAG and 1330 mg/day in 3DS. No differences between groups were found in mean average PI day 3 (mean difference 0.5 (CI -1.2-2.2); SAG 4.1 (CI 2.3-5.9) and 3DS 3.6 (CI 2.9-4.3) or in PI now. The SAG group had more dropouts and three SAEs (two deaths and one severe sedation). No SAEs were observed in the 3DS group.

CONCLUSION

The SAG patients reported a trend of more pain, had significantly more dropouts and three SAEs, which indicate that the SAG strategy should not replace the 3DS when switching from high doses of morphine or oxycodone to methadone.

Morphine to Methadone Conversion: An Interpretation of Published Data

For the past 20 years, methadone has been experiencing resurgence in the palliative care community as a second-line opioid for the treatment of cancer pain. The advantages of using methadone for refractory pain in patients with cancer or in those who could not tolerate the side effects of other opioids such as morphine are well cited in recent literature. Advantages of methadone over other opioids include dual elimination without active metabolites, allowing safe use with renal and liver failure, N-methyl-D-aspartate (NMDA) and delta receptor activity in addition to mu receptor agonism, multiple routes of administration, rapid onset of action, long half-life, low cost, and fewer adverse effects. Despite the abundance of recent case reports and literature reviews demonstrating the effective use of methadone in patients with cancer, there is a lack of consensus for an appropriate method for converting morphine (and by extension, other opioids) to methadone. This article will review methadone pharmacology and multiple proposed conversion methods; a case report illustrating a popular method for high-dose conversion is also included.

Myoclonus associated with high-dose parenteral methadone

Methadone is generally believed to be devoid of neuroexcitatory properties, and its use is increasing. This paper reports two cases of myoclonus with high-dose parenteral methadone in patients with cancer under hospice care. This side effect may be dose related and/or due to the parenteral route of administration. Reduction of the dose and change of route was sufficient to eliminate the myoclonus while maintaining an adequate pain control. Possible mechanisms for methadone causing myoclonus include a redistribution of receptor saturation in the N-methyl-D-aspartate (NMDA) and delta receptors. Ketamine may be an option for patients with intractable pain who develop methadone-induced myoclonus.

Consensus guideline on parenteral methadone use in pain and palliative care

Once used only as third-line therapy for chronic pain management, methadone is now being used as first- and second-line therapy in palliative care. The risks and stigma associated with methadone use are known, but difficulties with dosing methadone and lack of an established conversion protocol from other opiates have limited the access for patient populations who could potentially benefit from this medication. For palliative care patients, the benefits of methadone can far outweigh its risks. This article provides an overview and specific recommendations on the use of parenteral methadone in pain and palliative care, with a focus on the transition from hospital to home/hospice care. The goal of this consensus guideline is to assist clinicians who are providing chronic pain management in acute care hospital and nonhospital settings (i.e., hospice, long-term care facilities, and community) for patients with life-limiting illnesses, where the goals of care are focused on comfort (i.e., palliative care). The recommendations in this article intend to promote a standard of care involving the use of intravenous methadone with the aim of reaching a broader population of patients for whom this drug would provide important benefits.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 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 neurological 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).