d-morphine, but not l-morphine, has low micromolar affinity for the non-competitive N-methyl-D-aspartate site in rat forebrain. Possible clinical implications for the management of neuropathic pain

Strategies for Developing κ Opioid Receptor Agonists for the Treatment of Pain with Fewer Side Effects

There is significant need to find effective, nonaddictive pain medications. κ Opioid receptor (KOPr) agonists have been studied for decades but have recently received increased attention because of their analgesic effects and lack of abuse potential. However, a range of side effects have limited the clinical development of these drugs. There are several strategies currently used to develop safer and more effective KOPr agonists. These strategies include identifying G-protein-biased agonists, developing peripherally restricted KOPr agonists without centrally mediated side effects, and developing mixed opioid agonists, which target multiple receptors at specific ratios to balance side-effect profiles and reduce tolerance. Here, we review the latest developments in research related to KOPr agonists for the treatment of pain. SIGNIFICANCE STATEMENT: This review discusses strategies for developing safer κ opioid receptor (KOPr) agonists with therapeutic potential for the treatment of pain. Although one strategy is to modify selective KOPr agonists to create peripherally restricted or G-protein-biased structures, another approach is to combine KOPr agonists with μ, δ, or nociceptin opioid receptor activation to obtain mixed opioid receptor agonists, therefore negating the adverse effects and retaining the therapeutic effect.

Members of the same pharmacological family are not alike: Different opioids, different consequences, hope for the opioid crisis?

Pain management is the specialized medical practice of modulating pain perception and thus easing the suffering and improving the life quality of individuals suffering from painful conditions. Since this requires the modulation of the activity of endogenous systems involved in pain perception, and given the large role that the opioidergic system plays in pain perception, opioids are currently the most effective pain treatment available and are likely to remain relevant for the foreseeable future. This contributes to the rise in opioid use, misuse, and overdose death, which is currently characterized by public health officials in the United States as an epidemic. Historically, the majority of preclinical rodent studies were focused on morphine. This has resulted in our understanding of opioids in general being highly biased by our knowledge of morphine specifically. However, recent in vitro studies suggest that direct extrapolation of research findings from morphine to other opioids is likely to be flawed. Notably, these studies suggest that different opioid analgesics (opioid agonists) engage different downstream signaling effects within the cell, despite binding to and activating the same receptors. This recognition implies that, in contrast to the historical status quo, different opioids cannot be made equivalent by merely dose adjustment. Notably, even at equianalgesic doses, different opioids could result in different beneficial and risk outcomes. In order to foster further translational research regarding drug-specific differences among opioids, here we review basic research elucidating differences among opioids in pharmacokinetics, pharmacodynamics, their capacity for second messenger pathway activation, and their interactions with the immune system and the dopamine D2 receptors.

Levorphanol use: past, present and future

Levorphanol is a potent opioid analgesic that was first approved for use in the United States in 1953. Levorphanol is approved for use in moderate to severe pain where an opioid analgesic is appropriate. Levorphanol has a wide range of activities including mu opioid agonism, delta agonism, kappa1 and kappa3 receptor agonism, N-methyl-d-aspartate receptor antagonism and reuptake inhibition of both norepinephrine and serotonin. This multimodal profile might prove effective for pain syndromes that are refractory to other opioid analgesics, such as central and neuropathic pain and opioid-induced hyperalgesia. Levorphanol is well suited as a first-line opioid and can also be used during opioid rotation. It has no known effect on the cardiac QT interval or drug-drug interactions involving hepatic cytochrome P450s enzymes. In these regards, levorphanol may offer a superior safety profile over methadone and other long-acting opioids. Despite its prospective value of multiple mechanisms of action and the potential for treating various types of pain, levorphanol use has been largely supplanted by other recently approved opioids. Its waning use over the years has caused it to be referred to as the "Forgotten Opioid" and resulted in what some consider its underutilization. In fact, levorphanol is relatively unfamiliar to most prescribers. The purpose of this review is to inform practitioners about the attributes of this opioid and reintroduce it to clinicians as an option for treating moderate to severe pain when alternative treatment options are inadequate, not indicated or contraindicated.

Is levorphanol a better option than methadone?

BACKGROUND

Methadone has been a stalwart pharmacologic option for the management of opioid drug dependence for many years. It substitutes for opioid agonists and possesses certain pharmacokinetic properties that confer characteristics preferable to those of other opioids for this application. Methadone is likewise used as an option for the treatment of pain, particularly chronic pain. It has a spectrum of pharmacodynamic activity, including contributions from non-opioid components, that translates to its specific clinical attributes as an analgesic. Unfortunately, basic science studies and accumulated clinical experience with methadone have revealed some undesirable, and even worrisome, features, including issues of safety. The benefit/risk ratio of methadone might be acceptable if there was no better alternative, but neither its pharmacokinetic nor pharmacodynamic properties are unique to methadone.

OBJECTIVE

We review the basic and clinical pharmacology of methadone and suggest that levorphanol should receive attention as a possible alternative.

CONCLUSION

Unlike methadone, levorphanol is a more potent NMDA antagonist, possesses a higher affinity for DOR and KOR, has a shorter plasma half-life yet longer duration of action, has no CYP450 interactions or QTc prolongation risk, can be a viable option in the elderly, palliative care, and SCI patients, requires little to no need for co-administration of adjuvant analgesics, and has potentially a lower risk of drug-related Emergency Department visits compared to other opioids.

Buprenorphine for Cancer Pain

Buprenorphine (BUP) is a semisynthetic derivative of the opium alkaloid thebaine found in the poppy Papaver somniferum. Its chemical structure contains the morphine structure but differs by having a cyclopropylmethyl group. Buprenorphine is a potent µ opioid agonist. Buprenorphine undergoes extensive first-pass metabolism in the liver and gut. The development of a transdermal BUP formulation in 2001 led to its evaluation in cancer pain. This article provides the practitioner with an update on the current role of BUP in cancer care. It highlights data suggesting effectiveness in various types of cancer pain. The article reviews pharmacology, routes of administration, adverse effects, drug interactions, and cost considerations.

Uliginosin B, a natural phloroglucinol derivative, presents a multimediated antinociceptive effect in mice

Objective

Investigate the involvement of monoaminergic and glutamatergic systems on the antinociceptive and ataxic effects of uliginosin B, which we have already demonstrated to be a promising molecular scaffold to develop new analgesic drugs.

Methods

Uliginosin B was obtained from hexane extract of aerial parts of Hypericum polyanthemum by chromatographic methods. Uliginosin B antinociceptive and motor coordination effects were evaluated in mice by using hot-plate (15 and 90 mg/kg, i.p.) and rotarod (90 mg/kg, i.p.) tests, respectively. The mechanism of action was investigated through pretreatments with prazosin 1 mg/kg intraperitoneal (α1 receptor antagonist), yohimbine 5 mg/kg intraperitoneal (α2 receptor antagonist), pCPA 300 mg/kg intraperitoneal (serotonin synthesis inhibitor) and MK-801 0.25 mg/kg intraperitoneal (N-methyl-D-aspartic acid receptor antagonist).

Key findings

The antinociceptive effect of uliginosin B (15 and 90 mg/kg, i.p.) was reduced significantly by pCPA and MK-801. Prazosin and yohimbine improved the antinociceptive effect of the highest dose (90 mg/kg, i.p.) of uliginosin B only. The ataxic effect of uliginosin B (90 mg/kg, i.p.) was completely prevented by pretreatment with pCPA or MK-801, but it was unaffected by pretreatment with prazosin or yohimbine.

Conclusion

These data confirm the contribution of monoaminergic neurotransmission as well as provide the first evidence of glutamatergic neurotransmission contribution to the uliginosin B effects.

Levorphanol: revisiting an underutilized analgesic

Levorphanol (levo-3-hydroxy-N-methylmorphinan) is a step 3 opioid first developed in the 1940s as an alternative to morphine. Levorphanol belongs to the morphinan opioid series. Levorphanol has greater potency than morphine and is a potent N-methyl-d aspartate (NMDA) antagonist. Levorphanol interferes with the uptake of norepinephrine and serotonin, which makes it potentially useful for neuropathic pain. Glucuronidation changes Levorphanol to Levorphanol-3-glucuronide with excretion by the kidney. Levorphanol has a long half-life and may accumulate with repeated dosing. Levorphanol can be administered orally, intravenously, and subcutaneously. This article provides an update regarding the pharmacodynamics, pharmacology, and clinical efficacy of this often overlooked step 3 opioid.

Preliminary pharmacological evaluation of enantiomeric morphinans

A series of levo- and dextromorphinan pairs have been synthesized and evaluated for their affinities to the mu, kappa, and delta opioid receptors, the N-methyl-D-aspartate (NMDA) channel, and sigma 1 and 2 receptors. It was found that levo isomers tended to have higher affinities at the opioid receptors and moderate to high affinities to the NMDA and sigma receptors, while dextro isomers tended to have lower affinities to the opioid receptors but comparatively higher affinities to the NMDA and sigma receptors. This series of compounds have interesting and complex pharmacological profiles, and merit further investigation as potential therapies for drug abuse treatment.

Medication pain management in the elderly: unique and underutilized analgesic treatment options

BACKGROUND

By 2030, the US population of adults aged ≥65 years will increase by >80%, and these adults will account for nearly 20% of the US population. In this population, the decline of multiple physiologic processes and diseases collectively influence treatment options. Physiologic changes, drug-drug interactions resulting from polypharmacy, and drug-disease interactions combine to make elderly patients more sensitive to the adverse events (AEs) associated with medications, all of which must be considered in drug selection.

OBJECTIVE

This article focuses on select underutilized medication options for analgesia that may provide significant advantages in the elderly population above and beyond commonly prescribed conventional choices.

METHODS

We performed a complete review of the literature using the search terms pain management, elderly, opioids, NSAIDs, topical NSAIDs, levorphanol, buprenorphine transdermal, and tapentadol. Databases searched included PubMed, Google Scholar, Ovid, and Athens. Package inserts were utilized for approval dates, indications, and formulations available. We looked at reviews of agents to identify important studies for consideration that searches may have missed. Pharmacology and pharmacokinetic data were taken from randomized trials focusing in this area. Pivotal Phase III trials were utilized for discussion of clinical trial experience and to summarize efficacy and AEs. For purposes of validity, only peer-reviewed literature was included.

RESULTS

There were limited data that specifically outlined analgesic drug selection and highlighted safer alternatives for the elderly patient based on polypharmacy risks, end-organ deterioration, and/or drug choices that presented less risk. We focused on unique opioid alternatives: levorphanol, which offers several therapeutic advantages similar to methadone but without the pharmacokinetic and drug-interaction pitfalls associated with methadone; tapentadol, associated with significantly less gastrointestinal distress and constipation; and transdermal buprenorphine, an agonist/antagonist with less risk for the toxicities associated with conventional opioids and with compliance benefits. Topical NSAIDs are discussed as a viable therapeutic option. Specific attention to a more desirable tolerability profile, including avoidance of drug interactions, end-organ dysfunction, and gastrointestinal bleed with topical NSAID agents versus their oral counterparts is discussed, including the ability to achieve superior tissue levels for appropriately selected inflammatory conditions.

CONCLUSION

It is incumbent that providers consider these options as part of an analgesic armamentarium in an effort to maximize therapeutic benefit and minimize risks in the increasing elderly patient population.

Chronic methadone treatment shows a better cost/benefit ratio than chronic morphine in mice

Chronic treatment of pain with opiate drugs can lead to analgesic tolerance and drug dependence. Although all opiate drugs can promote tolerance and dependence in practice, the severity of those unwanted side effects differs depending on the drug used. Although each opiate drug has its own unique set of pharmacological profiles, methadone is the only clinically used opioid drug that produces substantial receptor endocytosis at analgesic doses. Here, we examined whether moderate doses of methadone carry any benefits over chronic use of equianalgesic morphine, the prototypical opioid. Our data show that chronic administration of methadone produces significantly less analgesic tolerance than morphine. Furthermore, we found significantly reduced precipitated withdrawal symptoms after chronic methadone treatment than after chronic morphine treatment. Finally, using a novel animal model with a degrading μ-opioid receptor we showed that, although endocytosis seems to protect against tolerance development, endocytosis followed by receptor degradation produces a rapid onset of analgesic tolerance to methadone. Together, these data indicated that opioid drugs that promote receptor endocytosis and recycling, such as methadone, may be a better choice for chronic pain treatment than morphine and its derivatives that do not.

Activation of µ-opioid receptors and block of Kir3 potassium channels and NMDA receptor conductance by L- and D-methadone in rat locus coeruleus

BACKGROUND AND PURPOSE

Methadone activates opioid receptors to increase a potassium conductance mediated by G-protein-coupled, inwardly rectifying, potassium (K(IR) 3) channels. Methadone also blocks K(IR) 3 channels and N-methyl-D-aspartic acid (NMDA) receptors. However, the concentration dependence and stereospecificity of receptor activation and channel blockade by methadone on single neurons has not been characterized.

EXPERIMENTAL APPROACH

Intracellular and whole-cell recording were made from locus coeruleus neurons in brain slices and the activation of µ-opioid receptors and blockade of K(IR) 3 and NMDA channels with L- and D-methadone was examined.

KEY RESULTS

The potency of L-methadone, measured by the amplitude of hyperpolarization was 16.5-fold higher than with D-methadone. A maximum hyperpolarization was caused by both enantiomers (∼30 mV); however, the maximum outward current measured with whole-cell voltage-clamp recording was smaller than the current induced by [Met](5) enkephalin. The K(IR) 3 conductance induced by activation of α(2) -adrenoceptors was decreased with high concentrations of L- and D-methadone (10-30 µM). In addition, methadone blocked the resting inward rectifying conductance (K(IR) ). Both L- and D-methadone blocked the NMDA receptor-dependent current. The block of NMDA receptor-dependent current was voltage-dependent suggesting that methadone acted as a channel blocker.

CONCLUSIONS AND IMPLICATIONS

Methadone activated µ-opioid receptors at low concentrations in a stereospecific manner. K(IR) 3 and NMDA receptor channel block was not stereospecific and required substantially higher concentrations. The separation in the concentration range suggests that the activation of µ-opioid receptors rather than the channel blocking properties mediate both the therapeutic and toxic actions of methadone.

Role of active metabolites in the use of opioids

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

Use of Anesthetic Agents in Neonates and Young Children

BACKGROUND

Some drugs used for sedation and anesthesia produce histopathologic central nervous system changes in juvenile animal models. These observations have raised concerns regarding the use of these drugs in pediatric patients. We summarized the findings in developing animals and describe the steps that the Food and Drug Administration (FDA) and others are taking to assess potential risks in pediatric patients. The FDA views this communication as opening a dialog with the anesthesia community to address this issue.

METHODS

We reviewed the available animal studies literature examining the potential neurotoxic effects of commonly used anesthetic drugs on the developing brain. The search strategy involved crossing the keywords neurotoxic and neuroapoptosis with the following general and specific terms: anesthetic, N-methyl-d-aspartate (NMDA), ketamine, midazolam, lorazepam, fentanyl, methadone, morphine, meperidine, isoflurane, nitrous oxide, sevoflurane, halothane, enflurane, desflurane, propofol, etomidate, barbiturate, methoxyflurane, and chloral hydrate. We summarized several studies sponsored by the FDA in rats and monkeys, initially examining the potential for ketamine, as a prototypical agent, to induce neurodegeneration in the developing brain.

RESULTS

Numerous animal studies in rodents indicate that NMDA receptor antagonists, including ketamine, induce neurodegeneration in the developing brain. The effects of ketamine are dose dependent. The data suggest that limiting exposure limits the potential for neurodegeneration. There is also evidence that other general anesthetics, such as isoflurane, can induce neurodegeneration in rodent models, which may be exacerbated by concurrent administration of midazolam or nitrous oxide. There are very few studies that have examined the potential functional consequences of the neurodegeneration noted in the animal models. However, the studies that have been reported suggest subtle, but prolonged, behavioral changes in rodents. Although the doses and durations of ketamine exposure that resulted in neurodegeneration were slightly larger than those used in the clinical setting, those associated with isoflurane were not. There are insufficient human data to either support or refute the clinical applicability of these findings.

CONCLUSIONS

Animal studies suggest that neurodegeneration, with possible cognitive sequelae, is a potential long-term risk of anesthetics in neonatal and young pediatric patients. The existing nonclinical data implicate not only NMDA-receptor antagonists, but also drugs that potentiate gamma-aminobutyric acid signal transduction, as potentially neurotoxic to the developing brain. The potential for the combination of drugs that have activity at both receptor systems or that can induce more or less neurotoxicity is not clear; however, recent nonclinical data suggest that some combinations may be more neurotoxic than the individual components. The lack of information to date precludes the ability to designate any one anesthetic agent or regimen as safer than any other. Ongoing studies in juvenile animals should provide additional information regarding the risks. The FDA anticipates working with the anesthesia community and pharmaceutical industry to develop strategies for further assessing the safety of anesthetics in neonates and young children, and for providing data to guide clinicians in making the most informed decisions possible when choosing anesthetic regimens for their pediatric patients.

Levorphanol: the forgotten opioid

BACKGROUND

Levorphanol (levo-3-hydroxy-N-methylmorphinan) is a strong opioid that is the only available opioid agonist of the morphinan series. Levorphanol was originally synthesized as a pharmacological alternative to morphine more than 40 years ago. It is considered a step-3 opioid by the World Health Organization (WHO) and has a greater potency than morphine. Analgesia produced by levorphanol is mediated via its interactions with mu, delta, and kappa opioid receptors. Levorphanol is also an N-methyl-D-aspartate (NMDA) receptor antagonist. There is evidence that levorphanol may inhibit uptake of norepinephrine and serotonin. Similar to morphine, levorphanol undergoes glucuronidation in the liver, and the glucuronidated products are excreted in the kidney. Levorphanol can be given orally, intravenously, and subcutaneously.

OBJECTIVE

This article reviews the pharmacodynamics, pharmacology, and clinical efficacy for this often overlooked step-3 opioid.

CONCLUSION

The long half-life of the drug increases the potential for drug accumulation. Levorphanol has clinical efficacy in neuropathic pain.

Pharmacologic Treatment of Central Post-Stroke Pain

OBJECTIVES

Almost 100 years after the first report of the thalamic syndrome, the scientific basis for the treatment of central post-stroke pain (CPSP) is remarkably small. Therefore, the authors aimed to provide evidence-based recommendations for the treatment of CPSP.

METHODS

The authors performed a systematic review of the literature on the pharmacologic treatment of CPSP. All studies and case series were included and evaluated according to their level of evidence. Only CPSP was considered, not other types of central pain.

RESULTS

Amitriptyline and lamotrigine are the only oral drugs proven to be effective in the treatment of CPSP in a placebo-controlled study. IV drugs such as lidocaine, propofol, and ketamine have shown efficacy for short-term control of CPSP, but their application and potential side effects make them unsuitable for long-term treatment. The novel antiepileptic drug gabapentin has been reported to control CPSP in a few patients.

CONCLUSIONS

Amitriptyline, lamotrigine, and gabapentin provide a more favorable efficacy and safety profile than the classic antiepileptic drugs carbamazepine and phenytoin, for which no placebo-controlled evidence of efficacy was found. Clinical trials are urgently needed to optimize pharmacologic treatment of CPSP.

Methadone increases intracellular calcium in SH-SY5Y and SH-EP1-hα7 cells by activating neuronal nicotinic acetylcholine receptors

(-)-Methadone acts as an agonist at opioid receptors. Both (+)- and (-)-enantiomers of methadone have been suggested to be potent non-competitive antagonists of alpha3beta4 neuronal nicotinic acetylcholine receptors (nAChRs). In the present study, we have examined interactions of methadone with nAChRs by using receptor binding assays, patch-clamp recording and calcium fluorometry imaging with SH-SY5Y cells naturally expressing alpha7 and alpha3* nAChR subtypes and SH-EP1-halpha7 cells heterologously expressing human alpha7 nAChRs. Methadone potently inhibited binding of [3H]methyllycaconitine to alpha7 nAChRs and that of [3H]epibatidine to alpha3* nAChRs. Methadone pretreatment induced up-regulation of epibatidine binding sites in SH-SY5Y cells. Using whole-cell patch-clamp recording, both isomers of methadone activated cation currents via mecamylamine-sensitive nAChRs in SH-SY5Y cells. Nicotine and both (+)- and (-)-methadone evoked increases in [Ca2+]i in both fluo-3AM loaded cell lines, and these effects were blocked by mecamylamine and by the alpha7 selective antagonist methyllycaconitine, suggesting effects of methadone as alpha7-nAChR agonist. Sensitivity of sustained nicotine and methadone effects to blockade by CdCl2, ryanodine and xestospongin-c implicates voltage-operated Ca2+ channels and intracellular Ca2+ stores as downstream modulators of elevated [Ca2+]i. Collectively, our results suggest that methadone engages in complex and potentially pharmacologically significant interactions with nAChRs.

Effects of nociceptin/orphanin FQ and endomorphin-1 on glutamate and GABA release, intracellular [Ca2+] and cell excitability in primary cultures of rat cortical neurons

The effects of nociceptin/orphanin FQ (N/OFQ) and endomorphin-1 (EM-1) on glutamate and GABA release, intracellular calcium, neuronal excitability and glutamate current were investigated in rat primary cortical neuronal cultures. Through their specific receptors N/OFQ and EM-1 (0.02-1 microM) inhibited the electrically evoked outflow of [3H]D-aspartate at most to -50% and that of [3H]GABA to -30%. In addition, at 1 microM, both peptides induced a decrease of the firing rate caused by electrical depolarization. N/OFQ 1-10 microM did not influence either the electrically evoked calcium influx or the glutamate-evoked currents, whereas EM-1 1 microM significantly inhibited them. Thus, in cortical neurons in culture, both N/OFQ and EM-1 inhibited the secretory process and neuronal excitability but EM-1 also affected calcium influx and cell body responsiveness to glutamate. Consequently, EM-1 appeared to dampen this excitatory signal more then N/OFQ did.

Functional inhibition by methadone of N-methyl-D-aspartate receptors expressed in Xenopus oocytes: stereospecific and subunit effects

Methadone is a strong opioid analgesic that is finding increasing use in chronic pain therapeutics. We explored its reported efficacy for inhibiting N-methyl-D-aspartate (NMDA) receptors in a functional electrophysiologic assay (Xenopus laevis oocyte expression). Racemic methadone inhibited all subtypes of rat NMDA receptors with derived 50% inhibitory concentrations in the low micromolar range. These concentrations overlap with clinically achievable concentrations reported in pharmacokinetic studies. In contrast, morphine inhibited these functional ion channels only at 8-16 times larger concentrations. The NR1/2A and NR1/2B subtype combinations were in general significantly more sensitive to inhibition by methadone and morphine compared with the NR1/2C and NR1/2D subtypes. In the presence of racemic methadone, the maximum NMDA-stimulated currents were markedly decreased, but the NMDA concentration producing 50% of maximal activation was altered only slightly, indicating that methadone blocks by a noncompetitive mechanism. Although stereoisomers of methadone showed minimal stereoselectivity in most subtypes, R(-) methadone was highly selective in its inhibition of the NR1/2A combination. These results provide further functional data describing the NMDA receptor inhibitory actions of methadone and support the hypothesis that methadone acts through both opioid and NMDA receptor mechanisms.

IMPLICATIONS

At clinically achievable concentrations, methadone inhibits functional N-methyl-D-aspartate receptors. These results indicate a unique mode of action by this opioid that may enhance its ability to treat chronic pain and to limit opioid tolerance.

Low-dose methadone has an analgesic effect in neuropathic pain: a double-blind randomized controlled crossover trial

The analgesic effectiveness and adverse effect incidence of a daily dose of 10 or 20 mg of oral methadone were evaluated in 18 patients with a diverse range of chronic neuropathic pain syndromes, who had all responded poorly to traditional analgesic regimens. Analgesia was seen after each dose of methadone. As compared with placebo, the 20 mg daily dose (given as 10 mg bd) resulted in statistically significant (P = 0.013-0.020) improvements in patient Visual Analogue Scale ratings of maximum pain intensity, average pain intensity and pain relief, recorded at the same time daily. The analgesic effects extended over 48 hours, as shown by statistically significant (P = 0.013-0.020) improvements in all three outcomes on the rest days instituted between each daily dose. Analgesic effects (lowered maximum pain intensity and increased pain relief, on the day of dosing only) were also seen when the lower daily dose of 10 mg methadone (given as 5 mg bd) was used, but these failed to reach statistical significance (P = 0.064 and 0.065, respectively). Interpatient analysis showed that the analgesic effects were not restricted to any particular type of neuropathic pain. Patient compliance was high throughout the trial. One patient withdrew during the 10 mg and six during the 20 mg methadone treatment periods. This is the first double-blind randomized controlled trial to demonstrate that methadone has an analgesic effect in neuropathic pain.

Monitor: molecules and profiles

Monitor provides an insight into the latest developments in drug discovery through brief synopses of recent presentations and publications together with expert commentaries on the latest technologies. There are two sections: Molecules summarizes the chemistry and the pharmacological significance and biological relevance of new molecules reported in the literature and on the conference scene; Profiles offers commentary on promising lines of research, emerging molecular targets, novel technology, advances in synthetic and separation techniques and legislative issues.