A comparative study of the efficacy and pharmacokinetics of oral methadone and morphine in the treatment of severe pain in patients with cancer

[Pharmacological pain management in cancer patients]

Pharmacological pain therapy in cancer patients is based on guideline recommendations, which, however, do not fully coincide in all aspects due to varying weighting of evidence. The present article discusses current issues including the decreasing significance of the World Health Organization (WHO) analgesic ladder, with its distinction between step 2 and 3 being increasingly questioned. Risks of nonopioid analgesics such as paracetamol and nonsteroidal anti-inflammatory drugs (NSAIDs), particularly in older populations, are discussed. Paracetamol may potentially reduce the effectiveness of immunotherapies. Aspects of administering analgesics via a feeding tube are considered. Recommendations for the treatment of episodic pain, transitioning between different opioids, and some relevant interactions are also discussed.

Drug-Drug Interaction Studies of Esmethadone (REL-1017) Involving CYP3A4- and CYP2D6-Mediated Metabolism

BACKGROUND AND OBJECTIVE

Esmethadone (dextromethadone; d-methadone; S-methadone (+)-methadone; REL-1017) is the opioid inactive dextro-isomer of racemic methadone. Esmethadone is a low potency N-methyl-D-aspartate (NMDA) receptor channel blocker with higher affinity for GluN2D subtypes. Esmethadone showed robust, rapid, and sustained antidepressant effects in patients with major depressive disorder (MDD) with inadequate response to ongoing serotonergic antidepressant treatment.

METHODS

Here we described the results of in vitro and phase 1 clinical trials aimed at investigating the esmethadone metabolism and possible drug-drug interactions.

RESULTS

Esmethadone is primarily metabolized to EDDP (2-ethylene-1,5-dimethyl-3,3-diphenylpyrrolidine) by multiple enzymes, including CYP3A4/5 and CYP2B6. In vitro studies showed that esmethadone inhibits CYP2D6 with IC50 of 9.6 μM and is an inducer of CYP3A4/5. The clinical relevance of the inhibition of CYP2D6 and the induction of CYP3A4 were investigated by co-administering esmethadone and dextromethorphan (a substrate for CYP2D6) or midazolam (a substrate for CYP3A4) in healthy volunteers. The administration of esmethadone at the dosage of 75 mg (which is the loading dose administered to patients in MDD clinical trials) significantly increased the exposure (AUC) of both dextromethorphan and its metabolite dextrorphan by 2.71 and 3.11-fold, respectively. Esmethadone did not modify the pharmacokinetic profile of midazolam, while it increased Cmax and AUC of its metabolite 1'-hydroxymidazolam by 2.4- and 3.8-fold, respectively. A second study evaluated the effect of the CYP3A4 inhibitor cobicistat on the pharmacokinetics of esmethadone. Cobicistat slightly increase (+32%) the total exposure (AUC0-inf) of esmethadone.

CONCLUSIONS

In summary, esmethadone demonstrated a negligible effect on CYP3A4 induction and its metabolism was not meaningfully affected by strong CYP3A4 inhibitors while it increased exposure of CYP2D6-metabolized drugs.

Use of physiologically‐based pharmacokinetic modeling to inform dosing of the opioid analgesics fentanyl and methadone in children with obesity

Obesity is an increasingly alarming public health threat, with nearly 20% of children classified as obese in the United States today. Children with obesity are commonly prescribed the opioids fentanyl and methadone, and accurate dosing is critical to reducing the risk of serious adverse events associated with overexposure. However, pharmacokinetic studies in children with obesity are challenging to conduct, so there is limited information to guide fentanyl and methadone dosing in these children. To address this clinical knowledge gap, physiologically‐based pharmacokinetic models of fentanyl and methadone were developed in adults and scaled to children with and without obesity to explore the interplay of obesity, age, and pharmacogenomics. These models included key obesity‐induced changes in physiology and pharmacogenomic effects. Model predictions captured observed concentrations in children with obesity well, with an overall average fold error of 0.72 and 1.08 for fentanyl and methadone, respectively. Model simulations support a reduced fentanyl dose (1 vs. 2 μg/kg/h) starting at an earlier age (6 years) in virtual children with obesity, highlighting the importance of considering both age and obesity status when selecting an infusion rate most likely to achieve steady‐state concentrations within the target range. Methadone dosing simulations highlight the importance of considering genotype in addition to obesity status when possible, as cytochrome P450 (CYP)2B6*6/*6 virtual children with obesity required half the dose to match the exposure of wildtype children without obesity. This physiologically‐based pharmacokinetic modeling approach can be applied to explore dosing of other critical drugs in children with obesity.

Effect of Prenatal Opioid Exposure on the Human Placental Methylome

Prenatal exposure to addictive drugs can lead to placental epigenetic modifications, but a methylome-wide evaluation of placental DNA methylation changes after prenatal opioid exposure has not yet been performed. Placental tissue samples were collected at delivery from 19 opioid-exposed and 20 unexposed control full-term pregnancies. Placental DNA methylomes were profiled using the Illumina Infinium HumanMethylationEPIC BeadChip. Differentially methylated CpG sites associated with opioid exposure were identified with a linear model using the ‘limma’ R package. To identify differentially methylated regions (DMRs) spanning multiple CpG sites, the ‘DMRcate’ R package was used. The functions of genes mapped by differentially methylated CpG sites and DMRs were further annotated using Enrichr. Differentially methylated CpGs (n = 684, unadjusted p < 0.005 and |∆β| ≥ 0.05) were mapped to 258 genes (including PLD1, MGAM, and ALCS2). Differentially methylated regions (n = 199) were located in 174 genes (including KCNMA1). Enrichment analysis of the top differentially methylated CpG sites and regions indicated disrupted epigenetic regulation of genes involved in synaptic structure, chemical synaptic transmission, and nervous system development. Our findings imply that placental epigenetic changes due to prenatal opioid exposure could result in placental dysfunction, leading to abnormal fetal brain development and the symptoms of opioid withdrawal in neonates.

Methadone bioavailability and dose conversion implications with intravenous and enteral administration: A scoping review

PURPOSE

Despite its availability for more than 70 years, many details concerning methadone remain contentious, such as the dosing equivalents for intravenous and enteral administration. A scoping review was performed to evaluate whether existing literature on methadone bioavailability in human subjects support the current recommendation that an equivalent enteral dose is twice the intravenous dose.

METHODS

A librarian-assisted search of the PubMed and EMBASE databases identified all English-language articles with the terms methadone and bioavailability and/or conversion in the title or abstract published from inception though December 2019. A manual search of references was also performed to identify any additional articles. Studies were included in a scoping review if they were published in English and evaluated methadone bioavailability in human subjects.

RESULTS

Among 65 publications initially identified, 6 studies involving a total of 50 patients were included in the review. Bioavailability data for healthy volunteers and patients with opioid use disorder, metastatic cancer, chronic pain from malignant or nonmalignant disease were available for analysis. The pooled mean (95% confidence interval) bioavailability (F) was 85.4% (75.2%-95.6%), with heterogeneity (I2) of 0. In the 4 studies that provided individual patient-level data, F was >50% in 40 of 42 patient measurements (95.2%) and ≥75% in 33 of 42 patient measurements (78.6%).

CONCLUSION

Available evidence suggests the bioavailability of methadone is generally more than 75%, there is limited evidence for the currently recommended 1:2 ratio (intravenous:enteral), and a more appropriate dosing ratio may be 1:1.3. This scoping review underscores the need for further research to establish an effective and safe ratio when converting between intravenous and enteral dosing formulations of methadone.

Clinical pharmacology and dosing regimen optimization of neonatal opioid withdrawal syndrome treatments

In this paper, we review the management of neonatal opioid withdrawal syndrome (NOWS) and clinical pharmacology of primary treatment agents in NOWS, including morphine, methadone, buprenorphine, clonidine, and phenobarbital. Pharmacologic treatment strategies in NOWS have been mostly empirical, and heterogeneity in dosing regimens adds to the difficulty of extrapolating study results to broader patient populations. As population pharmacokinetics (PKs) of pharmacologic agents in NOWS become more well‐defined and knowledge of patient‐specific factors affecting treatment outcomes continue to accumulate, PK/pharmacodynamic modeling and simulation will be powerful tools to aid the design of optimal dosing regimens at the patient level. Although there is an increasing number of clinical trials on the comparative efficacy of treatment agents in NOWS, here, we also draw attention to the importance of optimizing the dosing regimen, which can be arguably equally important at identifying the optimal treatment agent.

Pharmacokinetics and pharmacodynamics of methadone administered intravenously and intramuscularly to isoflurane-anesthetized chickens

OBJECTIVE

To determine the pharmacokinetics and pharmacodynamics of methadone after IV or IM administration to isoflurane-anesthetized chickens.

ANIMALS

6 healthy adult Hy-Line hens.

PROCEDURES

In a randomized crossover-design study, methadone (6 mg/kg) was administered IV and IM to isoflurane-anesthetized chickens with a 1-week washout period between experiments. Blood samples were collected immediately before and at predetermined time points up to 480 minutes after methadone administration. Plasma concentrations were determined by liquid chromatography-mass spectrometry, and appropriate compartmental models were fit to the plasma concentration-versus-time data. Cardiorespiratory variables were compared between treatments and over time with mixed-effect repeated-measures analysis.

RESULTS

A 3-compartment model best described the changes in plasma methadone concentration after IV or IM administration. Estimated typical values for volumes of distribution were 692 mL/kg for the central compartment and 2,439 and 2,293 mL/kg for the first and second peripheral compartments, respectively, with metabolic clearance of 23.3 mL/kg/min and first and second distributional clearances of 556.4 and 51.8 mL/kg/min, respectively. Typical bioavailability after IM administration was 79%. Elimination half-life was 177 minutes, and maximum plasma concentration after IM administration was 950 ng/mL. Heart rate was mildly decreased at most time points beginning 5 minutes after IV or IM drug administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Disposition of methadone in isoflurane-anesthetized chickens was characterized by a large volume of distribution and moderate clearance, with high bioavailability after IM administration. Additional studies are warranted to assess pharmacokinetics and pharmacodynamics of methadone in awake chickens.

Switching Ratio from Parenteral to Oral Methadone 1:1.2 Is Safer Compared with Ratio 1:2 in Patients with Controlled Cancer Pain: A Multicenter Randomized-Controlled Trial (RATIOMTD-010810)

Background: The most commonly used switching ratio from parenteral to oral methadone is 1:2. Methadone is highly bioavailable and a lower ratio might result in similar analgesia with less toxicity. Objective: To compare success and side effects with two ratios from parenteral to oral methadone: 1:2 versus 1:1.2 in hospitalized patients with cancer pain. Design: A multicenter double-blind randomized clinical trial. Settings/Particiants: Inpatients with well-controlled cancer pain with parenteral methadone requiring rotation to the oral route. Measurements: Outcomes included pain intensity (Brief Inventory Pain), opioid toxicity (Common Toxicology Criteria for Adverse Events), and methadone dose. Success was defined as no toxicity with good pain control at 72 hours. Results: Thirty-nine of forty-four randomized patients were evaluable: 21 in ratio 1:2 and 18 in ratio 1:1.2. Seventy-one percent male. Median age 65 years. No significant differences in basal clinical characteristics between both groups. Median methadone dose pre/post switching was 24.5 mg ±13.5 and 49 mg ±27.3 for ratio 1:2, versus 23.3 mg ±9.4 (p: not significant) and 28 mg ±11.3 (p < 0.01) for ratio 1:1.2. Pain was well controlled without differences between both ratios. Drowsiness at day +1 (p < 0.017) and myoclonus at day +3 (p < 0.019) were more prevalent in group 1:2. Success was observed in 12 patients in ratio 1:2 versus 18 in ratio 1:1.2 (p < 0.001). Methadone side effects were observed in 12 patients in ratio 1:2 (mainly neurotoxicity symptoms) versus 2 in ratio 1:1.2 (p < 0.005). Conclusion: Ratio 1:1.2 when changing from parenteral to oral methadone resulted in lower toxicity and no difference in analgesia. More conservative dose adjustment during methadone route change should be considered. European Clinical Trials Register (EudraCT No. 2010-024092-39).

Magnesium Salt, a Simple Strategy to Improve Methadone Analgesia in Chronic Pain: An Isobolographic Preclinical Study in Neuropathic Mice

Analgesic efficacy of methadone in cancer and chronic non-cancer pains is greater than that of other opioids, probably because of its unique pharmacokinetics properties and also because it targets glutamatergic receptors in addition to µ-opioid receptors. However, methadone has drawbacks which are clearly related to dosing and treatment duration. The authors hypothesized that the antinociceptive efficacy of methadone could be synergistically potentiated by magnesium and copper salts in a preclinical mouse model of chronic pain, using the intraplantar formalin test as algesimetric tool. The spared nerve injury mice model was used to generate mononeuropathy. A low dose (0.25%) formalin was injected in the neuropathic limb in order to give rise only to Phase I response, resulting from direct activation by formalin of nociceptive primary afferents. Licking/biting of the formalin-injected limb was evaluated as nociceptive behavior during a 35-min observation period. Dose-response curves for intraperitoneal magnesium sulfate (10, 30, 100, and 300 mg/kg i.p.), copper sulfate (0.1, 0.3, 1, and 3 mg/kg i.p.) and methadone (0.1, 0.3, 1, and 3 mg/kg i.p.) allowed to combine them in equieffective doses and to determine their interaction by isobolographic analysis. Magnesium sulfate, copper sulfate and methadone dose-dependently decreased the nociceptive response evoked by formalin injection, the respective ED₅₀ being 76.38, 1.18, and 0.50 mg/kg i.p. Isobolographic analysis showed a superadditive interaction for magnesium and methadone. Indeed, despite that both ED₅₀ are obviously equieffective, the ED₅₀ for the MgSO4/methadone combination contained less than one third of the methadone having the ED₅₀ for methadone alone. For the CuSO₄/methadone combination, the interaction was only additive. Extrapolated to clinical settings, the results suggest that magnesium salts might be used to improve synergistically the efficacy of methadone in neuropathy, which would allow to reduce the dose of methadone and its associated side effects.

Corrected QT Interval Prolongation in Pediatric and Young Adult Patients on Methadone for Cancer-Related Pain

CONTEXT

Methadone has been reported to prolong the corrected QT (QTc) interval and increase the risk of torsades de pointes.

OBJECTIVES

Our study examined the frequency of QTc prolongation among pediatric and young adult patients starting methadone for cancer pain.

METHODS

All patients followed a standardized protocol. Electrocardiograms (ECGs) were obtained at baseline (methadone starting day to 14 days prior), 1-2 weeks, and 4-6 weeks later. QTc values were manually calculated using the Bazett formula. QTc prolongation was defined as ≥460 milliseconds (ms) for prepubertal children, ≥470 ms for pubertal males, and ≥480 ms for pubertal females.

RESULTS

Baseline ECGs were completed in 42 patients. Follow-up ECGs were completed in 38 of 42 (91%) and 31 of 42 (74%) patients at 1-2 weeks and 4-6 weeks, respectively. No patients had prolongation of the QTc at baseline, and 1 of 38 (3%) patients had a prolonged QTc at weeks 1-2. This patient had a history of prolonged QTc that the family did not initially report. No patients had prolongation of the QTc at weeks 4-6. No patients had torsades de pointes or ventricular fibrillation, and none died suddenly. Median (interquartile range [IQR]) baseline QTc was 391 (377-400) ms; median (IQR) 1-2 week follow-up QTc was 399 (374-411) ms (P = .05), and median (IQR) 4-6 week follow-up QTc was 393 (379-423) ms (P = .01).

CONCLUSION

Clinically significant prolongation of the QTc interval occurred only in one patient who had a history of prolonged QTc. Prolonged QTc is rare in this population.

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.

Opioids in cancer-related pain: current situation and outlook

PURPOSE

Despite progress in treatments, cancer pain remains underestimated, poorly assessed and under-treated. Prescribing strong opioids, because of their specificities, requires precision in management considering their pharmacology but also a clear understanding of recommendations. Some clinicians highlight the risk of addiction, excessive sedation and respiratory depression and their need for information. Our objective in this review is to suggest some clinical guidance for the positioning and daily use of opioids within cancer pain management.

METHODS

Critical reflection based on literature analysis and clinical practice.

RESULTS

Strong opioids may be initiated as soon as pain diagnosis is defined. Factors to consider are pain aetiology, opioid pharmacokinetics and pharmacodynamics, genetic polymorphism, physiology (age, gender, weight and pregnancy), comorbidities (especially renal, hepatic, cardiovascular diseases), chronobiology, environmental factors, medication interference and treatment adherence. Achieving the best-balanced opioid treatment for background pain is complex, mainly due to the variable benefit/risk ratio between individuals and the experience of breakthrough cancer pain. Opioid initiation alongside a dynamic reassessment of pain should be fully integrated into the patient's management to optimise analgesia. The efficacy and safety of a strong opioid treatment need to be re-evaluated and adapted to individuals constantly as it varies over time.

CONCLUSIONS

Cancer pain is multimorphic and permanently changing due to disease evolution, curative treatments and disruptive events (concomitant treatments, pain from associated disease, comorbidities and complications, modifications of the environment). Well-managed opioids are the cornerstone of a complex environment requiring multidisciplinary dynamic assessments integrated into the patient's care pathway.

Morphine infusor pump switch to oral methadone

Between 2014 and 2017, four patients with widespread cancer were referred to a home palliative care team from a hospital in Oviedo (Spain) with subcutaneous elastomeric infusion pump containing 180-260 mg/day of morphine for previously uncontrolled pain. 3-4 rotations were performed over 5-11 days, gradually substituting morphine for oral methadone (three times a day) to minimise the risks of rapid conversion, with a highly variable final subcutaneous morphine:oral methadone ratio (5:1 to 17:1), guided by the absence of pain, and to enhance the patient's functional capacity avoiding device dependence. The final methadone dose varied between 15 and 39 mg/day. There was daily telephone supervision and visits every 2-4 days. Patient demise occurred 56, 111, 168 and 350 days following the opioid conversion, and methadone was maintained until then. In all cases and prior to concluding the rotation, pain was controlled and sleepiness had subsided.

Attitudes, Beliefs, and Practices of Pediatric Palliative Care Physicians Regarding the Use of Methadone in Children With Advanced Cancer

CONTEXT

Methadone is a long-acting opioid known for its unique pharmacokinetic and pharmacodynamic properties. Most research on methadone in children is limited to its effect on the prolongation of the corrected QT (QTc) interval.

OBJECTIVES

To better understand the attitudes, beliefs, and practices of pediatric palliative care physicians regarding the use of methadone in children with advanced cancer.

METHODS

A survey was sent to the American Academy of Pediatrics Section of Hospice and Palliative Medicine LISTSERV. Information on demographics, dosing of methadone, and the use of electrocardiograms (ECGs) was collected.

RESULTS

One-hundred and five respondents (91%) provide palliative care to children ≥ 50% of the time, and a majority (81, 77%) prescribe methadone. Most (62, 77%) physicians were board certified in Hospice and Palliative Medicine, and most (39, 63%) certified via the direct pathway ("grandfathering"). Most physicians (57, 70%) do not use loading doses of methadone. Board-certified physicians trended toward decreasing methadone dose more (40% ± 19%) than non-board-certified physicians (28%, ±20%) when changing from the oral to intravenous route (P = 0.07). Respondents defined a QTc interval as "prolonged" (mean ± SD) at 444 milliseconds (±68 milliseconds). The percentage of patients receiving a baseline ECG was 65% (±33%). The most common reason for not performing a baseline ECG was that the patient was on hospice (13, 36%).

CONCLUSIONS

There are consistent practices, attitudes, and beliefs of pediatric palliative care providers with regard to methadone. More education is needed on the accurate value of a prolonged QTc interval.

Methadone for Pain Management in Children with Cancer

Methadone is a synthetic opioid with unique pharmacodynamic and pharmacokinetic properties. It is effective in treating both nociceptive and neuropathic pain, which commonly co-exist in children with cancer. Upon reviewing the literature describing the use of methadone in pediatric oncology patients, publications are limited in number and low in quality of evidence; nevertheless, there is support for the safety and efficacy of methadone in treating pain in children with cancer, particularly when pain is refractory to conventional treatment. Although the risk of life-threatening arrhythmia is commonly cited as an argument against the use of methadone, our review of the literature did not support this finding in children. Further evaluation with prospective studies is warranted to develop evidence-based recommendations for the use of methadone in pediatric oncology.

Fentanyl Sublingual Tablets Versus Subcutaneous Morphine for the Management of Severe Cancer Pain Episodes in Patients Receiving Opioid Treatment: A Double-Blind, Randomized, Noninferiority Trial

Purpose

Fentanyl sublingual tablets (FST) are a potentially useful alternative to parenteral opioids such as subcutaneous morphine (SCM) to treat severe cancer pain episodes. No direct comparison between FST and SCM is available. The aim of this study was to test noninferiority of FST versus SCM during the first 30 min postadministration.

Methods

Patients receiving stable opioid therapy and experiencing a severe pain episode were randomly assigned to either 100 µg FST or 5 mg SCM in a double-blind, double-dummy trial. Average pain intensity (PI) assessed on a 0 to 10 numerical rating scale at 10, 20, and 30 min postadministration was the main end point. Analysis of covariance, adjusted by baseline PI, was the main analysis. The noninferiority margin (NIm) for the between-group difference was set at −0.6, that is, equal to one third of the minimum clinically important PI difference of two points.

Results

A total of 114 patients were randomly assigned to either FST (n = 58) or SCM (n = 56). One patient (in the FST group) withdrew consent before drug administration and was excluded from analysis. Baseline mean PIs were 7.5 in both groups; mean average PIs assessed at 10, 20, and 30 min postadministration were 5.0 and 4.5 for FST and SCM, respectively, with the 95% CI of the between-group difference including the NIm (−0.49; 95% CI, −1.10 to 0.09). Patients taking FST received a second drug dose after 30 min more frequently than did patients taking SCM (51% v 37%, respectively; risk difference, −13%; 95% CI, −30% to 3%). Both treatments were well tolerated, with average follow-up adverse event scores below the response of “A Little.” Ninety-three percent of patients preferred the sublingual administration.

Conclusion

This trial did not show noninferiority of FST versus SCM within the chosen NIm. Both treatments were safe, and patients preferred the sublingual route of administration. FST provides analgesia with modest to moderate increased risk of lower efficacy compared with SCM.

Methadone for cancer pain

BACKGROUND

This is an updated review originally published in 2004 and first updated in 2007. This version includes substantial changes to bring it in line with current methodological requirements. Methadone is a synthetic opioid that presents some challenges in dose titration and is recognised to cause potentially fatal arrhythmias in some patients. It does have a place in therapy for people who cannot tolerate other opioids but should be initiated only by experienced practitioners. This review is one of a suite of reviews on opioids for cancer pain.

OBJECTIVES

To determine the effectiveness and tolerability of methadone as an analgesic in adults and children with cancer pain.

SEARCH METHODS

For this update we searched CENTRAL, MEDLINE, Embase, CINAHL, and clinicaltrials.gov, to May 2016, without language restriction. We also checked reference lists in relevant articles.

SELECTION CRITERIA

We sought randomised controlled trials comparing methadone (any formulation and by any route) with active or placebo comparators in people with cancer pain.

DATA COLLECTION AND ANALYSIS

All authors agreed on studies for inclusion. We retrieved full texts whenever there was any uncertainty about eligibility. One review author extracted data, which were checked by another review author. There were insufficient comparable data for meta-analysis. We extracted information on the effect of methadone on pain intensity or pain relief, the number or proportion of participants with 'no worse than mild pain'. We looked for data on withdrawal and adverse events. We looked specifically for information about adverse events relating to appetite, thirst, and somnolence. We assessed the evidence using GRADE and created a 'Summary of findings' table.

MAIN RESULTS

We revisited decisions made in the earlier version of this review and excluded five studies that were previously included. We identified one new study for this update. This review includes six studies with 388 participants. We did not identify any studies in children.The included studies differed so much in their methods and comparisons that no synthesis of results was feasible. Only one study (103 participants) specifically reported the number of participants with a given level of pain relief, in this case a reduction of at least 20% - similar in both the methadone and morphine groups. Using an outcome of 'no worse than mild pain', methadone was similar to morphine in effectiveness, and most participants who could tolerate methadone achieved 'no worse than mild pain'. Adverse event withdrawals with methadone were uncommon (12/202) and similar in other groups. Deaths were uncommon except in one study where the majority of participants died, irrespective of treatment group. For specific adverse events, somnolence was more common with methadone than with morphine, while dry mouth was more common with morphine than with methadone. None of the studies reported effects on appetite.We judged the quality of evidence to be low, downgraded due to risk of bias and sparse data. For specific adverse events, we considered the quality of evidence to be very low, downgraded due to risk of bias, sparse data, and indirectness, as surrogates for appetite, thirst and somnolence were used.There were no data on the use of methadone in children.

AUTHORS' CONCLUSIONS

Based on low-quality evidence, methadone is a drug that has similar analgesic benefits to morphine and has a role in the management of cancer pain in adults. Other opioids such as morphine and fentanyl are easier to manage but may be more expensive than methadone in many economies.

Opioid Conversions in Acute Care

Objective:

To discuss the historical basis and limitations of opioid conversion tables, review the relevant literature, and establish an evidence-based equianalgesic dose ratio (EDR) table for performing conversions in the acute care setting.

Data Sources:

Articles were identified through searches of MEDLINE (1966–January 2007) using the key words opioid, tolerance, conversion, dose, equianalgesic, equipotent, acute care, morphine, hydromorphone, fentanyl, methadone, and oxycodone. Additional references were located through a review of the bibliographies of articles cited and references cited in conversion tables.

Study Selection and Data Extraction:

All data sources identified were evaluated, and all information deemed relevant was included, with the exception of case series and case reports when higher level evidence was available.

Data Synthesis:

Opioid conversion tables are published in major textbooks, medical references, national guidelines, and review articles. Some conversion tables do not accurately reflect the dose ratios for which evidence is available. There is marginal evidence-based clinical data to support the dose ratios cited in these tables, particularly in the acute care setting where the clinical status of patients often changes rapidly. The barriers when performing route and opioid-to-opioid conversions in the acute care setting are formidable, but EDRs are provided, based on the best available evidence.

Conclusions:

In the acute care setting, calculation of dose ratios for opioids, based solely on opioid conversion tables, is an oversimplification of pain management, with a potential for adverse consequences. The calculation of EDRs is one step in an interdisciplinary process that must take into account patient- and institution-specific factors.

Methadone prolongs cardiac conduction in young patients with cancer-related pain

OBJECTIVE

Methadone prolongs cardiac conduction, from mild corrected QT (QTc) prolongation to torsades de pointes and ventricular fibrillation, in adults. However, methadone use for pain and its effects on cardiac conduction have not been investigated in pediatric populations.

METHODS

A retrospective review of QTc intervals in patients receiving methadone analgesia was conducted. Medical records from a 4-year period (September 2006 to October 2010) at a pediatric oncology institution were reviewed, and correlations were tested between cardiac conduction and methadone dosage and duration of therapy, electrolyte levels, renal and hepatic dysfunction, and concurrent medications.

RESULTS

Of the 61 patients who received methadone, 37 met our inclusion criteria and underwent 137 electrocardiograms (ECGs). During methadone treatment, the mean QTc was longer than that at baseline (446.5 vs 437.55 ms). The mean methadone dose was 27.0±24.3 mg/d (range, 5-125 mg/d; median, 20 mg/d) or 0.47±0.45 mg/kg per day (range, 0.05-2.25 mg/kg per day; median, 0.37 mg/kg per day), and the mean duration of therapy was 49 days. The authors identified a correlation between automated and manual ECG readings by two cardiologists (Pearson r=0.649; p<0.0001), but the authors found no correlations between methadone dose or duration and concurrent QTc-prolonging medications, sex, age, electrolyte abnormalities, or renal or hepatic dysfunction.

CONCLUSION

At a clinically effective analgesic dose, methadone dosage and duration were not correlated with QTc prolongation, even in the presence of other risk factors, suggesting that methadone use may be safe in pediatric populations. The correlation between automated and manual ECG readings suggests that automated ECG readings are reliable for monitoring cardiac conductivity during the reported methadone-dosage regimens.

Methadone as a Coanalgesic for Palliative Care Cancer Patients

BACKGROUND

Methadone offers many advantages for treating cancer pain. However, its pharmacokinetic profile makes its use as a full-dose opioid challenging.

OBJECTIVES

To evaluate the efficacy and safety of low-dose methadone as an adjunct to opioids in the treatment of cancer pain in palliative care patients.

DESIGN

A cohort was followed retrospectively for up to 60 days after the initiation of methadone as a coanalgesic.

SETTING/SUBJECTS

Patients were eligible if they were prescribed methadone as a coanalgesic for cancer pain management and followed by the palliative care team.

MEASUREMENTS

The primary efficacy end point was reduction of pain intensity (11-point numerical rating scale). Variables associated with pain intensity reduction were explored using logistic regressions. Adverse events were collected throughout the follow-up.

RESULTS

Seventy-two of the 146 subjects (49%) qualified as significant responders (≥30% reduction in pain intensity). Median time to significant response was seven days, and pain intensity on the day of methadone initiation predicted the response to treatment. The most frequently reported adverse events were drowsiness, confusion, constipation, and nausea. As expected in a palliative care population, there was a substantial amount of missing data.

CONCLUSIONS

A significant reduction in pain can be seen rapidly after the addition of methadone as a coanalgesic, particularly among patients with high pain intensity. More studies are needed to corroborate the efficacy of methadone as an adjunct to opioids.

Oral morphine for cancer pain

BACKGROUND

This is the third updated version of a Cochrane review first published in Issue 4, 2003 of The Cochrane Library and first updated in 2007. Morphine has been used for many years to relieve pain. Oral morphine in either immediate release or modified release form remains the analgesic of choice for moderate or severe cancer pain.

OBJECTIVES

To determine the efficacy of oral morphine in relieving cancer pain, and to assess the incidence and severity of adverse events.

SEARCH METHODS

We searched the following databases: Cochrane Central Register of Controlled Trials (CENTRAL 2015, Issue 9); MEDLINE (1966 to October 2015); and EMBASE (1974 to October 2015). We also searched ClinicalTrials.gov (1 October 2015).

SELECTION CRITERIA

Published randomised controlled trials (RCTs) using placebo or active comparators reporting on the analgesic effect of oral morphine in adults and children with cancer pain. We excluded trials with fewer than 10 participants.

DATA COLLECTION AND ANALYSIS

One review author extracted data, which were checked by another review author. There were insufficient comparable data for meta-analysis to be undertaken or to produce numbers needed to treat (NNTs) for the analgesic effect. We extracted any available data on the number or proportion of participants with 'no worse than mild pain' or treatment success (very satisfied, or very good or excellent on patient global impression scales).

MAIN RESULTS

We identified seven new studies in this update. We excluded six, and one study is ongoing so also not included in this update. This review contains a total of 62 included studies, with 4241 participants. Thirty-six studies used a cross-over design ranging from one to 15 days, with the greatest number (11) for seven days for each arm of the trial. Overall we judged the included studies to be at high risk of bias because the methods of randomisation and allocation concealment were poorly reported. The primary outcomes for this review were participant-reported pain and pain relief.Fifteen studies compared oral morphine modified release (Mm/r) preparations with morphine immediate release (MIR). Fourteen studies compared Mm/r in different strengths; six of these included 24-hour modified release products. Fifteen studies compared Mm/r with other opioids. Six studies compared MIR with other opioids. Two studies compared oral Mm/r with rectal Mm/r. Three studies compared MIR with MIR by a different route of administration. Two studies compared Mm/r with Mm/r at different times and two compared MIR with MIR given at a different time. One study was found comparing each of the following: Mm/r tablet with Mm/r suspension; Mm/r with non-opioids; MIR with non-opioids; and oral morphine with epidural morphine.In the previous update, a standard of 'no worse than mild pain' was set, equivalent to a score of 30/100 mm or less on a visual analogue pain intensity scale (VAS), or the equivalent in other pain scales. Eighteen studies achieved this level of pain relief on average, and no study reported that good levels of pain relief were not attained. Where results were reported for individual participants in 17 studies, 'no worse than mild pain' was achieved by 96% of participants (362/377), and an outcome equivalent to treatment success in 63% (400/638).Morphine is an effective analgesic for cancer pain. Pain relief did not differ between Mm/r and MIR. Modified release versions of morphine were effective for 12- or 24-hour dosing depending on the formulation. Daily doses in studies ranged from 25 mg to 2000 mg with an average of between 100 mg and 250 mg. Dose titration was undertaken with both instant release and modified release products. A small number of participants did not achieve adequate analgesia with morphine. Adverse events were common, predictable, and approximately 6% of participants discontinued treatment with morphine because of intolerable adverse events.The quality of the evidence is generally poor. Studies are old, often small, and were largely carried out for registration purposes and therefore were only designed to show equivalence between different formulations.

AUTHORS' CONCLUSIONS

The conclusions have not changed for this update. The effectiveness of oral morphine has stood the test of time, but the randomised trial literature for morphine is small given the importance of this medicine. Most trials recruited fewer than 100 participants and did not provide appropriate data for meta-analysis. Only a few reported how many people had good pain relief, but where it was reported, over 90% had no worse than mild pain within a reasonably short time period. The review demonstrates the wide dose range of morphine used in studies, and that a small percentage of participants are unable to tolerate oral morphine. The review also shows the wide range of study designs, and inconsistency in cross-over designs. Trial design was frequently based on titration of morphine or comparator to achieve adequate analgesia, then crossing participants over in cross-over design studies. It was not clear if these trials were sufficiently powered to detect any clinical differences between formulations or comparator drugs. New studies added to the review for the previous update reinforced the view that it is possible to use modified release morphine to titrate to analgesic effect. There is qualitative evidence that oral morphine has much the same efficacy as other available opioids.

Methadone analgesia in the critically ill

PURPOSE

Methadone is increasingly used as an analgesic or a bridge to weaning other analgesics and sedatives in critically ill patients. This review discusses the pharmacology of methadone, summarizes available evidence for its use in the intensive care unit setting, and makes suggestions for appropriate use and monitoring.

MATERIALS/METHODS

Articles evaluating the efficacy, safety, and pharmacology of methadone were identified from a PubMed search through June 2015. References from selected articles were reviewed for additional material. Experimental and observational English-language studies that focused on the efficacy, safety, and pharmacology of methadone in critically-ill adults and children were selected.

RESULTS

Methadone is a synthetic opioid analgesic with potential advantages over other commonly used opioids. Limited evidence from critically ill pediatric, adult, and burn populations suggests that methadone protocols may expedite weaning opiate infusions, decrease the length of mechanical ventilation, and reduce the incidence of negative outcomes such as opiate withdrawal, delirium, and over-sedation.

CONCLUSIONS

Data from current literature supports a role for methadone analgesia in weaning opiates and potentially reducing the duration of mechanical ventilation in critically ill patients. More studies are needed to confirm these benefits and determine criteria for patient selection.

Methods of Rotation From Another Strong Opioid to Methadone for the Management of Cancer Pain: A Systematic Review of the Available Evidence

CONTEXT

Up to 44% of patients with cancer-related pain require opioid rotation (OR) because of inadequate analgesia or side effects. No consensus exists regarding the most efficacious method for rotation to methadone.

OBJECTIVES

To define the available evidence regarding methods of rotation to methadone and to determine if sufficient evidence exists regarding the superiority of one method.

METHODS

A predefined search strategy, using Medical Subject Headings (MeSH) search terms and keywords combined using Boolean operators, was performed. Study selection was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidance. Data were extracted, quality of studies assessed, and narrative synthesis undertaken.

RESULTS

A total of 3214 potentially relevant studies were identified. Twenty-five studies were included: 15 retrospective and 10 prospective (n = 1229). One trial compared three-day switch (3DS) and rapid conversion (RC) methods; two, 3DS; 10, RC; nine, ad libitum (AL). Success rates were as follows: 3DS-93%, RC-71.7%, and AL-92.8%. The single clinical trial and retrospective studies demonstrated poorer analgesia and an excess of adverse events (AEs) in the RC group (five dropouts because of AEs) compared with the 3DS group (no severe AEs). Time to stable analgesia was as follows: RC <4.3 days and AL <6 days.

CONCLUSION

Evidence identified was mainly from uncontrolled observational studies, making causality difficult to establish. Studies were heterogeneous in methodology and outcome measures. There was a trend toward excess AEs using the RC method, in comparison to the AL and 3DS methods. The methodological quality of the AL studies was low. A direct comparison of AL and 3DS methods would be informative.

The importance of catastrophizing for successful pharmacological treatment of peripheral neuropathic pain

Objective

Catastrophizing may be a negative predictor of pain-related outcomes. We evaluated the impact of catastrophizing upon success of first-line pharmacotherapy in the management of neuropathic pain (NeP) due to peripheral polyneuropathy.

Methods

Patients with confirmed NeP with NeP Visual Analog Scale (VAS) pain severity score ≥4 (0–10 scale) completed the Coping Strategies Questionnaire (CSQ) catastrophizing subscale at baseline. Pharmacological therapy consisting of first-line agents gabapentin, pregabalin, or a tricyclic antidepressant was initiated. Other measures examined included the Karnofsky Performance Scale, Beck Depression Inventory, EuroQol Quality of Life Health Questionnaire, and Modified Brief Pain Inventory. At 3 and 6 months, questionnaires were repeated and adverse effect reporting was completed. Outcome measures assessed were pharmacotherapy success (≥30% relief of NeP) and tolerability over 6 months of follow-up. Bivariate relationships using Pearson product-moment correlations were examined for baseline CSQ catastrophizing subscale score and the change in the NeP VAS scores and medication discontinuation.

Results

Sixty-six patients were screened, 62 subjects participated, and 58 subjects (94%) completed the final follow-up visit. Greater catastrophizing was associated with poor pain relief response and greater likelihood of discontinuation of pharmacotherapy, reports of greater disability, and impaired quality of life. Duration of pain was negatively associated with likelihood of pharmacotherapy success.

Conclusion

Catastrophizing exerts maladaptive effects on outcomes with pharmacotherapy in NeP patients. Detection of catastrophizing during clinical visits when pharmacological therapy is being considered can be a predictive factor for patient outcomes.

[Use of methadone in the elderly with cancer pain: a systematic review]

OBJECTIVE

To identify the clinical use of methadone as an analgesic in the management of cancer pain in elderly patients.

MATERIAL AND METHODS

We performed a systemic review of the literature on the specific use of methadone in elderly with cancer pain in MEDLINE, COCHRANE DATABASE and SCOPUS. A second search was conducted in MEDLINE to look for clinical trials and systematic review of the use of methadone in cancer pain, selecting only those in which the mean age of patients was ≥ 65 years old.

RESULTS

Four articles were obtained in the first search, and from the second 7 clinical trials, none of them specific to methadone use in elderly patients with cancer.

CONCLUSIONS

There are insufficient data on the use of methadone as an analgesic in the elderly with cancer. Given its pharmacological characteristics it must be used by trained personnel. Several recommendations are proposed for its use as an analgesic in the treatment of cancer pain in the elderly.

Oral morphine for cancer pain

BACKGROUND

This is the second updated version of a Cochrane review first published in Issue 4, 2003 of The Cochrane Library and first updated in 2007. Morphine has been used for many years to relieve pain. Oral morphine in either immediate release or modified release form remains the analgesic of choice for moderate or severe cancer pain.

OBJECTIVES

To determine the efficacy of oral morphine in relieving cancer pain, and assess the incidence and severity of adverse effects.

SEARCH METHODS

We searched the following databases: Cochrane Pain, Palliative and Supportive Care Group Trials Register (June 2013); Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2013, Issue 5, May); MEDLINE (1966 to June 2013); and EMBASE (1974 to June 2013).

SELECTION CRITERIA

Published randomised controlled trials (RCTs) using placebo or active comparators reporting on the analgesic effect of oral morphine in adults and children with cancer pain. Trials with fewer than ten participants were excluded.

DATA COLLECTION AND ANALYSIS

One review author extracted data, which were checked by another review author. There were insufficient comparable data for meta-analysis to be undertaken or to produce numbers needed to treat (NNTs) for the analgesic effect. We extracted any available data on the number or proportion of participants with 'no worse than mild pain' or treatment success (very satisfied, or very good or excellent on patient global impression scales).

MAIN RESULTS

Ten new studies (638 participants) were identified for this update, bringing the total of included studies to 62, with 4241 participants. Thirty-six studies used a cross-over design ranging from one to 15 days, with the greatest number (11) for seven days for each arm of the trial.Fifteen studies compared oral morphine modified release (Mm/r) preparations with morphine immediate release (MIR). Fourteen studies compared Mm/r in different strengths; six of these included 24-hour modified release products. Fifteen studies compared Mm/r with other opioids. Six studies compared MIR with other opioids. Two studies compared oral Mm/r with rectal Mm/r. Three studies compared MIR with MIR by a different route of administration. Two studies compared Mm/r with Mm/r at different times and two compared MIR with MIR given at a different time. One study was found comparing each of the following: Mm/r tablet with Mm/r suspension; Mm/r with non-opioids; MIR with non-opioids; and oral morphine with epidural morphine.In this update a standard of 'no worse than mild pain' was set equivalent to a score of 30/100 mm or less on a visual analogue pain intensity scale (VAS), or the equivalent in other pain scales. Eighteen studies achieved this level of pain relief on average, and no study reported that good levels of pain relief were not attained. Where results were reported for individual participants in 17 studies, 'no worse than mild pain' was achieved by 96% of participants (362/377), and an outcome equivalent to treatment success in 63% (400/638).Morphine is an effective analgesic for cancer pain. Pain relief did not differ between Mm/r and MIR. Modified release versions of morphine were effective for 12- or 24-hour dosing depending on the formulation. Daily doses in studies ranged from 25 mg to 2000 mg with an average of between 100 mg and 250 mg. Dose titration was undertaken with both instant release and modified release products. A small number of participants did not achieve adequate analgesia with morphine. Adverse effects were common and approximately 6% of participants discontinued treatment because of intolerable adverse effects.

AUTHORS' CONCLUSIONS

The effectiveness of oral morphine has stood the test of time, but the randomised trial literature for morphine is small given the importance of this medicine. Most trials recruited fewer than 100 participants and did not provide appropriate data for meta-analysis. Only a few reported how many people had good pain relief, but where it was reported, over 90% had no worse than mild pain within a reasonably short time period. The review demonstrates the wide dose range of morphine used in studies, and that a small percentage of participants are unable to tolerate oral morphine. The review also shows the wide range of study designs, and inconsistency in cross-over designs. Trial design was frequently based on titration of morphine or comparator to achieve adequate analgesia, then crossing participants over in cross-over design studies. It was not clear if these trials are sufficiently powered to detect any clinical differences between formulations or comparator drugs. New studies added to the review reinforce the view that it is possible to use modified release morphine to titrate to analgesic effect. There is qualitative evidence that oral morphine has much the same efficacy as other available opioids.

Methadone in post-herpetic neuralgia: A pilot proof-of-concept study

OBJECTIVE

This research was designed as a pilot proof-of-concept study to evaluate the use of low-dose methadone in post-herpetic neuralgia patients who remained refractory after first and second line post-herpetic neuralgia treatments and had indications for adding an opioid agent to their current drug regimens.

METHODS

This cross-over study was double blind and placebo controlled. Ten opioid naïve post-herpetic neuralgia patients received either methadone (5 mg bid) or placebo for three weeks, followed by a 15-day washout period and a second three-week treatment with either methadone or placebo, accordingly. Clinical evaluations were performed four times (before and after each three-week treatment period). The evaluations included the visual analogue scale, verbal category scale, daily activities scale, McGill pain questionnaire, adverse events profile, and evoked pain assessment. All patients provided written informed consent before being included in the study. ClinicalTrials.gov: NCT01752699 RESULTS: Methadone, when compared to placebo, did not significantly affect the intensity of spontaneous pain, as measured by the visual analogue scale. The intensity of spontaneous pain was significantly decreased after the methadone treatment compared to placebo on the category verbal scale (50% improved after the methadone treatment, none after the placebo, p=0.031). Evoked pain was reduced under methadone compared to placebo (50% improved after the methadone treatment, none after the placebo, p=0.031). Allodynia reduction correlated with sleep improvement (r=0.67, p=0.030) during the methadone treatment. The side effects profile was similar between both treatments.

CONCLUSIONS

Methadone seems to be safe and efficacious in post-herpetic neuralgia. It should be tried as an adjunctive treatment for post-herpetic neuralgia in larger prospective studies.

Use of opioid analgesics in the treatment of cancer pain: evidence-based recommendations from the EAPC

Here we provide the updated version of the guidelines of the European Association for Palliative Care (EAPC) on the use of opioids for the treatment of cancer pain. The update was undertaken by the European Palliative Care Research Collaborative. Previous EAPC guidelines were reviewed and compared with other currently available guidelines, and consensus recommendations were created by formal international expert panel. The content of the guidelines was defined according to several topics, each of which was assigned to collaborators who developed systematic literature reviews with a common methodology. The recommendations were developed by a writing committee that combined the evidence derived from the systematic reviews with the panellists' evaluations in a co-authored process, and were endorsed by the EAPC Board of Directors. The guidelines are presented as a list of 16 evidence-based recommendations developed according to the Grading of Recommendations Assessment, Development and Evaluation system.

Methadone use in children and young adults at a cancer center: a retrospective study

OBJECTIVE

To augment the literature on methadone applications in pediatric oncology, the authors reviewed the use of methadone at a pediatric cancer center over a 5-year period.

DESIGN AND SETTING

Forty-one patients received methadone for inpatient or outpatient pain management. The authors retrospectively reviewed their demographic characteristics, diagnoses, type of pain (nociceptive, neuropathic, or mixed) and causes of pain, and the indications, dose regimens, adverse effects, and outcomes of methadone treatment.

RESULTS

There were four types of clinical uses for methadone in 41 patients (10 patients had two): nociceptive pain unresponsive to other opioids (17 patients, 33.3 percent), neuropathic pain (20 patients, 39.2 percent), facilitation of weaning from opioids (11 patients, 21.6 percent), and end-of-life pain management (3 patients, 5.9 percent). The mean age of the 24 males (58.5 percent) and 17 females (41.5 percent) at the start of treatment was 15.7 years (range, 0.6-23 years). The most common diagnoses were leukemia (n = 10, 24.4 percent), osteosarcoma (n = 7, 17.0 percent), and rhabdomyosarcoma (n = 5, 12.2 percent). The causes of pain were bone marrow transplant (n = 13, 31.7 percent), amputation (n = 6, 14.6 percent), chemotherapy (n = 5, 12.2 percent), tumor (n = 5, 12.2 percent), limb-sparing surgery (n = 4, 9.8 percent), and other (n = 8, 19.5 percent). Efficacy was assessed at the end (or after 6 months) of methadone treatment. For many patients (43.1 percent), methadone showed efficacy in achieving the purpose for which it was prescribed, including reduction of nociceptive or neuropathic pain and prevention of opioid withdrawal. Sedation was the most common side effect (24.4 percent).

CONCLUSIONS

Methadone was effective for pediatric patients with neuropathic pain or nociceptive pain unresponsive to other opioids, and it effectively prevented opioid withdrawal.

Rational opioid dosing in the elderly: dose and dosing interval when initiating opioid therapy

Opioids are the mainstay of treatment for moderate to severe pain. However, opioid therapy in the elderly is often associated with significant morbidity because of excessive ventilatory depression. The large amount of interindividual variability in opioid dose-response relationships makes it difficult to individualize the dose and dosing interval to provide safe and effective analgesia. By examining how aging affects the pharmacokinetics (PK) and pharmacodynamics (PD) of opioids, it is possible to provide a rational basis for age adjustment in opioid dosing.

Characterization of the antinociceptive effects of the individual isomers of methadone after acute and chronic administrations

Methadone is a long-acting opioid used in the treatment of various pain states and substitution therapy in heroin addiction. Extensive behavioral characterization has been carried out using the racemate, but limited investigation has been performed with the individual isomers. The L-isomer is a potent opioid agonist, whereas the D-isomer has weak µ-opioid activity and has also been shown to possess N-methyl-D-aspartate antagonist properties in vitro. The acute antinociceptive effects of the isomers were evaluated in rats using a warm-water, tail-withdrawal procedure at two stimulus intensities (50° and 55°C). Increasing dose ratios of D-methadone to L-methadone were administered chronically to determine the ability of the D-isomer to modulate antinociceptive tolerance to the L-isomer. Acutely, both L-methadone (0.1-5.6 mg/kg, subcutaneously) and D-methadone (3.0-56.0 mg/kg, subcutaneously) produced antinociception, although the efficacy of the D-isomer was limited at 55°C. These effects were dose dependently blocked by naltrexone (0.01-1.0 mg/kg, subcutaneously). Administered chronically, D-methadone (1.7-10 mg/kg, subcutaneously) dose dependently blocked tolerance development to the L-isomer (1.7 mg/kg, subcutaneously). These findings support the antinociceptive effects of the isomers being opioid receptor mediated with the L-isomer functioning as a full-efficacy agonist, whereas the D-isomer seems to have lower efficacy. The ability of nonracemic doses of the D-isomer to prevent tolerance development to the L-isomer may be attributed to partial µ-agonist activity; however, N-methyl-D-aspartate antagonist activity cannot be discounted.

Is oral morphine still the first choice opioid for moderate to severe cancer pain? A systematic review within the European Palliative Care Research Collaborative guidelines project

The aim of this systematic review was to evaluate the evidence that oral morphine can be recommended as the first choice opioid in the treatment of moderate to severe cancer pain in updating the European Association for Palliative Care opioid recommendations. A systematic literature review was performed to update the 2007 Cochrane review 'Oral morphine for cancer pain'. The literature search was conducted on MedLine, EMBASE and Cochrane Central Register of Controlled Trials databases. The search strategy, limited in time (from 1 July 2006 to 31 October 2009), was aimed to be as extensive as possible using both text words and MeSH/EMTREE terms; a hand search of the reference lists of identified papers was also performed. Randomized clinical trials, containing data on efficacy and/or side effects of morphine, were identified. Among the papers retrieved from the cited databases and the Cochrane review, 17 eligible studies, for a total of 2053 patients, and a meta-analysis were selected. These studies do not add significant information to the previous Cochrane review confirming the limitation of efficacy and tolerability data on opioid-naïve and non-selected populations of cancer patients treated with morphine and suggesting that oral morphine, oxycodone and hydromorphone have similar efficacy and toxicity in this patient population.

Is oral methadone better than placebo or other oral/transdermal opioids in the management of pain?

AIM

To address the question: is oral methadone better than placebo, or other oral/transdermal opioids in the management of cancer pain?

METHOD

A literature search was performed to identify relevant studies. Search strategies included: (1) methadone (title) AND placebo (title or abstract) AND pain (title or abstract); (2) methadone (title) AND randomized (title or abstract) AND pain (title or abstract) AND cancer (title or abstract). Papers were reviewed for relevance to first-line opioid therapy.

RESULTS

No studies were identified comparing methadone to placebo for cancer pain. A single study compared methadone to placebo for neuropathic pain and demonstrated evidence of analgesic effect at a dose of 20 mg/day but not at a dose of 10 mg/day. Four studies compared oral methadone to either oral morphine, or oral morphine and transdermal fentanyl in a first-line setting: Gourlay 1986 (N = 18), Ventafridda 1986 (N =54), Bruera 2004 (N = 106) and Mercadante 2008 (N = 108). All studies demonstrated comparable, but not superior, analgesia with, overall, a comparable adverse effect profile. The duration of the study period for the three largest studies was 28 days. Two of these studies, Ventafridda 1986 and Mercadante 2008, indicated that, over time, the opioid escalation index was lower for methadone than for morphine. One study that used a 2:1 dose ratio between morphine and methadone was associated with a high attrition rate in the first week because of excessive sedation. This effect was not seen in the study that used a 4:1 morphine to methadone dose ratio with dose titration.

CONCLUSION

This limited data suggests that (1) methadone may be an equally effective candidate for first-line opioid therapy, (2) that it is possibly less expensive, (3) that there may be a propensity to sedation and dose accumulation unless there is close monitoring and conservative dose selection and (4) that it should be initiated with a calculated dose based on a morphine to methadone dose ratio of not less than 4:1.

Influences on the pharmacokinetics of oxycodone: a multicentre cross-sectional study in 439 adult cancer patients

Objective

Oxycodone is widely used for the treatment of cancer pain, but little is known of its pharmacokinetics in cancer pain patients. The aim of this study was to explore the relationships between ordinary patient characteristics and serum concentrations of oxycodone and the ratios noroxycodone or oxymorphone/oxycodone in cancer patients.

Methods

Four hundred and thirty-nine patients using oral oxycodone for cancer pain were included. The patients’ characteristics (sex, age, body mass index [BMI], Karnofsky performance status, “time since starting opioids”, “oxycodone total daily dose”, “time from last oxycodone dose”, use of CYP3A4 inducer/inhibitor, “use of systemic steroids”, “number of medications taken in the last 24 h”, glomerular filtration rate (GFR) and albumin serum concentrations) influence on oxycodone serum concentrations or metabolite/oxycodone ratios were explored by multiple regression analyses.

Results

Sex, CYP3A4 inducers/inhibitors, total daily dose, and “time from last oxycodone dose” predicted oxycodone concentrations. CYP3A4 inducers, total daily dose, and “number of medications taken in the last 24 h” predicted the oxymorphone/oxycodone ratio. Total daily dose, “time from last dose to blood sample”, albumin, sex, CYP3A4 inducers/inhibitors, steroids, BMI and GFR predicted the noroxycodone/oxycodone ratio.

Conclusion

Women had lower oxycodone serum concentrations than men. CYP3A4 inducers/inhibitors should be used with caution as these are predicted to have a significant impact on oxycodone pharmacokinetics. Other characteristics explained only minor parts of the variability of the outcomes.

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.

High dose versus moderate dose methadone maintenance: is there a better outcome?

Methadone dosing has been an issue of controversy among clinicians for a long time. Few recent studies reported that doses above 100 mg daily seem promising in better control of illicit opiate use for some patients, but more research is needed to support that notion. A retrospective chart review for patients maintained on methadone at Atlanta Veterans Affairs Medical Center was conducted. Patients were categorized into two groups: patients on a methadone dose of 60 to 100 mg daily (n = 34) and patients on a methadone dose greater than 100 mg daily (n = 25). Those charts were compared for urine drug screens for opiates and cocaine (first four from admission and most recent four screens), retention or drop out from the program, and Addiction Severity Index (ASI) composite score at admission and most recent score. The results of the first and last four urine drug screens for opiates showed that the moderate dose group was positive 23% and 17%, respectively. However, the high dose group was positive 14% and 8%, respectively. These results showed statistical significance (Chi-Square = 8.04, df = 3 and p =.03). ASI scores for drugs did not show statistically significant improvement for the moderate dose group (p =.19) but showed statistically significant improvement for the high dose group (p =.0002) when the result of the first and last ASI scores among each group were compared. The ASI scores for family problems showed statistically significant improvement for the moderate dose group (p =.03). High doses of methadone greater than 100 mg daily may provide a better outcome for illicit opiate use among some patients who would not respond to moderate doses.

Effect of P-glycoprotein inhibition on methadone analgesia and brain distribution in the rat

Methadone is an opiate drug that has been identified as an in-vitro substrate of the efflux pump P-glycoprotein (P-gp), active in the intestinal epithelium and in the blood–brain barrier (BBB), among other sites. The objective of this study was to test in vivo, in the rat model, the role of P-gp modulation on the analgesic effect and brain uptake of methadone, as well as identify the most relevant site via dual oral and intravenous (i.v.) experiments. The P-gp specific inhibitor (valspodar or PSC833) was preadministered (10 mg kg−1 i.v.) to test groups. Analgesia was measured using the tailflick test. The ED50 for oral methadone (2, 3, 6 and 8 mg kg−1) decreased three-fold in valspodar groups compared with controls (2.23 + 0.002 mg kg−1 and 6.07 + 0.07 mg kg−1; P &lt; 0.0001). The overall analgesic effect (% antinociception) was elevated 3.1 times in pretreated compared with control rats (90.65% + 0.22 vs 29.23% + 14.0; P &lt; 0.01) after 6 mg kg−1 oral methadone and 2.8 times after i.v. (0.35 mg kg−1) administration (91.75% + 4.27 vs 32.45% + 9.0; P &lt; 0.01). The brain:plasma distribution ratio was higher in pretreated animals and AUCbrain (overall brain concentration) was 6 times higher after oral methadone and 4 times higher after i.v. compared with controls, disproportionally increased relative to plasma, implying an active process at the BBB. P-gp, and hence substrate comedication, plays a critical role in the evolution of the methadone analgesic effect and in its brain uptake, independent of the administration route.

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.