Opioid poorly-responsive cancer pain. Part 2: basic mechanisms that could shift dose response for analgesia

Methadone in the madness: a case series and review of methadone management in hospital settings

The management of patients on chronic methadone therapy for opioid use disorder presents unique pharmacological and psychosocial challenges in hospital settings. This case series discusses complexities such as methadone's variable pharmacokinetics, alternatives to oral methadone and conversion ratios. Additionally, it outlines the nuances around the psychosocial considerations of methadone therapy and addressing addiction-related behaviors without compromising patient dignity. The review calls for individualized care plans with uninterrupted opioid agonist therapy to meet the baseline opioid requirements and pro-active pain management plans. Enhanced clinician education and better real-world data to guide methadone management is important to improve outcomes for this vulnerable patient cohort.

Monoclonal antibody targeting mu-opioid receptor attenuates morphine tolerance via enhancing morphine-induced receptor endocytosis

Morphine is a frequently used analgesic that activates the mu-opioid receptor (MOR), which has prominent side effects of tolerance. Although the inefficiency of morphine in inducing the endocytosis of MOR underlies the development of morphine tolerance, currently, there is no effective therapy to treat morphine tolerance. In the current study, we aimed to develop a monoclonal antibody (mAb) precisely targeting MOR and to determine its therapeutic efficacy on morphine tolerance and the underlying molecular mechanisms. We successfully prepared a mAb targeting MOR, named 3A5C7, by hybridoma technique using a strategy of deoxyribonucleic acid immunization combined with cell immunization, and identified it as an immunoglobulin G mAb with high specificity and affinity for MOR and binding ability to antigens with spatial conformation. Treatment of two cell lines, HEK293T and SH-SY5Y, with 3A5C7 enhanced morphine-induced MOR endocytosis via a G protein-coupled receptor kinase 2 (GRK2)/β-arrestin2-dependent mechanism, as demonstrated by immunofluorescence staining, flow cytometry, Western blotting, coimmunoprecipitation, and small interfering ribonucleic acid (siRNA)-based knockdown. This mAb also allowed MOR recycling from cytoplasm to plasma membrane and attenuated morphine-induced phosphorylation of MOR. We established an in vitro morphine tolerance model using differentiated SH-SY5Y cells induced by retinoic acid. Western blot, enzyme-linked immunosorbent assays, and siRNA-based knockdown revealed that 3A5C7 mAb diminished hyperactivation of adenylate cyclase, the in vitro biomarker of morphine tolerance, via the GRK2/β-arrestin2 pathway. Furthermore, in vivo hotplate test demonstrated that chronic intrathecal administration of 3A5C7 significantly alleviated morphine tolerance in mice, and withdrawal jumping test revealed that both chronic and acute 3A5C7 intrathecal administration attenuated morphine dependence. Finally, intrathecal electroporation of silencing short hairpin RNA illustrated that the in vivo anti-tolerance and anti-dependence efficacy of 3A5C7 was mediated by enhanced morphine-induced MOR endocytosis via GRK2/β-arrestin2 pathway. Collectively, our study provided a therapeutic mAb, 3A5C7, targeting MOR to treat morphine tolerance, mediated by enhancing morphine-induced MOR endocytosis. The mAb 3A5C7 demonstrates promising translational value to treat clinical morphine tolerance.

Acupuncture alleviates acute peritonitis: A case report

Many inflammatory and infectious entities can affect the peritoneum acutely, and patients with peritonitis often have painful expressions. Abdominal pain can be aggravated by coughing, breathing, and turning the body. Here we report the case of an 88-year-old patient with acute gastrointestinal perforation. The patient has been experiencing pain in the right lower abdomen, presenting persistent colic. The X-ray of abdomen and abdominal computed tomography showed perforation of digestive tract. In addition to the use of anti-infection and stomach protection agents, we use different analgesic injections, but the effect on reducing the pain was not obvious. After acupuncture treatment, the patient quickly relieved the pain of acute peritonitis in 1 minute. However, to our knowledge, there is few literature showing that acupuncture relieves preoperative opioid-induced hyperalgesia in patients with acute peritonitis. Based on this case, we suggest acupuncture as an option in the management of relieving the pain of acute peritonitis when opioid therapy is ineffective.

When the game is hard, more complex weapons are needed

OBJECTIVES

The aim of this paper is to illustrate how to manage a very difficult pain condition.

METHODS

This is a clinical note of a complex approach using multiple analgesic regimens to effectively afford challenging pain situations.

RESULTS

A man underwent an opioid dose titration, followed by dose stabilisation for some months. Then he underwent two opioid substitutions, unsuccessfully. A spinal analgesia provided good analgesia for a prolonged period of time, necessitating variable interventions to counteract the evolving, challenging clinical situation.

CONCLUSIONS

The description of this case illustrates the need of a high level of experience and knowledge to elaborate complex strategies step by step every time the pain syndrome was worsening. Recommendations are unlikely in these extreme circumstances, and treatment should be based on continuous clinical counteraction to the evolving clinical conditions.

A Practical Approach to Acute Postoperative Pain Management in Chronic Pain Patients

In the United States, more than 100 million people suffer from chronic pain. Among patients presenting for surgery, about one in four have chronic pain. Acute perioperative pain management in this population is challenging because many patients with chronic pain require long-term opioids for the management of this pain, which may result in tolerance, physical dependence, addiction, and opioid-induced hyperalgesia. These challenges are compounded by the ongoing opioid epidemic that has resulted in calls for a reduction in opioid use, with a concurrent increase in the number of patients with chronic opioid exposure presenting for surgery. This article aims to summarize practical considerations for acute postoperative pain management in patients with chronic pain conditions. A patient-centered acute pain management plan, including nonopioid analgesics, regional anesthesia, and careful selection of opioid medications, can lead to adequate analgesia and satisfaction with care. Also, a meticulous rotation from one opioid to another may decrease opioid requirement, increase analgesic effectiveness, and improve satisfaction with care.

Critical Care Pain Management in Patients Affected by the Opioid Epidemic: A Review

The rapid rise in the opioid epidemic has had a deleterious impact across the United States. This increase has drawn the attention of the critical care community not only because of the surge in acute opioid overdose-related admissions, but also due to the increase in the number of opioid-dependent and opioid-tolerant patients being treated in the intensive care unit (ICU). Opioid-related issues relevant to the critical care physician include direct care of patients with opioid overdoses, the provision of sufficient analgesia to patients with opioid dependence and tolerance, and the task of preventing long-term opioid dependence in patients who survive ICU care. This review identifies the challenges facing the ICU physician working with patients presenting with opioid-related complications, discusses current solutions, and suggests future areas of research and heightened ICU clinician attention.

Opioid Rotation to Methadone for Refractory Cancer Pain: A Case Series

Methadone has been increasingly used in the treatment of refractory cancer pain with different conversion methods and ratios described.A retrospective chart review of patients on methadone for cancer pain was conducted to assess its use as the primary opioid, focusing on pain characteristics, opioid rotation indication, previous analgesics, adverse effects and final methadone dose in comparison with the pre-rotation Morphine Equivalent Daily Dose (MEDD).Eight patients were rotated to methadone due to refractory moderate-severe cancer pain and achieved good pain relief. Three developed adverse effects (2 mild, 1 serious). None required withdrawal of methadone. The final methadone dose required varied significantly from predictions made based on equianalgesic conversion tables.Methadone is effective for the treatment of refractory cancer pain. The eventual required methadone doses for these patients were significantly different from predicted doses suggested by equianalgesic conversion tables and guidelines. This highlights the importance of individualized titration and careful clinical assessment during the rotation and in the days after, to prevent serious adverse effects.

Opioid-Induced Tolerance and Hyperalgesia

Opioids are very potent and efficacious drugs, traditionally used for both acute and chronic pain conditions. However, the use of opioids is frequently associated with the occurrence of adverse effects or clinical problems. Other than adverse effects and dependence, the development of tolerance is a significant problem, as it requires increased opioid drug doses to achieve the same effect. Mechanisms of opioid tolerance include drug-induced adaptations or allostatic changes at the cellular, circuitry, and system levels. Dose escalation in long-term opioid therapy might cause opioid-induced hyperalgesia (OIH), which is a state of hypersensitivity to painful stimuli associated with opioid therapy, resulting in exacerbation of pain sensation rather than relief of pain. Various strategies may provide extra-opioid analgesia. There are drugs that may produce independent analgesic effects. A tailored treatment provided by skilled personnel, in accordance with the individual condition, is mandatory. Any treatment aimed at reducing opioid consumption may be indicated in these circumstances. Interventional techniques able to decrease the pain input may allow a decrease in the opioid dose, thus reverting the mechanisms producing tolerance of OIH. Intrathecal therapy with local anesthetics and a sympathetic block are the most common techniques utilized in these circumstances.

Comprehensive Perioperative Management Considerations in Patients Taking Methadone

PURPOSE OF REVIEW

Well-informed staff can help decrease risks and common misconceptions regarding opioid-tolerant patients, especially those taking methadone.

RECENT FINDINGS

In 2015, opioid pain relievers were the second most used drug at 3.8 million. Overdose death was three times greater in 2015 than in 2000. Medication-assisted treatment was sought by more than 2 million individuals with substance use disorder, one of which is methadone. Chronic pain affects millions of adults in the USA. Opioid therapy is widely used among these adults. Related to the risk of abuse and dependence, guidelines suggest that opioid therapy may not be considered first-line treatment. A multidisciplinary approach, including thorough preoperative evaluation, the utilization of multimodal pain management strategies, and opioid-sparing techniques in both the intraoperative and postoperative periods will allow for the best possible outcome.

The Patient with Difficult Cancer Pain

Most patients with cancer pain can be managed with relatively simple methods using oral analgesics at relatively low doses, even for prolonged periods of time. However, in some clinical conditions pain may be more difficult to manage. Various factors can interfere with a desirable and favorable analgesic response. Data from several studies assessing factors of negative pain prognosis have indicated that neuropathic pain, incident pain, psychological distress, opioid addiction, and baseline pain intensity were associated with more difficult pain control. In this narrative review, the main factors that make the therapeutic response to opioids difficult are examined.

Palliative Pain Management: When Both Pain and Suffering Hurt

Patients with advanced cancer frequently experience intractable pain without sufficient response to a conventional pharmacological approach. One reason for refractory pain at the end of life can be the bidirectional nature of pain and suffering. Three terminally ill patients were assessed using a multidimensional palliative pain concept, including sensory, affective, cognitive, and existential components. In these patients, resistant pain did not equal insufficient eradication of the nociceptive input, but also suffering. Unrelieved emotions, depressive or anxious symptoms, delirium, difficulties communicating, or chemical coping influenced the expression of pain, illuminating the phenomenon of somatization. Palliative pain treatment integrated analgesic treatments, psychological, rehabilitative, and existential interventions, in consideration of individual expectations and outcomes. With the disciplined assessment and alternative multidisciplinary palliative approach, the quality of life of three terminally ill cancer patients with intractable pain could be enhanced, and unnecessary interventions and escalation of medications avoided.

Efficacy and Safety of Oxycodone Injection for Relieving Cancer Pain: A Study in Japan Consisting of Two Open Trials for Intravenous and Subcutaneous Administration

Pure oxycodone injection became increasingly necessary after oral oxycodone was launched in Japan in 2003. However, trials clarifying the efficacy and safety of injection are rare. Therefore, a multicenter open study on injection was designed and carried out in 2010, resulting in the launch of injection therapy in 2012. As published domestic case reports on efficacy already show widespread prescription, this study aimed to provide useful information for cancer pain relief in Japan and other countries. Our oxycodone injection study consisted of two trials, one of intravenous (S#9131) and the other of subcutaneous (S#9132) administration. The minimum required number of enrolled patients suffering cancer pain was determined to be 70 in S#9131 and 20 in S#9132. These studies had the same dose-titration protocol as the main endpoint, i.e., pain relief rate (PRR) defined as the rate of achieving adequate pain control (APC), as in prior oral oxycodone trials in Japan. In S#9131, PRR was 81.4% (95% confidence interval: 70.3-89.7%), therefore, the null hypothesis of PRR<70% was rejected using the binominal one-sided test (p=0.0217). In S#9132, PRR was 73.7% also surpassing 70%. Safety was also assessed in the same way as in prior trials. The majority of adverse effects were moderate or mild and recovered with no sequelae. As shown above, the injection was considered to be effective and safe in cancer pain treatment. The details of these trials, particularly the dose-titration protocol for achieving APC and route switching information, are expected to enhance injection convenience for prescribers.

The switch from buprenorphine to tapentadol: is it worth?

Opioid analgesia continues to be the primary pharmacologic intervention for managing acute pain and malignant pain in both hospitalized and ambulatory patients. The increasing use of opioids in chronic nonmalignant pain is more problematic. Opioid treatment is complicated with the risks raised by adverse effects, especially cognitive disturbance, respiratory depression but also the risk of tolerance, opioid abuse and drug-disease interactions. Despite the growing number of available opioids within the last years, adequate trials of opioid rotation are lacking and most of the information is anecdotal. This article reviews the clinical evidence surrounding the switch from transdermal buprenorphine to tapentadol in malignant and non-malignant pain. Tapentadol acts on both the μ-opioid receptors (MOR) and on the neuronal reuptake of noradrenaline with a limited usefulness in acute pain management while buprenorphine is a mixed agonist-antagonist, and both present some advantages over other opioids. Both drugs show particular pharmacodynamic and pharmacokinetic properties which reduce the risks of development of tolerance, opioid abuse, diversion and determine fewer hormone changes than the "classical opioids" making these opioids more attractive than other opioids in long term opioid treatment. However, in the absence of powered clinical trials, the evidence to support the method used for transdermal buprenorphine rotation to tapentadol is weak.

Hyperalgesia and opioid switching

Opioids, intended to abolish pain, can unexpectedly produce hyperalgesia, particularly during rapid opioid escalation. Opioid switching could be a therapeutic option in a condition of opioid-induced tolerance or hyperalgesia, but conversion ratios between opioids are difficult to apply in this context and require strict surveillance and expertise.

This situation is challenging, because the rapid escalation of opioid doses, possibly due to the development of opioid-induced tolerance, can cause hyperalgesia. To avoid this adverse effect, clinicians need to refine their assessment of pain treatment and consider opioid switching. The authors present a case report in which switching from fentanyl to methadone was effective in a patient who developed hyperalgesia as a consequence of a rapid opioid escalation. Regardless of the expected clinical improvement of opioid switching using lower doses of the second opioid, the final dose of the second opioid was exaggeratedly low, probably as a consequence of the disappearance of hyperalgesia induced by the first opioid.

The results of this case and others like it may help practitioners develop a meaningful approach during opioid escalation, possibly anticipating the need for opioid switching or other alternative measures for patients with uncontrolled cancer pain.

Opioid-induced hyperalgesia: when pain killers make pain worse

A 44-year-old woman had a temporal glioma and was admitted to the hospice with pain that was not controlled despite escalating opioids. Her pain levels rose after every dose increase resulting now in continuous pain, making her very low in mood. Her short-term memory had also declined in a stepwise fashion with each increase in opioids. Additionally, her poor health had had a detrimental effect on family life. Physical examination was difficult due to allodynia but no major abnormality was found. The team suspected opioid-induced hyperalgesia and decided to cut the patient's opioids by one-third initially. This immediately improved the overall pain. The opioids continued to be decreased incrementally every 1-2 days until the pain had disappeared completely. She was stabilised on a dose almost one-seventh of her original regime. Mood and memory also improved as opioids decreased and she was discharged home after 8 days.

Opioid-induced hyperalgesia and tolerance: understanding opioid side effects

Opioid-induced pain or opioid tolerance should be considered when opioid therapy fails to provide expected analgesic effects or when there is unexplainable pain exacerbation following opioid treatment. As a result, an increase in the opioid dosage may not be the solution to ineffective opioid therapy for chronic pain management. A decrease in the opioid mass may actually provide pain relief in many instances. At one time, it was anticipated that opioid-induced pain was related to upregulation of NMDA receptors with a downregulation of mu receptors. However, there is growing evidence to suggest the opioid receptor-based hyperalgesic mechanism may be directly modulated by the NMDA receptor. Furthermore, the mechanism that causes opioid tolerance may be the same mechanism that causes opioid-induced pain. Current evidence suggests that opioid-induced pain sensitivity could be prevented by interrupting the cellular and molecular changes associated with the development of opioid tolerance. Continued research may lead the way to a new period in which patients prone to opioid-induced pain could be identified, allowing one to tailor pharmacologic pain therapy to each patient.

The use of very-low-dose methadone for palliative pain control and the prevention of opioid hyperalgesia

BACKGROUND

Opioid dose escalation may cause hyperalgesia, mediated by the N-methyl-D-aspartate (NMDA) pathway. Methadone is an atypical opioid that inhibits hyperalgesia through NMDA-blockade, especially at low doses.

OBJECTIVE

To evaluate the efficacy of using very-low-dose methadone as the sole long-acting opioid agent in a hospice practice.

DESIGN

A retrospective, observational study of the use of methadone, ≤15 mg daily, with as-needed short-acting opiates. Adjuvant nonopioid medications included haloperidol, which may have NMDA-blocking effects.

SETTING/SUBJECTS

We reviewed the records of 240 patients admitted to a community-based hospice from July 1, 2011 to April 1, 2012, with data collected until hospice discharge or until April 30, 2012.

MEASUREMENTS

Descriptive statistics were used to summarize patient demographics, medication regimens, and reported pain scores measured on a numeric rating scale from 0 to 10.

RESULTS

All patients received short-acting opiates, in a morphine-equivalent dose of 5 mg every 4 hours as needed, while 40% also received methadone at a median daily dose of 5 mg. Of those on methadone, almost half received scheduled haloperidol. The population had a median reported pain score of 0 and a peak score of 3, with similar results seen for cancer and noncancer groups. Two-thirds of patients never reported a pain score greater than 3.

CONCLUSION

The use of very-low-dose methadone in conjunction with adjuvant haloperidol resulted in excellent pain control without dose escalation or opioid-induced hyperalgesia, for both cancer and noncancer diseases. We conclude that low-dose methadone should be part of first-line treatment in palliative pain management.

The effect of age on opioid switching to methadone: a systematic review

BACKGROUND

The aim of this review was to assess from the existing literature the effect of age on the outcome of opioid switching to methadone, and the possible influence on conversions ratios.

DISCUSSION

Older patients represent a challenge for physicians, as a further factor may play a role in dosing methadone and possibly on successful switching. Although existing data are not conclusive because this aspect did not receive particular attention in most studies, at the present time age has not been found to be independently associated with the dose ratio. Further prospective studies in a large sample of patients, subgrouped for classes of age, opioid doses, and reasons to switch, should be designed to provide more information.

Conversion ratios for opioid switching in the treatment of cancer pain: a systematic review

In this paper we describe the results of a systematic search of the literature on conversion ratios during opioid switching. This is part of a project of the European Palliative Care Research Collaboration to update the European Association for Palliative Care recommendations for the use of opioid analgesics in the treatment of cancer pain. Studies were eligible for inclusion if they involved adult patients with chronic cancer pain, contained data on opioid conversion ratios, were prospective and were written in English. Thirty-one studies were identified and included. The majority of the studies had methodological flaws and were not designed to explore or demonstrate equianalgesic dose data. However, the data allow some recommendations to be made that could be helpful to clinicians for whom there are few reliable experimental data on which to base dosing guidelines. Switching to transdermal fentanyl (TDfe) or buprenorphine (TDbu) is an option for patients with stable, controlled pain. Reliable and consistent studies show a ratio of 100 : 1 between oral morphine (ORmo) and TDfe. A ratio of 75 : 1 between ORmo and TDbu may be appropriate, but the supporting evidence here is much less robust. Data are relatively consistent to support a conversion ratio between ORmo and oral hydromorphone (ORhy) of 5 : 1. Despite some limitations, there is evidence to support the use of an approximate conversion ratio of ORmo:oral oxycodone (ORox) of 1.5 : 1. The conversion between ORox and ORhy is estimated to be 1 : 4. When switching from different opioids to methadone the conversion ratio is highly variable, ranging from 5 : 1 to 10 : 1 and much higher in some studies. The derived ratios are influenced by several factors, including the reasons for switching and previous opioid doses. An individual treatment decision and strict monitoring is recommended for patients considered at risk.

Combined catechol-O-methyltransferase and mu-opioid receptor gene polymorphisms affect morphine postoperative analgesia and central side effects

BACKGROUND

Previous studies have generated controversial results regarding the influence of the genetic variations of μ-opioid receptors on morphine analgesia and opioid-related side effects in the postoperative period. Few studies have been conducted attempting to assess the combined effects of variation within ≥2 genes in relation to morphine response. In this study, we investigated whether combined catechol-O-methyltransferase and μ-opioid receptor polymorphisms contribute to the morphine response in postoperative analgesia.

METHODS

One hundred two surgical patients were enrolled in this prospective, observational study. All patients received general anesthesia and were screened for μ-opioid receptor polymorphism A118G (Asn40Asp) and catechol-O-methyltransferase G1947A (Val158Met) polymorphism using a blood sample of DNA. Patient-controlled analgesia was provided postoperatively and morphine consumption was observed. Any pain at rest or side effects were measured with rating scales.

RESULTS

The heterozygous patients with μ-opioid receptor A118G and catechol-O-methyltransferase G1947A mutation consumed significantly less morphine in the postanesthetic recovery room and 48 hours after surgery compared with homozygous patients of the A118 variant. Nausea and sedation scores were also significantly lower during all observed postoperative periods for heterozygous patients and only 2 patients (18%) from this group received antinausea treatment.

CONCLUSION

This study has demonstrated the importance of the gene-gene approach in understanding the morphine response in patients after lower abdominal surgery. More studies are needed to characterize the combined effects of multiple genes and demographic as well as clinical variables in predicting the correct morphine dosage and corresponding opioid-related side effects.

Frequency, indications, outcomes, and predictive factors of opioid switching in an acute palliative care unit

The aim of this study was to prospectively evaluate the frequency, indications, outcomes, and predictive factors associated with opioid switching, using a protocol that had been clinically applied and viewed as effective for many years. A prospective study was carried out on a cohort of consecutive cancer patients who were receiving opioids but had an unacceptable balance between analgesia and adverse effects, despite symptomatic treatment of side effects. The initial conversion ratio between opioids and routes was as follows (mg/day): oral morphine 100=intravenous morphine 33=transdermal fentanyl 1=intravenous fentanyl 1=oral methadone 20=intravenous methadone 16=oral oxycodone 70=transdermal buprenorphine 1.3. The switch was assisted by opioids used as needed, and doses were changed after the initial conversion according to clinical response in an acute care setting. Intensity of pain and symptoms associated with opioid therapy were recorded. A distress score (DS) was calculated as a sum of symptom intensity. A switch was considered successful when the intensity of pain and/or DS, or the principal symptom necessitating the switch, decreased to at least 33% of the value recorded before switching. One hundred eighteen patients underwent opioid substitutions. The indications for opioid switching were uncontrolled pain and adverse effects (50.8%), adverse effects (28.8%), uncontrolled pain (15.2%), and convenience (4.2%). Overall, 103 substitutions were successful. Ninety-six substitutions were successful after the first switching, and a further substitution was successful in seven patients who did not respond to the first switch. The mean time to achieve dose stabilization after switching was 3.2 days. The presence of both poor pain control and adverse effects was related to unsuccessful switching (P<0.004). No relationship was identified between unsuccessful switching and the opioid dose, opioid sequence, pain mechanism, or use of adjuvant medications. Opioid switching was an effective method to improve the balance between analgesia and adverse effects in more than 80% of cancer patients with a poor response to an opioid. The presence of both poor pain relief and adverse effects is a negative factor for switching prognosis, whereas renal failure is not.

Too Much of a Good Thing? Treating the Emerging Syndrome of Opioid-Induced Hyperalgesia

Pain is the primary reason individuals seek health care, and chronic pain is the leading cause of disability. Patients with chronic pain often require treatment with strong analgesics, including opioids. Mounting evidence shows that very high opioid doses or rapidly escalating doses may lead to a paradoxical syndrome of increasing pain that is nonresponsive to opioid therapy. A review of the published literature describing the phenomenon of opioid-induced hyperalgesia was conducted, and management strategies were reviewed. A systematic search of PubMed using Medical Subject Headings terms to narrow search criteria identified 3 treatment strategies. The strategies evaluated in this literature review include opioid rotation, coadministration of N-methyl-D-aspartate receptor antagonists, and coadministration of opioid antagonists. Further research is needed to draw conclusive recommendations. As of now, the safest and most effective treatment strategy showing the best evidence involves the use of opioid rotation.

Morphine treatment accelerates sarcoma-induced bone pain, bone loss, and spontaneous fracture in a murine model of bone cancer

Metastatic bone cancer causes severe pain that is primarily treated with opioids. A model of bone cancer pain in which the progression of cancer pain and bone destruction is tightly controlled was used to evaluate the effects of sustained morphine treatment. In cancer-treated mice, morphine enhanced, rather than diminished, spontaneous, and evoked pain; these effects were dose-dependent and naloxone-sensitive. SP and CGRP positive DRG cells did not differ between sarcoma or control mice, but were increased following morphine in both groups. Morphine increased ATF-3 expression only in DRG cells of sarcoma mice. Morphine did not alter tumor growth in vitro or tumor burden in vivo but accelerated sarcoma-induced bone destruction and doubled the incidence of spontaneous fracture in a dose- and naloxone-sensitive manner. Morphine increased osteoclast activity and upregulated IL-1 beta within the femurs of sarcoma-treated mice suggesting enhancement of sarcoma-induced osteolysis. These results indicate that sustained morphine increases pain, osteolysis, bone loss, and spontaneous fracture, as well as markers of neuronal damage in DRG cells and expression of pro-inflammatory cytokines. Morphine treatment may result in "add-on" mechanisms of pain beyond those engaged by sarcoma alone. While it is not known whether the present findings in this model of osteolytic sarcoma will generalize to other cancers or opioids, the data suggest a need for increased understanding of neurobiological consequences of prolonged opioid exposure which may allow improvements in the use of opiates in the effective management of cancer pain.

Opioid switching: a systematic and critical review

Cancer patients with pain may not respond to increasing doses of opioids because they develop adverse effects before achieving an acceptable analgesia, or the analgesic response is poor, despite a rapid dose escalation. Opioid switching may significantly improve the balance between analgesia and adverse effects. We conducted a systematic review of existing literature on opioid switching. According to available data, opioid switching results in clinical improvement in more than 50% of patients with chronic pain with poor response to one opioid. However, data are based on open studies or small case series. Reasons for switching may influence the dose of the alternative drug. Opioid conversion should not be a mere mathematical calculation, but just a part of a more comprehensive evaluation of pain, adverse effect intensity, comorbidities, and concomitant drugs. The process of reaching an optimal dose should be highly individualized, particularly when patients are switched from high doses of opioids, given the wide conversion ratios reported in literature.

Addition of a second opioid may improve opioid response in cancer pain: preliminary data

Recent experimental data suggest a possible use of an opioid combination to improve analgesia. In cancer patients, a rapid opioid escalation due to either worsening of the pain condition or the development of tolerance is a critical phase, as this condition is associated with a negative prognosis. The aim of this study was to assess the effects of adding a second opioid at low doses in patients with a poor analgesic benefit after dose escalation. Fourteen patients receiving strong opioids who had increased their dosage more than 100% in the last week unsuccessfully were randomly chosen to add a second opioid to the first using an initial equivalent dosage of 20% of the previous therapy. The dose of the second opioid was then changed according to the clinical situation to obtain an acceptable pain control with minimal adverse effects. Pain and symptoms associated with opioid therapy were assessed, and an opioid escalation index (OEI) was calculated at weekly intervals. OEI significantly decreased after adding the second opioid, and this trend was also maintained for the following weeks. Similarly, pain intensity was significantly improved and maintained at acceptable levels for the following weeks. The second opioid did not induce significant opioid-related adverse effects. The opioid combination was able to break opioid escalation in patients with pain syndromes with a poor response to the previous opioid. It allowed for a regaining of analgesia, regardless of the opioid combination used. These preliminary observations should be confirmed in further studies.

Intravenous fentanyl for cancer pain: a "fast titration" protocol for the emergency room

Patients with cancer sometimes are admitted to the emergency room due to severe pain. Despite the fact that morphine's hydrophilicity can delay its peak effects after intravenous administration up to 30 minutes, it is still the most commonly used opioid during cancer pain emergencies. Fentanyl is a synthetic, lipophilic opioid, more potent than morphine, and achieves peak effects after intravenous administration in 5 minutes. According to our observations, intravenous fentanyl could be safely used in the emergency room to treat patients who need fast titration of an opioid to control their pain. In our study, fentanyl was employed in a four-step protocol to treat patients admitted to our palliative care emergency room due to severe pain, regardless of the previous use of morphine at home. Titration with intravenous fentanyl was successfully employed in 18/18 (100%) of patients, with an average time for pain control at about 11 minutes, and without relevant adverse effects. We conclude that intravenous fentanyl could be safely used for severe cancer pain when rapid titration is being considered.

Hyperalgesia: an emerging iatrogenic syndrome

Clinical reports suggest that opioids, intended to abolish pain, can unexpectedly produce hyperalgesia. This paradoxical effect may be mechanistically related to tolerance induced by increasing doses of opioids. Two case reports illustrate a syndrome characterized by increasing pain pursued by escalating opioid doses, which results in a worsening of the clinical picture. Several experimental data may help explain the course of this challenging clinical condition. In escalating opioid doses rapidly, a risk of opioid-induced hyperalgesia should be recognized, as higher doses of opioids may stimulate rather than inhibit the central nervous system by different mechanisms. Alternative procedures should be taken into consideration to break this cycle, should it occur. More data are needed to detect this condition, as currently no diagnostic information on specific markers, clinical or biochemical, exists.

Medication-focused approach to total pain: poor symptom control, polypharmacy, and adverse reactions

Neuropathic pain, known to have poor opioid response, can be difficult to control. Although several classes of adjuvant medications are believed to be of benefit in managing neuropathic pain, they have potential side effects that occasionally outweigh their benefits. The psychospiritual suffering of patients with advanced cancer may heighten the distress associated with physical symptoms. If undiagnosed, this may lead to increases in dose and the number of medications administered in the hope of better symptom control. This case report describes the successful interdisciplinary management of an advanced cancer patient whose multiple drug therapy had added to rather than alleviated his distress by causing more side effects than symptom relief.

Adjuvant ketamine analgesia for the management of cancer pain

OBJECTIVE

To review the clinical literature evaluating the utilization of intravenous ketamine for the management of cancer-related pain, to summarize the data that suggest ketamine is an appropriate adjuvant method of providing analgesia and to report a case of successful pain management using ketamine in a patient with recurrent testicular cancer at our institution.

DATA SOURCES

Primary literature was identified through a MEDLINE search (1966-March 2002), and additional information was obtained through secondary and tertiary sources.

DATA SYNTHESIS

The available data suggest that supplementation of morphine with ketamine improves analgesia in patients with cancer, and also provides insight to the controversy regarding the efficacy and adverse effects of various ketamine doses. At subanesthetic doses, ketamine may be beneficial at reducing opioid requirements and related adverse effects.

CASE SUMMARY

A 34-year-old white man with recurrent testicular cancer was admitted with radiating neuropathic pain of the legs and lower back. The patient was suspected to also be experiencing opioid adverse effects; therefore, alternative analgesic options were warranted. Ketamine was successful in reducing patient-reported pain and was also well tolerated.

CONCLUSIONS

Ketamine is an adjuvant analgesic for the treatment of cancer-related pain when other agents either fail or are intolerable. Accordingly, there are several factors that may prevent adequate pain control with opioid use; therefore, alternative analgesic options should be considered. Promise exists for ketamine as a contemporary analgesic in the appropriate patient.

Tumor implantation in mouse humerus evokes movement-related hyperalgesia exceeding that evoked by intramuscular carrageenan

In this paper we compare two innovative models of movement-related pain: tumor-induced nociception following implantation of fibrosarcoma cells into bone and muscle inflammation-induced nociception following injection of the irritant carrageenan into muscle. Importantly, using the grip force test, an assay of movement-related hyperalgesia, both non-malignant and malignant pain are examined in parallel. Movement-related hyperalgesia, known clinically as a specific type of 'breakthrough pain', is a common feature of bone cancer and is thought to be a predictor of poor response to conventional analgesic pharmacotherapy (Bruera et al., 1995, J. Pain Symptom. Manage. 10 (1995) 348; Mercadaute et al., 1992, Pain 50 (1992) 151; Pain 81 (1999) 129). Implantation of NCTC 2472 sarcoma cells in both humeri or injection of carrageenan (4%) in both triceps of C3H/He mice produced apparent forelimb hyperalgesia that was not associated with mechanical hyperalgesia in the forepaw, whereas carrageenan at 6 and 8% did evoke significant cutaneous hyperalgesia of the forepaw as well. Control groups receiving implants of vehicle or no treatment at all did not manifest this forelimb hyperalgesia. B6C3/F1 mice implanted with non-lysis-inducing G3.26 melanoma cells or vehicle did not manifest significant hyperalgesia when compared to B6C3/F1 mice receiving fibrosarcoma cells, indicating a dependence on bone involvement for induction of hyperalgesia in this model. Histological examination at days 3, 7, and 10 post-implantation showed a clear correlation of tumor growth-induced bone destruction with behavioral hyperalgesia. Morphine was more potent in decreasing the maximal hyperalgesia induced by carrageenan than that induced by tumor implantation. Acutely administered morphine (3-100mg/kg, i.p.) attenuated peak hyperalgesia of carrageenan-injected mice (ED(50) 6.9 mg/kg) and tumor-bearing mice (ED(50) 23.9 mg/kg) in a dose-related manner with a difference in potency of 3.5. Tumor-implanted mice with a level of hyperalgesia comparable to that induced by carrageenan required almost three times more morphine (ED(50) 18.5mg/kg) for equivalent attenuation of forelimb hyperalgesia. These animal models of movement-related hyperalgesia may aid in discerning the peripheral and central mechanisms underlying pain that accompanies bone metastases and distinguishing it from the pain associated with muscular inflammation. Importantly, they may also aid in predicting differences in analgesic efficacy in different types of musculoskeletal pain.

Advances in cancer pain management

Although most patients with cancer pain can attain a favorable balance between analgesia and side effects with a conventional approach to opioid therapy, a substantial minority cannot. For these patients, an important subgroup of whom have neuropathic pain, alternative therapeutic strategies are needed. With a detailed assessment, clinicians should be able to choose among the large and diverse group of options available and implement an approach, or combination of approaches, that have a high probability of improving analgesic outcomes.

Opioid poorly-responsive cancer pain. Part 3. Clinical strategies to improve opioid responsiveness

Some pain syndromes may be difficult to treat due to a poor response to opioids. This situation demands a range of alternative measures, including the use of adjuvant drugs with independent effects, such as antidepressants, sodium channel-blocking agents, steroids and anti-inflammatory drugs (NSAIDs); drugs that reduce opioid side effects; and drugs that enhance analgesia produced by opioids, such as N-methyl-D-aspartate (NMDA) antagonists, calcium channel antagonists, and clonidine. Other approaches, including opioid trials, neural blockade when necessary, and psychological interventions, also may be useful.