Intraoperative methadone: rediscovery, reappraisal, and reinvigoration?

Postoperative Pain Management in Pediatric Spinal Fusion Surgery for Idiopathic Scoliosis

This article reviews and summarizes current evidence and knowledge gaps regarding postoperative analgesia after pediatric posterior spine fusion for adolescent idiopathic scoliosis, a common procedure that results in severe acute postoperative pain. Inadequate analgesia may delay recovery, cause patient dissatisfaction, and increase chronic pain risk. Despite significant adverse effects, opioids are the analgesic mainstay after scoliosis surgery. However, growing emphasis on opioid minimization and enhanced recovery has increased adoption of multimodal analgesia (MMA) regimens. While opioid adverse effects remain a concern, MMA protocols must also consider risks and benefits of adjunct medications. We discuss use of opioids via different administration routes and elaborate on the effect of MMA components on opioid/pain and recovery outcomes including upcoming regional analgesia. We also discuss risk for prolonged opioid use after surgery and chronic post-surgical pain risk in this population. Evidence supports use of neuraxial opioids at safe doses, low-dose ketorolac, and methadone for postoperative analgesia. There may be a role for low-dose ketamine in those who are opioid-tolerant or have chronic pain, but the evidence for preoperative gabapentinoids and intravenous lidocaine is currently insufficient. There is a need for further studies to evaluate pediatric-specific optimal MMA dosing regimens after scoliosis surgery. Questions remain regarding how best to prevent acute opioid tolerance, opioid-induced hyperalgesia, and chronic postsurgical pain. We anticipate that this timely update will enable clinicians to develop efficient pain regimens and provide impetus for future research to optimize recovery outcomes after spine fusion.

Methadone for Pain Management: A Pharmacotherapeutic Review

Methadone is increasingly being used for its analgesic properties. Despite the increasing popularity, many healthcare providers are not familiar with methadone's complex pharmacology and best practices surrounding its use. The purpose of this narrative review article is to discuss the pharmacology of methadone, the evidence surrounding methadone's use in acute pain management and both chronic cancer and non-cancer pain settings, as well as highlight pertinent safety, monitoring, and opioid rotation considerations. Methadone has a unique mechanism of action when compared with all other opioids and for this reason methadone has come to hold a niche role in the management of opioid-induced hyperalgesia and central sensitization. Understanding of the mechanisms of variability in methadone disposition and drug interactions has evolved over the years, with the latest evidence revealing that CYP 2B6 is the major determinant of methadone elimination and plays a key role in methadone-related drug interactions. From an acute pain perspective, most studies evaluating the use of intraoperative intravenous methadone have reported lower pain scores and post-operative opioid requirements. Oral methadone is predominantly used as a second-line opioid treatment for select chronic pain conditions. As a result, several oral morphine to oral methadone conversion ratios have been proposed, as have methods in which to rotate to methadone. From an efficacy standpoint, limited literature exists regarding the effectiveness of methadone in the chronic pain setting with most of the available efficacy data pertaining to methadone's use in the treatment of cancer pain. Many of the prospective studies that exist feature low participant numbers. Few clinical trials investigating the role of methadone as an analgesic treatment are currently underway. The complicated pharmacokinetic properties of methadone and risks of harm associated with this drug highlight how critically important it is that healthcare providers understand these features before prescribing/dispensing methadone. Particular caution is required when converting patients from other opioids to methadone and for this reason only experienced healthcare providers should undertake such a task. Further randomized trials with larger sample sizes are needed to better define the effective and safe use of methadone for pain management.

Intra-operative methadone effect on quality of recovery compared with morphine following laparoscopic gastroplasty: a randomised controlled trial

The effect of intra-operative intravenous methadone on quality of postoperative recovery was compared with morphine after laparoscopic gastroplasty. We included 137 adult patients with a body mass index > 35 kg.m^-2 who underwent bariatric surgery. Patients were allocated at random to receive either intra-operative methadone (n = 69) or morphine (n = 68). All patients received the same postoperative care and analgesia. The primary outcome of postoperative quality of recovery was assessed using the Quality of Recovery-40 questionnaire total score 24 h after surgery. Secondary outcomes were assessed in the post-anaesthesia care unit the night of the day of surgery (T1), in the morning after surgery (T2); and at night on the day following surgery (T3). The median (IQR [range]) total Quality of Recovery-40 questionnaire score of 194 (190-197 [165-200]) was higher (p < 0.0001) in the methadone group compared with the score of 181 (174-185.5 [121-200]) in the morphine group. In the post-anaesthesia care unit, the pain burden; incidence of nausea and vomiting; rescue morphine dose; and time to discharge, were significantly lower in the methadone group. On the ward, the methadone group had a lower: incidence of rescue morphine requests at T1 (5.8 vs. 54.4%, p < 0.0001) and T2 (0 vs. 20.1%, p < 0.0001); and incidence of nausea (21.7 vs. 41.2%, p = 0.014), compared with the morphine group. We conclude that intra-operative intravenous methadone improved quality of recovery in patients who underwent laparoscopic gastroplasty, compared with intra-operative morphine. Methadone also reduced postoperative pain, postoperative opioid consumption and the incidence of opioid-related adverse events.

The effect of intraoperative methadone during pediatric cardiac surgery on postoperative opioid requirements

BACKGROUND

Pain control in pediatric patients undergoing cardiac surgery presents a unique challenge. Postoperatively, many of these patients require long-term opioid infusions and sedation leading to need for prolonged weaning from opioids and longer hospital stays. We hypothesized that intravenous methadone as the sole opioid in children having cardiac surgery with cardiopulmonary bypass would improve perioperative pain control and decrease overall perioperative use of opioid analgesics and sedatives.

METHODS

We instituted a practice change involving pediatric patients aged <18 years who underwent cardiac surgery with cardiopulmonary bypass over a 14-month period, comparing the patient population who had surgery prior to the institution of intraoperative methadone usage to patients who had surgery in the months following. We then separated patients into two groups: neonatal (aged < 30 days) and non-neonatal (aged > 30 days to 18 years). Our primary outcome was intraoperative and postoperative opioid requirements measured in morphine equivalents intraoperatively, during the first 24 hours postoperatively, and up to postoperative day 7. Secondary outcomes included extubation rates in the OR, pain and sedation scores, sedation requirements, and time to start of oxycodone.

RESULTS

Patients in both groups had similar demographics. In neonatal patients, the postintervention group required significantly lower doses of intraoperative opioids. There was no statistically significant difference in postoperative opioid use. In non-neonatal patients, the postintervention group required significantly less intraoperative opioids. Postoperatively, those in the postintervention group required significantly less opioids in the first 24 hours.

CONCLUSION

The use of intraoperative methadone appears to be a reasonable alternative to the use of fentanyl with potential other benefits both intra- and postoperatively of decreased total dose of opioids and other sedatives. Future studies will assess for any improvement in total postoperative opioid requirements during the total hospital stay, and potential use of methadone by the ICU team.

Methadone for postoperative analgesia: contribution of N-methyl-D-aspartate receptor antagonism: A randomised controlled trial

BACKGROUND

Over the past number of years, N-methyl-D-aspartate (NMDA) inhibitory drugs, like ketamine, have been introduced as adjuvant treatments for postoperative acute pain, within a multimodal approach. A further extension of this strategy could be the use of opioids with NMDA receptor (NMDAr) antagonism activity for control of postoperative pain. Methadone has a unique pharmacodynamic profile: it is both a μ-agonist and an NMDAr-blocker.

OBJECTIVE

We designed this study to investigate the precise contribution of NMDAr antagonism in methadone-induced analgesia.

DESIGN

Single-centre, prospective, randomised, double-blind study.

SETTING

National Cancer Center - Fondazione IRCCS Istituto Nazionale Tumori Milano; patients were recruited between March 2010 and June 2012.

PATIENTS

Ninety-six patients scheduled for an open laparotomy for anterior resection of the rectum.

INTERVENTIONS

We randomly assigned patients to four groups: 0-Mo (placebo and morphine), K-Mo [S(+)-ketamine and morphine], 0-Me (placebo and methadone), K-Me [S(+)-ketamine and methadone].

MAIN OUTCOME MEASURES

The primary end-point was the extent of mechanical static (punctuate) hyperalgesia to von Frey hair stimulation lateral to the surgical incision.

RESULTS

Peri-incisional hyperalgesia was 8.4 cm (95% confidence interval, 1.5 to 15.41) lower in the treatment group (K-Me) compared with the control group (0-Mo) at 24 h after surgery (P = 0.02). No significant differences were observed between the groups at 48 h after surgery (P = 0.88). Both groups treated with methadone had significantly lower pain during rest and movement, as measured with a Numerical Rating Scale at 24 h. At 48 h, only the movement Numerical Rating Scale was significantly lower. No difference occurred in opioid consumption.

CONCLUSION

Methadone provides effective control of acute postoperative pain, independently, by modulation of the hyperalgesia mechanism.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, no.: NCT01594047.

Methadone versus morphine for postoperative pain in patients undergoing surgery for gynecological cancer: A randomized controlled clinical trial

STUDY OBJECTIVE

The aim of this study was to compare methadone and morphine for the management of postoperative.

DESIGN

Open, controlled study.

SETTING

Postoperative recovering area, ward.

PATIENTS

Sixty-four patients, ASA I-III, undergoing gynecological surgery for cancer.

INTERVENTIONS

Morphine or methadone 0.15 mg/kg given preoperatively. After operation an intravenous morphine or intravenous methadone infusion at doses of 12 mg/day was started.

MEASUREMENTS

Pain intensity and opioid consumption.

MAIN RESULTS

Methadone infusion provided a better analgesia in comparison with morphine infusion on the second day. Opioid consumption was significantly lower in the methadone group. No episodes of relevant desaturation or signs of respiratory depression were recorded.

CONCLUSION

A preoperative bolus of methadone, followed by a continuous infusion of low doses post-operatively, provided a better analgesia, without adding risk of adverse effects, in comparison with morphine.

Postoperative Pain and Analgesic Requirements in the First Year after Intraoperative Methadone for Complex Spine and Cardiac Surgery

BACKGROUND

Methadone is a long-acting opioid that has been reported to reduce postoperative pain scores and analgesic requirements and may attenuate development of chronic postsurgical pain. The aim of this secondary analysis of two previous trials was to follow up with patients who had received a single intraoperative dose of either methadone or traditional opioids for complex spine or cardiac surgical procedures.

METHODS

Preplanned analyses of long-term outcomes were conducted for spinal surgery patients randomized to receive 0.2 mg/kg methadone at the start of surgery or 2 mg hydromorphone at surgical closure, and for cardiac surgery patients randomized to receive 0.3 mg/kg methadone or 12 μg/kg fentanyl intraoperatively. A pain questionnaire assessing the weekly frequency (the primary outcome) and intensity of pain was mailed to subjects 1, 3, 6, and 12 months after surgery. Ordinal data were compared with the Mann-Whitney U test, and nominal data were compared using the chi-square test or Fisher exact probability test. The criterion for rejection of the null hypothesis was P < 0.01.

RESULTS

Three months after surgery, patients randomized to receive methadone for spine procedures reported the weekly frequency of chronic pain was less (median score 0 on a 0 to 4 scale [less than once a week] vs. 3 [daily] in the hydromorphone group, P = 0.004). Patients randomized to receive methadone for cardiac surgery reported the frequency of postsurgical pain was less at 1 month (median score 0) than it was in patients randomized to receive fentanyl (median score 2 [twice per week], P = 0.004).

CONCLUSIONS

Analgesic benefits of a single dose of intraoperative methadone were observed during the first 3 months after spinal surgery (but not at 6 and 12 months), and during the first month after cardiac surgery, when the intensity and frequency of pain were the greatest.

Intraoperative Methadone in Same-Day Ambulatory Surgery: A Randomized, Double-Blinded, Dose-Finding Pilot Study

BACKGROUND

Approximately 50 million US patients undergo ambulatory surgery annually. Postoperative opioid overprescribing is problematic, yet many patients report inadequate pain relief. In major inpatient surgery, intraoperative single-dose methadone produces better analgesia and reduces opioid use compared with conventional repeated dosing of short-duration opioids. This investigation tested the hypothesis that in same-day ambulatory surgery, intraoperative methadone, compared with short-duration opioids, reduces opioid consumption and pain, and determined an effective intraoperative induction dose of methadone for same-day ambulatory surgery.

METHODS

A double-blind, dose-escalation protocol randomized 60 patients (2:1) to intraoperative single-dose intravenous methadone (initially 0.1 then 0.15 mg/kg ideal body weight) or conventional as-needed dosing of short-duration opioids (eg, fentanyl, hydromorphone; controls). Intraoperative and postoperative opioid consumption, pain, and opioid side effects were assessed before discharge. Patient home diaries recorded pain, opioid use, and opioid side effects daily for 30 days postoperatively. Primary outcome was in-hospital (intraoperative and postoperative) opioid use. Secondary outcomes were 30 days opioid consumption, pain intensity, and opioid side effects.

RESULTS

Median (interquartile range) methadone doses were 6 (5-6) and 9 (8-9) mg in the 0.1 and 0.15 mg/kg methadone groups, respectively. Total opioid consumption (morphine equivalents) in the postanesthesia care unit was significantly less compared with controls (9.3 mg, 1.3-11.0) in subjects receiving 0.15 mg/kg methadone (0.1 mg, 0.1-3.3; P < .001) but not 0.1 mg/kg methadone (5.0 mg, 3.3-8.1; P = .60). Dose-escalation ended at 0.15 mg/kg methadone. Total in-hospital nonmethadone opioid use after short-duration opioid, 0.1 mg/kg methadone, and 0.15 mg/kg methadone was 35.3 (25.0-44.0), 7.1 (3.7-10.0), and 3.3 (0.1-5.8) mg morphine equivalents, respectively (P < .001 for both versus control). In-hospital pain scores and side effects were not different between groups. In the 30 days after discharge, patients who received methadone 0.15 mg/kg had less pain at rest (P = .02) and used fewer opioid pills than controls (P < .0001), whereas patients who received 0.1 mg/kg had no difference in pain at rest (P = .69) and opioid use compared to controls (P = .08).

CONCLUSIONS

In same-day discharge surgery, this pilot study identified a single intraoperative dose of methadone (0.15 mg/kg ideal body weight), which decreased intraoperative and postoperative opioid requirements and postoperative pain, compared with conventional intermittent short-duration opioids, with similar side effects.

Intraoperative Methadone Reduces Pain and Opioid Consumption in Acute Postoperative Pain: A Systematic Review and Meta-analysis

BACKGROUND

Methadone is a potent opioid exerting an analgesic effect through N-methyl-D-aspartate receptor antagonism and the inhibition of serotonin and noradrenaline reuptake. It has also been used in several procedures to reduce postoperative pain and opioid use. This meta-analysis aimed to determine whether the intraoperative use of methadone lowers postoperative pain scores and opioid consumption in comparison to other opioids.

METHODS

Double-blinded, controlled trials without language restrictions were included from MEDLINE, Embase, LILACS, The Cochrane Central Register of Controlled Trials (CENTRAL), and CINAHL via EBSCOhost. The included studies tracked total opioid consumption, postoperative pain scores, opioid-related side effects, and patient satisfaction until 72 hours postoperatively. Mean difference (MD) was used for effect size.

RESULTS

In total, 476 articles were identified and 13 were considered eligible for inclusion in the meta-analysis. In 486 patients (7 trials), pain at rest (MD, 1.09; 95% confidence interval (CI), 1.47-0.72; P < .00001) and at movement (MD, 2.48; 95% CI, 3.04-1.92; P = .00001) favored methadone 24 hours after surgery. In 374 patients (6 trials), pain at rest (MD, 1.47; 95% CI, 3.04-1.02; P < .00001) and at movement (MD, 2.03; 95% CI, 3.04-1.02; P < .00001) favored methadone 48 hours after surgery. In 320 patients (4 trials), pain at rest (MD, 1.02; 95% CI, 1.65-0.39; P = .001) and at movement (MD, 1.34; 95% CI, 1.82-0.87; P < .00001) favored methadone 72 hours after surgery. A Trial Sequential Analysis was performed and the Z-cumulative curve for methadone crossed the monitoring boundary at all evaluations, additionally crossing Required Information Size at 24 and 48 hours at rest. Methadone group also showed lower postoperative opioid consumption in morphine equivalent dosage (mg) at 24 hours (MD, 8.42; 95% CI, 12.99-3.84 lower; P < .00001), 24-48 hours (MD, 14.33; 95% CI, 26.96-1.91 lower; P < .00001), 48-72 hours (MD, 3.59; 95% CI, 6.18-1.0 lower; P = .007) postoperatively.

CONCLUSIONS

Intraoperative use of methadone reduced postoperative pain scores compared to other opioids, and Trial Sequential Analysis suggested that no more trials are required to confirm pain reduction at rest until 48 hours after surgery. Methadone also reduced postoperative opioid consumption and led to better patient satisfaction scores through 72 hours postoperatively compared to other opioids.

Intraoperative methadone for postoperative pain management - systematic review protocol

Methadone is a long acting opioid initially used to treat opioid withdrawal symptoms. It has been suggested that methadone, when given as a single bolus while under anesthesia, provides good postoperative analgesia and is associated with minimal risk of opioid adverse events. Several small studies have investigated the use of methadone for postoperative analgesia with some promising results. Here we describe our protocol for a meta-analysis to investigate the postoperative analgesic effect of methadone.

Preoperative oral methadone for postoperative pain in patients undergoing cardiac surgery: A randomized double-blind placebo-controlled pilot

Background: Inadequately controlled sternotomy pain after cardiac surgery can lead to delayed recovery and patient suffering. Preoperative intravenous methadone is effective for reducing both postoperative pain and opioid consumption. Despite ease of administration, the effects of preoperative oral methadone are not well described in the literature.

Aims: This pilot study investigated the effect of preoperative oral methadone on pain scores, analgesia requirements, and opioid-induced side effects.

Methods: A randomized double-blind placebo-controlled model was used with sampling of patients undergoing sternotomy for isolated coronary artery bypass graft (CABG) surgery (ClinicalTrials.gov registration no. NCT02774499). Participants were randomized to receive oral methadone (0.3 mg/kg) or oral placebo prior to entering the operating room. The primary outcome was pain scores on a 0–10 Verbal Rating Scale. Secondary outcomes included morphine requirements using patient-controlled analgesia (PCA), time to extubation, level of sedation, and side effects such as nausea, vomiting, pruritus, hypoventilation, and hypoxia over a 72-h monitoring time.

Results: Twenty-one patients completed the study. Oral methadone did not reduce pain scores in the methadone group (P = 0.08). However, postoperative morphine requirement during the first 24 h was reduced by a mean of 23 mg in the methadone group (mean difference, −23; 99% confidence interval [CI], 37–13 mg; P < 0.005). No reduction in pain scores or PCA morphine was observed beyond 24 h postoperatively. There was no difference in incidence of opioid-related side effects between groups throughout the postoperative period.

Conclusions: Though preoperative oral methadone did not reduce pain scores, morphine requirements were reduced in the first 24 h post-CABG.

Intraoperative use of methadone improves control of postoperative pain in morbidly obese patients: a randomized controlled study

Objectives

Surgical patients still commonly experience postoperative pain. With the increasing prevalence of obesity, there is a growing demand for surgical procedures by this population. Intraoperative use of methadone has not been well assessed in this population.

Materials and methods

Patients with a body mass index of 35 kg/m² or more undergoing bariatric surgery were randomly assigned to receive either fentanyl (group F) or methadone (group M) in anesthesia induction and maintenance. The primary outcome was morphine consumption during the first 24 hours after surgery through a patient-controlled analgesia device. Secondary outcomes were pain scores at rest and while coughing, opioid related side effects, and patient satisfaction. The patients were also evaluated 3 months after surgery for the presence of pain, dysesthesia, or paresthesia at surgical site.

Results

Postoperative morphine consumption was significantly higher for patients receiving fentanyl than methadone during the postoperative period at 2 hours (mean difference [MD] 6.4 mg; 95% CI 3.1-9.6; P<0.001), 2-6 hours (MD 11.4 mg; 95% CI 6.5-16.2; P<0.001), 6-24 hours (MD 10.4 mg; 95% CI 5.0-15.7; P<0.001), and 24-48 hours (MD 14.5 mg; 95% CI 3.9-25.1; P=0.01). Patients from group F had higher pain scores until 24 hours postoperatively, higher incidence of nausea and vomiting, lower satisfaction, and more evoked pain at surgical scar at the 3-month postoperative evaluation than group M.

Conclusion

Intraoperative methadone can safely lower postoperative opioid consumption and improve postoperative pain scores compared with fentanyl in morbidly obese patients.

Safety profile of intraoperative methadone for analgesia after major spine surgery: An observational study of 1,478 patients

OBJECTIVE

To investigate the incidence of perioperative adverse events in patients receiving intravenous methadone for major spine surgery.

DESIGN

Retrospective review of perioperative records from March 2011 and February 2016.

SETTING

University of Virginia Healthsystem.

PATIENTS

Adult patients undergoing elective spinal fusion of two or more levels.

MAIN OUTCOME MEASURES

Incidence of respiratory depression, time to extubation, hypotension, hypoxemia, reintubation, cardiac complications, and death.

RESULTS

Reviewed 1,478 patient records. Mean intraoperative methadone dose was 0.14 ± 0.07 mg/kg. A total of 1,142 patients (77.4 percent) were extubated in the operating room, 543 (36.8 percent) experienced respiratory depression, 1,180 (79.8 percent) hypoxemia, and 22 (1.5 percent) required reintubation. Cardiac complications included arrhythmias (289 patients, 29.9 percent), QTc prolongation (568 patients, 58.8 percent), and myocardial infarction (16 patients, 1.1 percent). Two in hospital deaths occurred (0.14 percent).

CONCLUSIONS

Mild-moderate respiratory depression is observed following a one-time dose of intraoperative methadone, and monitoring in an appropriate postoperative setting is recommended.

[Comparison of postoperative analgesia with methadone versus morphine in cardiac surgery]

BACKGROUND AND OBJECTIVES

Pain is an aggravating factor of postoperative morbidity and mortality. The aim of this study was to compare the effects of methadone versus morphine using the numerical rating scale of pain and postoperative on-demand analgesia in patients undergoing myocardial revascularization.

METHOD

A randomized, double-blind, parallel clinical trial was performed with patients undergoing coronary artery bypass grafting. The subjects were randomly divided into two groups: morphine group and methadone group. At the end of cardiac surgery, 0.1 mg.kg−1 adjusted body weight of methadone or morphine was administered intravenously. Patients were referred to the ICU, where the following was assessed: extubation time, time to first analgesic request, number of analgesic and antiemetic drug doses within 36 h, numerical pain scale at 12, 24, and 36 h postoperatively, and occurrence of adverse effects.

RESULTS

Each group comprised 50 patients. Methadone showed 22% higher efficacy than morphine as it yielded a number-needed-to-treat score of 6 and number-needed-to-harm score of 16. The methadone group showed a mean score of 1.9 ± 2.2 according to the numerical pain scale at 24 h after surgery, whereas as the morphine group showed a mean score of 2.9 ± 2.6 (p = 0.029). The methadone group required less morphine (29%) than the morphine group (43%) (p = 0.002). However, the time to first analgesic request in the postoperative period was 145.9 ± 178.5 min in the methadone group, and 269.4 ± 252.9 in the morphine group (p = 0.005).

CONCLUSIONS

Methadone was effective for analgesia in patients undergoing coronary artery bypass grafting without extracorporeal circulation.

Clinical Effectiveness and Safety of Intraoperative Methadone in Patients Undergoing Posterior Spinal Fusion Surgery

Background

Patients undergoing spinal fusion surgery often experience severe pain during the first three postoperative days. The aim of this parallel-group randomized trial was to assess the effect of the long-duration opioid methadone on postoperative analgesic requirements, pain scores, and patient satisfaction after complex spine surgery.

Methods

One hundred twenty patients were randomized to receive either methadone 0.2 mg/kg at the start of surgery or hydromorphone 2 mg at surgical closure. Anesthetic care was standardized, and clinicians were blinded to group assignment. The primary outcome was intravenous hydromorphone consumption on postoperative day 1. Pain scores and satisfaction with pain management were measured at postanesthesia care unit admission, 1 and 2 h postadmission, and on the mornings and afternoons of postoperative days 1 to 3.

Results

One hundred fifteen patients were included in the analysis. Median hydromorphone use was reduced in the methadone group not only on postoperative day 1 (4.56 vs. 9.90 mg) but also on postoperative days 2 (0.60 vs. 3.15 mg) and 3 (0 vs. 0.4 mg; all P&lt; 0.001). Pain scores at rest, with movement, and with coughing were less in the methadone group at 21 of 27 assessments (all P = 0.001 to &lt; 0.0001). Overall satisfaction with pain management was higher in the methadone group than in the hydromorphone group until the morning of postoperative day 3 (all P = 0.001 to &lt; 0.0001).

Conclusions

Intraoperative methadone administration reduced postoperative opioid requirements, decreased pain scores, and improved patient satisfaction with pain management.

Pharmacokinetics and analgesic effects of methadone in children and adults with sickle cell disease

BACKGROUND

Vaso-occlusive episodes (VOEs) are a significant source of morbidity among children and adults with sickle cell disease (SCD). There is little information on methadone use for SCD pain. This investigation evaluated methadone pharmacokinetics in children and adults with SCD, with a secondary aim to assess pain relief and opioid consumption.

PROCEDURE

Participants included children (<18 years) and adults with a VOE requiring hospitalization. Patients were randomly assigned to receive standard care (opioid patient-controlled analgesia; control group) or one dose of intravenous methadone (0.1-0.125 mg/kg) in addition to standard care (methadone group). Venous methadone and metabolite concentrations were measured. Pain scores, pain relief scores, and opioid consumption were recorded.

RESULTS

Twenty-four children (12 methadone, 12 controls) and 23 adults (11 methadone, 12 controls) were studied. In children, the half-life of R- and S-methadone enantiomers was 34 ± 16 and 24 ± 9 hr, respectively. In adults, R- and S-methadone half-lives were 52 ± 17 and 38 ± 12 hr, respectively. Pain scores were lower (P = 0.002) and pain relief scores were higher (P = 0.0396) in children receiving methadone versus controls. There was no difference in pain scores and pain relief in adults receiving methadone versus controls. There was no difference in opioid consumption between methadone and control groups, in both adults and children.

CONCLUSIONS

Intravenous methadone disposition in children and adults with SCD was comparable to that in subjects without SCD from prior studies. Methadone produced more pain relief than standard care in children with SCD. Higher methadone doses may be more effective and should be evaluated in both children and adults with SCD.

Perioperative management of a morbidly obese pregnant patient undergoing cesarean section under general anesthesia - case report

BACKGROUND AND OBJECTIVES

The increased prevalence of obesity in the general population extends to women of reproductive age. The aim of this study is to report the perioperative management of a morbidly obese pregnant woman, body mass index >50kg/m(2), who underwent cesarean section under general anesthesia.

CASE REPORT

Pregnant woman in labor, 35 years of age, body mass index 59.8kg/m(2). Cesarean section was indicated due to the presumed fetal macrosomia. The patient refused spinal anesthesia. She was placed in the ramp position with cushions from back to head to facilitate tracheal intubation. Another cushion was placed on top of the right gluteus to create an angle of approximately 15° to the operating table. Immediately before induction of anesthesia, asepsis was carried out and sterile surgical fields were placed. Anesthesia was induced in rapid sequence, with Sellick maneuver and administration of remifentanil, propofol, and succinilcolina. Intubation was performed using a gum elastic bougie, and anesthesia was maintained with sevoflurane and remifentanil. The interval between skin incision and fetal extraction was 21min, with the use of a Simpson's forceps scoop to assist in the extraction. The patient gave birth to a newborn weighing 4850g, with Apgar scores of 2 in the 1st minute (received positive pressure ventilation by mask for about 2min) and 8 in the 5th minute. The patient was extubated uneventfully. Multimodal analgesia and prophylaxis of nausea and vomiting was performed. Mother and newborn were discharged on the 4th postoperative day.

Methadone Pharmacogenetics: CYP2B6 Polymorphisms Determine Plasma Concentrations, Clearance, and Metabolism

BACKGROUND

Interindividual variability in methadone disposition remains unexplained, and methadone accidental overdose in pain therapy is a significant public health problem. Cytochrome P4502B6 (CYP2B6) is the principle determinant of clinical methadone elimination. The CYP2B6 gene is highly polymorphic, with several variant alleles. CYP2B6.6, the protein encoded by the CYP2B6*6 polymorphism, deficiently catalyzes methadone metabolism in vitro. This investigation determined the influence of CYP2B6*6, and other allelic variants encountered, on methadone concentrations, clearance, and metabolism.

METHODS

Healthy volunteers in genotype cohorts CYP2B6*1/*1 (n = 21), CYP2B6*1/*6 (n = 20), and CYP2B6*6/*6 (n = 17), and also CYP2B6*1/*4 (n = 1), CYP2B6*4/*6 (n = 3), and CYP2B6*5/*5 (n = 2) subjects, received single doses of IV and oral methadone. Plasma and urine methadone and metabolite concentrations were determined by tandem mass spectrometry.

RESULTS

Average S-methadone apparent oral clearance was 35 and 45% lower in CYP2B6*1/*6 and CYP2B6*6/*6 genotypes, respectively, compared with CYP2B6*1/*1. R-methadone apparent oral clearance was 25 and 35% lower in CYP2B6*1/*6 and CYP2B6*6/*6 genotypes, respectively, compared with CYP2B6*1/*1. R- and S-methadone apparent oral clearance was threefold and fourfold greater in CYP2B6*4 carriers. IV and oral R- and S-methadone metabolism was significantly lower in CYP2B6*6 carriers compared with that of CYP2B6*1 homozygotes and greater in CYP2B6*4 carriers. Methadone metabolism and clearance were lower in African Americans in part because of the CYP2B6*6 genetic polymorphism.

CONCLUSIONS

CYP2B6 polymorphisms influence methadone plasma concentrations, because of altered methadone metabolism and thus clearance. Genetic influence is greater for oral than IV methadone and S- than R-methadone. CYP2B6 pharmacogenetics explains, in part, interindividual variability in methadone elimination. CYP2B6 genetic effects on methadone metabolism and clearance may identify subjects at risk for methadone toxicity and drug interactions.

Intraoperative Methadone for the Prevention of Postoperative Pain

Background:

The intensity of pain after cardiac surgery is often underestimated, and inadequate pain control may be associated with poorer quality of recovery. The aim of this investigation was to examine the effect of intraoperative methadone on postoperative analgesic requirements, pain scores, patient satisfaction, and clinical recovery.

Methods:

Patients undergoing cardiac surgery with cardiopulmonary bypass (n = 156) were randomized to receive methadone (0.3 mg/kg) or fentanyl (12 μg/kg) intraoperatively. Postoperative analgesic requirements were recorded. Patients were assessed for pain at rest and with coughing 15 min and 2, 4, 8, 12, 24, 48, and 72 h after tracheal extubation. Patients were also evaluated for level of sedation, nausea, vomiting, itching, hypoventilation, and hypoxia at these times.

Results:

Postoperative morphine requirements during the first 24 h were reduced from a median of 10 mg in the fentanyl group to 6 mg in the methadone group (median difference [99% CI], −4 [−8 to −2] mg; P &lt; 0.001). Reductions in pain scores with coughing were observed during the first 24 h after extubation; the level of pain with coughing at 12 h was reduced from a median of 6 in the fentanyl group to 4 in the methadone group (−2 [−3 to −1]; P &lt; 0.001). Improvements in patient-perceived quality of pain management were described in the methadone group. The incidence of opioid-related adverse events was not increased in patients administered methadone.

Conclusions:

Intraoperative methadone administration resulted in reduced postoperative morphine requirements, improved pain scores, and enhanced patient-perceived quality of pain management.

Influence of HIV antiretrovirals on methadone N-demethylation and transport

Drug interactions involving methadone and/or HIV antiretrovirals can be problematic. Mechanisms whereby antiretrovirals induce clinical methadone clearance are poorly understood. Methadone is N-demethylated to 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) by CYP2B6 and CYP3A4 in vitro, but by CYP2B6 in vivo. This investigation evaluated human hepatocytes as a model for methadone induction, and tested the hypothesis that methadone and EDDP are substrates for human drug transporters. Human hepatocyte induction by several antiretrovirals of methadone N-demethylation, and CYP2B6 and CYP3A4 transcription, protein expression and catalytic activity, and pregnane X receptor (PXR) activation were evaluated. Methadone and EDDP uptake and efflux by overexpressed transporters were also determined. Methadone N-demethylation was generally not significantly increased by the antiretrovirals. CYP2B6 mRNA and activity (bupropion N-demethylation) were induced by several antiretrovirals, as were CYP3A4 mRNA and protein expression, but only indinavir increased CYP3A activity (alfentanil dealkylation). CYP upregulation appeared related to PXR activation. Methadone was not a substrate for uptake (OCT1, OCT2, OCT3, OATP1A2, OATP1B1, OATP1B3, OATP2B1) or efflux (P-gp, BCRP) transporters. EDDP was a good substrate for P-gp, BCRP, OCT1, OCT3, OATP1A2, and OATP1B1. OATP1A2- and OCT3-mediated EDDP uptake, and BCRP-mediated EDDP efflux transport, was inhibited by several antiretrovirals. Results show that hepatocyte methadone N-demethylation resembles expressed and liver microsomal metabolism more than clinical metabolism. Compared with clinical studies, hepatocytes underreport induction of methadone metabolism by HIV drugs. Hepatocytes are not a good predictive model for clinical antiretroviral induction of methadone metabolism and not a substitute for clinical studies. EDDP is a transporter substrate, and is susceptible to transporter-mediated interactions.

[Perioperative management of a morbidly obese pregnant patient undergoing cesarean section under general anesthesia - case report]

BACKGROUND AND OBJECTIVES

The increased prevalence of obesity in the general population extends to women of reproductive age. The aim of this study is to report the perioperative management of a morbidly obese pregnant woman, body mass index > 50 kg/m(2), who underwent cesarean section under general anesthesia.

CASE REPORT

Pregnant woman in labor, 35 years of age, body mass index 59.8 kg/m(2). Caesarean section was indicated due to the presumed fetal macrosomia. The patient refused spinal anesthesia. She was placed in the ramp position with cushions from back to head to facilitate tracheal intubation. Another cushion was placed on top of the right gluteus to create an angle of approximately 15° to the operating table. Immediately before induction of anesthesia, asepsis was carried out and sterile surgical fields were placed. Anesthesia was induced in rapid sequence, with Sellick maneuver and administration of remifentanil, propofol, and succinilcolina. Intubation was performed using a gum elastic bougie, and anesthesia was maintained with sevoflurane and remifentanil. The interval between skin incision and fetal extraction was 21 minutes, with the use of a Simpson's forceps scoop to assist in the extraction. The patient gave birth to a newborn weighing 4850 g, with Apgar scores of 2 in the 1(st) minute (received positive pressure ventilation by mask for about 2 minutes) and 8 in the 5(th) minute. The patient was extubated uneventfully. Multimodal analgesia and prophylaxis of nausea and vomiting was performed. Mother and newborn were discharged on the 4(th) postoperative day.

Automated radiochemical synthesis and biodistribution of [¹¹C]l-α-acetylmethadol ([¹¹C]LAAM)

Long-acting opioid agonists methadone and l-α-acetylmethadol (LAAM) prevent withdrawal in opioid-dependent persons. Attempts to synthesize [(11)C]-methadone for PET evaluation of brain disposition were unsuccessful. Owing, however, to structural and pharmacologic similarities, we aimed to develop [(11)C]LAAM as a PET ligand to probe the brain exposure of long-lasting opioids in humans. This manuscript describes [(11)C]LAAM synthesis and its biodistribution in mice. The radiochemical synthetic strategy afforded high radiochemical yield, purity and specific activity, thereby making the synthesis adaptable to automated modules.

Cyclosporine-inhibitable blood-brain barrier drug transport influences clinical morphine pharmacodynamics

BACKGROUND

The blood-brain barrier is richly populated by active influx and efflux transporters influencing brain drug concentrations. Morphine, a drug with delayed clinical onset, is a substrate for the efflux transporter P-glycoprotein in vitro and in animals. This investigation tested whether morphine is a transporter substrate in humans.

METHODS

Fourteen healthy volunteers received morphine (0.1 mg/kg, 1-h IV infusion) in a crossover study without (control) or with the infusion of validated P-glycoprotein inhibitor cyclosporine (5 mg/kg, 2-h infusion). Plasma and urine morphine and morphine glucuronide metabolite concentrations were measured by mass spectrometry. Morphine effects were measured by miosis and analgesia.

RESULTS

Cyclosporine minimally altered morphine disposition, increasing the area under the plasma morphine concentration versus time curve to 100 ± 21 versus 85 ± 24 ng/ml·h (P < 0.05) without changing maximum plasma concentration. Cyclosporine enhanced (3.2 ± 0.9 vs. 2.5 ± 1.0 mm peak) and prolonged miosis, and increased the area under the miosis-time curve (18 ± 9 vs. 11 ± 5 mm·h), plasma effect-site transfer rate constant (k(e0), median 0.27 vs. 0.17 h(-1)), and maximum calculated effect-site morphine concentration (11.5 ± 3.7 vs. 7.6 ± 2.9 ng/ml; all P < 0.05). Analgesia testing was confounded by cyclosporine-related pain.

CONCLUSIONS

Morphine is a transporter substrate at the human blood-brain barrier. Results suggest a role for P-glycoprotein or other efflux transporters in brain morphine access, although the magnitude of the effect is small, and unlikely to be a major determinant of morphine clinical effects. Efflux may explain some variability in clinical morphine effects.

Cytochrome P4503A does not mediate the interaction between methadone and ritonavir-lopinavir

Plasma concentrations of orally administered methadone are reduced by the human immunodeficiency virus protease inhibitor combination ritonavir and lopinavir, but the mechanism is unknown. Methadone metabolism, clearance, and drug interactions have been attributed to CYP3A4, but this remains controversial. This investigation assessed the effects of acute (2 days) and steady-state (2 weeks) ritonavir-lopinavir on intravenous and oral methadone metabolism and clearance, hepatic and intestinal CYP3A4/5 activity (using the probe substrate intravenous and oral alfentanil), and intestinal transporter activity (using oral fexofenadine) in healthy volunteers. Plasma and urine concentrations of methadone and metabolite enantiomers, and other analytes, were determined by mass spectrometry. Acute and chronic ritonavir-lopinavir reduced plasma methadone enantiomer concentrations in half, with an average 2.6- and 1.5-fold induction of systemic and apparent oral methadone clearances. Induction was attributable to stereoselectively increased hepatic methadone N-demethylation, hepatic extraction, and hepatic clearance, and there was a strong correlation between methadone N-demethylation and clearance. Methadone renal clearance was unchanged. Alfentanil's systemic clearance and hepatic extraction, apparent oral clearance, and intestinal extraction were reduced to 25%, 16%, and 35% of control, indicating strong inhibition of hepatic and intestinal CYP3A activities. Ritonavir-lopinavir (acute > chronic) increased fexofenadine exposure, suggesting intestinal P-glycoprotein inhibition. No correlation was found between methadone clearance and CYP3A activity. Acute and steady-state ritonavir-lopinavir stereoselectively induced methadone N-demethylation and clearance, despite significant inhibition of hepatic and intestinal CYP3A activity. Ritonavir-lopinavir inhibited intestinal transporters activity but had no effect on methadone bioavailability. These results do not support a significant role for CYP3A or ritonavir-lopinavir-inhibitable intestinal transporters in single-dose methadone disposition.

Mechanism of autoinduction of methadone N-demethylation in human hepatocytes

BACKGROUND

There is considerable interindividual and intraindividual variability in methadone metabolism and clearance. Methadone dosing is particularly challenging during initiation of therapy, because of time-dependent increases in hepatic clearance (autoinduction). Although methadone N-demethylation is catalyzed in vitro by cytochrome P4502B6 (CYP2B6) and CYP3A4, and clearance in vivo depends on CYP2B6, mechanism(s) of autoinduction are incompletely understood. In this investigation, we determined mechanism(s) of methadone autoinduction using human hepatocytes.

METHODS

Fresh human hepatocytes were exposed to 0.1 to 10 µM methadone for 72 hours. Cells were washed and methadone N-demethylation assessed. CYP2B6, CYP3A4, and CYP3A5 messenger RNA (mRNA), protein expression (by gel-free high-performance liquid chromatography mass spectrometry) and catalytic activity (bupropion hydroxylation and alfentanil dealkylation for CYP2B6 and CYP3A4/5, respectively) were measured. Mechanisms of CYP induction were characterized using pregnane X receptor and constitutive androstane receptor reporter gene assays.

RESULTS

Methadone (10 µM) increased methadone N-demethylation 2-fold, CYP2B6 and CYP3A4 mRNA 3-fold, and protein expression 2-fold. CYP3A5 mRNA was unchanged. CYP2B6 and CYP3A4/5 activities increased 2-fold. Induction by methadone enantiomers (R-methadone versus S-methadone) did not differ. Induction was relatively weak compared with maximum induction by phenobarbital and rifampin. Lower methadone concentrations had smaller effects. Methadone was an agonist for the pregnane X receptor but not the constitutive androstane receptor.

CONCLUSIONS

Methadone caused concentration-dependent autoinduction of methadone N-demethylation in human hepatocytes, related to induction of CYP2B6 and CYP3A4 mRNA expression, protein expression, and catalytic activity. Induction was related to pregnane X receptor but not constitutive androstane receptor activation. These in vitro findings provide mechanistic insights into clinical autoinduction of methadone metabolism and clearance.

Role of cytochrome P4502B6 in methadone metabolism and clearance

Methadone N-demethylation in vitro is catalyzed by hepatic cytochrome P4502B6 (CYP2B6) and CYP3A4, but clinical disposition is often attributed to CYP3A4. This investigation tested the hypothesis that CYP2B6 is a prominent CYP isoform responsible for clinical methadone N-demethylation and clearance, using the in vivo mechanism-based CYP2B6 inhibitor ticlopidine, given orally for 4 days. A preliminary clinical investigation with the CYP3A4/5 substrate probe alfentanil established that ticlopidine did not inhibit intestinal or hepatic CYP3A4/5. Subjects received intravenous plus oral (deuterium-labeled) racemic methadone before and after ticlopidine. Ticlopidine significantly and stereoselectively (S > R) inhibited methadone N-demethylation, decreasing plasma metabolite/methadone area under the curve ratios and metabolite formation clearances. Ticlopidine also significantly increased the dose-adjusted plasma area under the curve for R- and S-methadone by 20% and 60%, respectively, after both intravenous and oral dosing. CYP2B6 inhibition reduces methadone N-demethylation and clearance, and alters methadone concentrations, demonstrating an important role for CYP2B6 in clinical methadone disposition.

The clinical significance of QT interval prolongation in anesthesia and pain management: what you should and should not worry about

The most feared drug-induced complication is fatal cardiac arrest. Torsades de pointes (TdP) is a polymorphic ventricular tachycardia occurring in the setting of a QT interval prolongation and is the most frequent type of drug-induced pro-arrhythmia. The most common mechanism of QT prolongation and TdP is blockade of the rapid component of the delayed rectifier repolarizing potassium conductance IKr. Anesthesiologists have extensive experience with QT prolonging drugs, but there are relatively few reports of TdP occurring in the perioperative setting. Nevertheless, regulatory concern regarding the drug droperidol resulted in a significant reduction in its use. Concern regarding two other agents that potently block IKr, i.e., sevoflurane and methadone, has grown, and practitioners are worried that these valuable agents may meet the same fate. In this review, the data regarding the TdP risk of droperidol, sevoflurane, and methadone are compared with particular emphasis on the different settings in which they are employed. While the three drugs are potent IKr inhibitors, little evidence exists to suggest that droperidol or sevoflurane are associated with significant proarrhythmia in the perioperative setting. Due to factors such as inhibition of the parasympathetic nervous system, prevention of hypoxia and hypercarbia, and attention to serum electrolytes, TdP is a very rare occurrence in the perioperative environment. Methadone, however, is typically given to outpatients, over long periods, and in combination with agents that inhibit its metabolism or are QT prolonging in their own right. Thus, pre- and post-drug electrocardiograms may be appropriate when prescribing methadone for outpatients, while the much lower risk for TdP (and the difficulties inherent in QT measurement in the perioperative period) render this approach unfruitful and worthy of reevaluation.

Lack of indinavir effects on methadone disposition despite inhibition of hepatic and intestinal cytochrome P4503A (CYP3A)

BACKGROUND

Methadone disposition and pharmacodynamics are highly susceptible to interactions with antiretroviral drugs. Methadone clearance and drug interactions have been attributed to cytochrome P4503A4 (CYP3A4), but actual mechanisms are unknown. Drug interactions can be clinically and mechanistically informative. This investigation assessed effects of the protease inhibitor indinavir on methadone pharmacokinetics and pharmacodynamics, hepatic and intestinal CYP3A4/5 activity (using alfentanil), and intestinal transporter activity (using fexofenadine).

METHODS

Twelve healthy volunteers underwent a sequential crossover. On three consecutive days they received oral alfentanil plus fexofenadine, intravenous alfentanil, and intravenous plus oral (deuterium-labeled) methadone. This was repeated after 2 weeks of indinavir. Plasma and urine analytes were measured by mass spectrometry. Opioid effects were measured by miosis.

RESULTS

Indinavir significantly inhibited hepatic and first-pass CYP3A activity. Intravenous alfentanil systemic clearance and hepatic extraction were reduced to 40-50% of control, apparent oral clearance to 30% of control, and intestinal extraction decreased by half, indicating 50% and 70% inhibition of hepatic and first-pass CYP3A activity. Indinavir increased fexofenadine area under the plasma concentration-time curve 3-fold, suggesting significant P-glycoprotein inhibition. Indinavir had no significant effects on methadone plasma concentrations, methadone N-demethylation, systemic or apparent oral clearance, renal clearance, hepatic extraction or clearance, or bioavailability. Methadone plasma concentration-effect relationships were unaffected by indinavir.

CONCLUSIONS

Despite significant inhibition of hepatic and intestinal CYP3A activity, indinavir had no effect on methadone N-demethylation and clearance, suggesting little or no role for CYP3A in clinical disposition of single-dose methadone. Inhibition of gastrointestinal transporter activity had no influence of methadone bioavailability.

Perioperative pharmacokinetics of methadone in adolescents

BACKGROUND

Methadone is frequently administered to adults experiencing anesthesia and receiving pain treatment. Methadone pharmacokinetics in adults are well characterized, including the perioperative period. Methadone is also used in children. There is, however, no information on methadone pharmacokinetics in children of any age. The purpose of this investigation was to determine the pharmacokinetics of intravenous methadone in children undergoing surgery. Perioperative opioid-sparing effects were also assessed.

METHODS

Eligible subjects were children 5-18 yr undergoing general anesthesia and surgery, with an anticipated postoperative inpatient stay exceeding 3 days. Three groups of 10 to 11 patients each received intravenous methadone hydrochloride after anesthetic induction in ascending dose groups of 0.1, 0.2, and 0.3 mg/kg (up to 20 mg). Anesthetic care was not otherwise changed. Venous blood was obtained for 4 days, for stereoselective determination of methadone and metabolites. Pain assessments were made each morning. Daily and total opioid consumption was determined. Perioperative opioid consumption and pain was determined in a second cohort, which was matched to age, sex, race, ethnicity, surgical procedure, and length of stay, but not receiving methadone.

RESULTS

The final methadone study cohort was 31 adolescents (14 ± 2 yr, range 10-18) undergoing major spine surgery for a diagnosis of scoliosis. Methadone pharmacokinetics were linear over the dose range 0.1-0.3 mg/kg. Disposition was stereoselective. Methadone administration did not dose-dependently affect postoperative pain scores, and did not dose-dependently decrease daily or total postoperative opioid consumption in spinal fusion patients.

CONCLUSIONS

Methadone enantiomer disposition in adolescents undergoing surgery was similar to that in healthy adults.

[Prevention of postoperative hyperalgesia]

Three types of hyperalgesia can occur during the postoperative period: primary hyperalgesia, which disappears with wound healing, secondary or central hyperalgesia, which can lead to chronic pain, and opiate-induced hyperalgesia. Different drugs, most of which are NMDA receptors antagonists, are used to decrease or prevent the risk of central or opiate-induced hyperalgesia. However, it is difficult to determine whether they are really effective and at which dosage: the results of most published studies are difficult to interpret because of methodological problems. The two most frequent of those are: absence of objective measurement of secondary hyperalgesia and difficulties targeting an at risk population.