Plasma concentrations of methadone during postoperative patient-controlled extradural analgesia

Methadone: applications in pediatric anesthesiology and critical care medicine

Like morphine, methadone is a pure agonist at the µ opioid receptor. However, in distinction to morphine which has an elimination half-life of 2-3 h, methadone has an elimination half-life of 24-36 h. In addition to its effects at the µ opioid receptor, methadone is an antagonist at the N-methyl-D-aspartate (NMDA) receptor and also inhibits the reuptake of the neurotransmitters, serotonin and norepinephrine, in the central nervous system. Given its long half-life and high oral bioavailability, methadone has had a primary role in the outpatient treatment of patients with a history of opioid abuse or addiction. However, its unique pharmacology and cellular effects make it a valuable agent in the treatment of both acute and chronic pain of various etiologies. The following manuscript reviews the pharmacologic properties of methadone and discusses its clinical applications in the practice of pediatric anesthesiology and pediatric critical care medicine.

Safe and Appropriate Use of Methadone in Hospice and Palliative Care: Expert Consensus White Paper

Methadone has several unique characteristics that make it an attractive option for pain relief in serious illness, but the safety of methadone has been called into question after reports of a disproportionate increase in opioid-induced deaths in recent years. The American Pain Society, College on Problems of Drug Dependence, and the Heart Rhythm Society collaborated to issue guidelines on best practices to maximize methadone safety and efficacy, but guidelines for the end-of-life scenario have not yet been developed. A panel of 15 interprofessional hospice and palliative care experts from the U.S. and Canada convened in February 2015 to evaluate the American Pain Society methadone recommendations for applicability in the hospice and palliative care setting. The goal was to develop guidelines for safe and effective management of methadone therapy in hospice and palliative care. This article represents the consensus opinion of the hospice and palliative care experts for methadone use at end of life, including guidance on appropriate candidates for methadone, detail in dosing, titration, and monitoring of patients' response to methadone therapy.

The management of pain in children with life-limiting illnesses

The management of pain in children with life-limiting illnesses is complex and unfortunately not often done effectively. Pain is a multidimensional symptom that can overshadow all other experiences of both the child and family. This article focuses on topics common to practitioners caring for children with lifelimiting illnesses, including a review of myths and obstacles to achieving adequate pain control, a review of the pathophysiology of pain, an overview of the use of opioids in children, an approach to the management of neuropathic pain, and a brief discussion of nonpharmacologic pain management strategies.

A comparison of extradural and intravenous methadone on intraoperative isoflurane and postoperative analgesia requirements in dogs

OBJECTIVE

To compare the effects of intravenous (IV) and extradural (ED) methadone on end-tidal isoflurane concentration (Fe'ISO) and postoperative analgesic requirements in dogs undergoing femoro-tibial joint surgery.

STUDY DESIGN

Randomized, blinded, clinical study. Animals Twenty-four healthy client-owned dogs undergoing surgical repair of ruptured cruciate ligaments.

METHODS

Dogs were randomly assigned to two groups of 12 animals and received either ED or IV methadone (0.3 mg kg(-1) diluted with saline to 0.2 mL kg(-1)). Pre-anaesthetic medication was IV acepromazine (0.05 mg kg(-1)). Anaesthesia was induced with propofol and maintained initially with an Fe'ISO of 1.0% delivered in oxygen. Methadone was injected with the dogs in sternal recumbency; the observer was unaware of the administration route. At 10 minutes (stimulation 1) and 20 minutes (stimulation 2) after methadone administration pelvic limb reflexes were tested by digit-clamping. The time at skin incision (stimulation 3), joint-capsule incision (stimulation 4), tibial tuberosity drilling (stimulation 5), fabellar suturing (stimulation 6) and extracapsular tightening (stimulation 7) were noted. Changes in heart rate (HR) and respiratory rate and arterial blood pressure associated with surgery were recorded along with the corresponding Fe'ISO. After 20 minutes of anaesthesia, Fe'ISO was decreased to the minimum required to maintain stable anaesthesia. Immediately after tracheal extubation, 1, 2, 3 and 6 hours postoperatively and on the morning after surgery, the degree of pain present was assessed using a numerical rating scale. The HR, respiratory rates and blood pressure were also recorded at these times. Serum cortisol and blood glucose concentrations were measured before pre-anaesthetic medication and at each postoperative pain scoring interval except at 1 and 2 hours. Ketoprofen (2 mg kg(-1)), carprofen (4 mg kg(-1)) or meloxicam (0.2 mg kg(-1)) were given by subcutaneous injection whenever pain scoring indicated moderate discomfort was present.

RESULTS

Controlled ventilation was required in six dogs which stopped breathing after IV methadone. The median Fe'ISO at stimulus 5 was 1.0% in the IV and 0.83% in the ED group. At stimulus 6, Fe'ISO was 1.0% in the IV and 0.8% in the ED group; the difference was statistically significant (p </= 0.05). There was no significant difference in the duration of postoperative analgesia associated with administration route.

CONCLUSIONS

Extradural methadone significantly reduces the isoflurane requirement compared with IV methadone during femoro-tibial joint surgery in dogs.

CLINICAL RELEVANCE

Extradural methadone provides safe and effective pain relief in dogs undergoing cruciate ligament repair.

A Qualitative Systematic Review of the Role of N-Methyl-d-Aspartate Receptor Antagonists in Preventive Analgesia

We evaluated in a qualitative systematic review the effect of N-methyl-D-aspartate (NMDA) receptor antagonists on reducing postoperative pain and analgesic consumption beyond the clinical duration of action of the target drug (preventive analgesia). Randomized trials examining the use of an NMDA antagonist in the perioperative period were sought by using a MEDLINE (1966-2003) and EMBASE (1985-2003) search. Reference sections of relevant articles were reviewed, and additional articles were obtained if they evaluated postoperative analgesia after the administration of NMDA antagonists. The primary outcome was a reduction in pain, analgesic consumption, or both in a time period beyond five half-lives of the drug under examination. Secondary outcomes included time to first analgesic request and adverse effects. Forty articles met the inclusion criteria (24 ketamine, 12 dextromethorphan, and 4 magnesium). The evidence in favor of preventive analgesia was strongest in the case of dextromethorphan and ketamine, with 67% and 58%, respectively, of studies demonstrating a reduction in pain, analgesic consumption, or both beyond the clinical duration of action of the drug concerned. None of the four studies examining magnesium demonstrated preventive analgesia.

IMPLICATIONS

We evaluated, in a qualitative systematic review, the effect of N-methyl D-aspartate antagonists on reducing postoperative pain and analgesic consumption beyond the clinical duration of action of the target drug (preventive analgesia). Dextromethorphan and ketamine were found to have significant immediate and preventive analgesic benefit in 67% and 58% of studies, respectively.

Drug interactions with patient-controlled analgesia

Patient-controlled analgesia (PCA) has become standard procedure in the clinical treatment of pain. Its widespread use in patients with all kinds of diseases opens a variety of possible interactions between analgesics used for PCA and other drugs that might be administered concomitantly to the patient. Many of these drug interactions are of little clinical importance. However, some drug interactions have been reported to result in serious clinical problems. Drug interactions can either predominantly affect the pharmacokinetics or pharmacodynamics of the drug. Most important pharmacokinetic drug interactions occur at the level of drug metabolism or protein binding. Acceleration of methadone metabolism caused by cytochrome P450 (CYP) 3A4 induction by antiretroviral drugs or rifampicin (rifampin) has caused methadone withdrawal symptoms. Lack of morphine formation from codeine as a result of CYP2D6 inhibition by quinidine results in an almost complete loss of the analgesic effects of codeine. Alterations of methadone protein binding caused by an inhibition of alpha1-acid glycoprotein synthesis by alkylating substances are another possibility for predominantly pharmacokinetically based drug interactions during PCA. Furthermore, inhibition of P-glycoprotein by anticancer drugs could result in altered transmembrane transport of morphine, methadone or fentanyl, although this has not been shown to be of clinical relevance. Synergistic effects of systemically administered opioids with spinally or topically delivered opioids or anaesthetics have been reported frequently. The same is true for the opioid-sparing effects of coadministered non-opioid analgesics. Antidepressants, anticonvulsants or alpha2-adrenoreceptor agonists have also been shown to exert additive analgesic effects when administered together with an opioid. Inconsistent findings, however, are reported regarding the treatment of patients with opioid-induced nausea and sedation, since coadministration of antiemetics either increased or decreased the respective adverse effects or revealed additional unwanted drug effects.

Continuous epidural infusion of racemic methadone results in effective postoperative analgesia and low plasma concentrations

PURPOSE

To compare two protocols of epidural administration of racemic methadone for postoperative analgesia (continuous infusion and intermittent bolus), focussing on plasma concentration, analgesic efficacy and side effects.

METHODS

Ninety patients undergoing abdominal or lower-limb surgery were randomly assigned to two groups in a prospective double-blind design. The continuous infusion patients (n=60) received initial doses of 3 to 6 mg followed by 6 to 12 mg by continuous infusion over 24 hr. The bolus administration patients (n=30) received repeated boluses of 3 to 6 mg of racemic methadone every eight hours. Pain intensity was assessed on a visual analog scale. Amount of supplementary analgesia was recorded, as was the incidence of side effects. Plasma methadone concentrations were determined by high performance liquid chromatography. Treatment was continued for 72 hr.

RESULTS

Pain relief was good and comparable in both groups throughout the three days of treatment. No accumulation of plasma racemic methadone was observed in either group, although the concentrations were significantly higher in the bolus group. Miosis was significantly more frequent in the bolus group.

CONCLUSION

Plasma methadone concentrations were significantly lower with continuous infusion. Plasma methadone accumulation, which is considered the main disadvantage for its purported influence on the incidence of side effects, did not occur at the doses used over the three days of treatment that we report.

Methadone is safe for treating hospitalized patients with severe pain

PURPOSE

Methadone is still regarded as a second line opioid for patients suffering from severe pain, and is rarely used in hospitalized patients. The infrequent use of methadone is probably due to its long plasma half-life that could lead to accumulation and toxicity. In the present study we report that clinically effective analgesic doses of methadone, given either epidurally or orally, can be used safely for prolonged treatment in hospitalized patients.

CLINICAL FEATURES

Over a five-year period we administered methadone at Hadassah Hospital in Jerusalem to 3,954 in-patients with severe pain, 12% of whom were younger than 17 yr. Satisfactory pain relief was recorded in more than 85% of the patients. None of the patients treated with oral methadone developed serious side effects. Three patients, treated with epidural methadone (0.09%), developed a clinically significant respiratory depression. In all three cases, epidural pump failure or pump misprogramming resulted in methadone overdose. None of the children or adults treated with methadone developed addiction during hospitalization.

CONCLUSION

Based on its analgesic properties and marked safety profile, we suggest that methadone could be added to the analgesic armamentarium of in-hospital health-care providers. Moreover, methadone could serve as the opioid of first choice in some in-patient populations.

Side-effects of epidural infusions of opioid bupivacaine mixtures

The incidence of side-effects occurring with epidural diamorphine (0.05 mg.ml-1), fentanyl (2.0 micrograms.ml-1), methadone (0.1 mg.ml-1), morphine (0.05 mg.ml-1) and pethidine (1.0 mg.ml-1) used by infusion in combination with bupivacaine has been compared. One hundred and sixty patients were studied, 32 receiving each opioid. The incidence of nausea and vomiting was significantly greater with morphine than fentanyl (p = 0.0097) and pethidine (p = 0.0021). The incidence of pruritus was significantly greater with morphine and diamorphine than with methadone (p = 0.012) and pethidine (p = 0.027). Morphine was also associated with a significantly greater incidence of urinary retention than pethidine (p = 0.012) and methadone (p = 0.025).

Efficacy of intra-muscular analgesics for acute pain in sheep

The analgesic action of intramuscularly injected buprenorphine, methadone, flunixin meglumine and xylazine was examined in sheep, using algesimetry based on a leg withdrawal response to an electrical stimulus. No analgesic response was detected for buprenorphine, methadone or flunixin meglumine. Only the alpha 2-adrenoceptor agonist, xylazine, produced an analgesic response. The current required to elicit a response increased by 170% (4.5 +/- 0.43 mA to 12.23 +/- 1.14 mA; mean +/- SE) after a dose of 0.05 mg/kg xylazine; by 180% (4.73 +/- 0.3 mA to 13.28 +/- 2.35 mA) after 0.1 mg/kg and by 510% (4.52 +/- 0.29 mA to 27.63 +/- 3.89 mA) after 0.2 mg/kg. Intramuscular xylazine appears to be an effective analgesic agent for acute pain in the sheep and further investigation into ideal administration regimens and dosage may provide more detailed information on relationships between dose, analgesic and sedative effects. The findings also suggest that some common analgesic agents, and opioids in particular, may be ineffective for the management of acute pain in sheep and that any analgesic should be administered only on the basis of its proven efficacy in that species.

Comparison of epidural methadone with epidural diamorphine for analgesia following caesarean section

Analgesia provided by either 5 mg diamorphine, or 5 mg methadone administered by the epidural route during elective caesarean section was compared in 40 women. The median time to further analgesia in the methadone group was 395 min, and 720 min in the diamorphine group, P = 0.0003. Linear analogue scores to assess pain were measured 2-hourly for 12 h, then again at 24 h postoperatively. Pain scores were significantly lower in the diamorphine group at 8 and 10 h. The median cumulative i.m. morphine dose administered during the first 24 h was 20 mg in the methadone group and 0 mg in the diamorphine group (P = 0.0005). Nausea and pruritus were common side effects in both groups. Continuous pulse oximetry data were available for 12 h post-operatively in 15 patients receiving methadone, and in 17 patients receiving diamorphine. One or more episodes of significant desaturation (< 90% for 30 s), occurred in three patients receiving methadone, and in nine patients receiving diamorphine. Desaturation to 90-92% occurred in a further three patients given epidural diamorphine, and in one further patient given epidural methadone.