Opioid responsiveness

Opioid conversion in adults with cancer: MASCC-ASCO-AAHPM-HPNA-NICSO guideline

PURPOSE

To standardize and improve the safety and efficacy of opioid conversion in people with cancer.

METHODS

The Multinational Association of Supportive Care in Cancer (MASCC), American Society of Clinical Oncology (ASCO), American Academy of Hospice and Palliative Medicine (AAHPM), Hospice and Palliative Nurses Association (HPNA), and Network Italiano Cure di Supporto in Oncologia (NICSO) convened an Expert Panel to develop recommendations based on a systematic review of the literature and a formal consensus process. The systematic review focused on randomized and non-randomized studies published from database inception to June 2022. A modified Delphi approach was used to develop and finalize recommendations. Recommendations developed by the Expert Panel underwent two rounds of consensus voting before being finalized.

RESULTS

The systematic review, published separately, identified 208 eligible studies. These studies provided mixed and inclusive findings regarding optimal approaches to opioid conversion. In consensus voting, 58 of 84 statements met or exceeded the required 75% level of agreement and were accepted. This process demonstrated some consistencies in conversion ratios between particular opioids internationally, but also uncovered variability in opioid conversion ratios among experts, particularly for methadone.

RECOMMENDATIONS

The recommendations address three main topics: pre-conversion assessments, strategies for conversion, and post-conversion assessments. The goal is to reduce the relative risk of overdosing or under-dosing opioids when converting from one opioid to another or converting administration routes. The strength of the evidence from the trials is modest, and there are large clinical practice and research gaps. The panel hopes this guideline will establish an international best practice baseline that can be built upon by new research and better-designed trials. Additional information is available at www.asco.org/supportive-care-guidelines .

Methadone for cancer pain: What have we learned from clinical studies?

The analgesic ladder guideline proposed by the World Health Organization has been shown to be effective in controlling cancer pain in about 80 percent of patients, but the remaining 20 percent still experience pain. Several strategies have been used to manage refractory cancer pain and opioid toxicity. Switching opioids, alternative routes of opioid administration, optimizing adjuvants, and invasive procedures are proposed treatments. Extensive medical literature corroborates each one of those treatments. Rotation from one opioid to another is a noninvasive strategy to overcome opioid side effects and refractory pain. Frequently, methadone is used during opioid rotation. However, there is a lack of consensus on how to proceed on rotation from morphine to methadone. In the current era of evidence-based medicine, the medical literature fails to answer some cancer pain-management issues. The purpose of this review is to clarify a process for transitioning from morphine to methadone.

Pain management in trauma: A review study

Background:

Pain in trauma has a role similar to the double-edged sword. On the one hand, pain is a good indicator to determine the severity and type of injury. On the other hand, pain can induce sever complications and it may lead to further deterioration of the patient. Therefore, knowing how to manage pain in trauma patients is an important part of systemic approach in trauma. The aim of this manuscript is to provide information about pain management in trauma in the Emergency Room settings.

Methods:

In this review we searched among electronic and manual documents covering a 15-yr period between 2000 and 2016. Our electronic search included Pub Med, Google scholar, Web of Science, and Cochrane databases. We looked for articles in English and in peer-reviewed journals using the following keywords: acute pain management, trauma, emergency room and injury.

Results:

More than 3200 documents were identified. After screening based on the study inclusion criteria, 560 studies that had direct linkage to the study aim were considered for evaluation based World Health Organization (WHO) pain ladder chart.

Conclusions:

To provide adequate pain management in trauma patients require: adequate assessment of age-specific pharmacologic pain management; identification of adequate analgesic to relieve moderate to severe pain; cognizance of serious adverse effects of pain medications and weighting medications against their benefits, and regularly reassessing patients and reevaluating their pain management regimen. Patient-centered trauma care will also require having knowledge of barriers to pain management and discussing them with the patient and his/her family to identify solutions.

Continuous Intrathecal Infusion of Ziconotide for Treatment of Chronic Malignant and Nonmalignant Pain Over 12 Months: A Prospective, Open-label Study

Objectives.  This study aims to assess the safety and efficacy of long-term intrathecal (IT) ziconotide infusion. Materials and Methods.  In this prospective study, 155 patients with severe chronic pain (48 with malignant pain, 107 with nonmalignant pain) who had been responsive to short-term IT ziconotide in a double-blind, placebo-controlled study received long-term, open-label IT ziconotide monotherapy. Efficacy assessments included the mean percentage change on the visual analog scale of pain intensity from baseline in the study of origin; safety was monitored by adverse event (AE) reports, periodic laboratory tests, and vital sign measurements. Results.  At the last available observation, the visual analog scale of pain intensity scores had decreased by a mean of 36.9% from baseline in the short-term trial (N = 144; 95% CI: 30.1-43.7%; p < 0.0001). The mean IT ziconotide dose remained stable over 12 months in the 31 patients who participated in the study for ≥ one year. Ziconotide-related AEs were reported in 147 out of 155 patients (94.8%); 39.4% of patients discontinued treatment because of AEs, the majority of which were considered ziconotide related. Conclusions.  Ziconotide IT monotherapy provided patients with analgesia for 12 months in this open-label study, with an acceptable benefit/risk profile and no evidence of tolerance.

Effects of acupuncture for cancer pain and quality of life - a case series

BACKGROUND

Many cancer patients seek complementary and alternative medicine (CAM) including acupuncture to manage their cancer-related symptoms or side effects of treatments. Acupuncture is used to manage cancer pain and improve quality of life (QoL). This study aimed to conduct a preliminary study on a case series to evaluate the feasibility of acupuncture for treating cancer pain and to collect preliminary data on the effectiveness of acupuncture in treating cancer pain and improving QoL.

METHODS

A semi-standardized acupuncture treatment comprising one to three treatment sessions (20-30 minutes per session) per week for 8 weeks was provided by four licensed acupuncturists, who had more than 5 years of clinical experience, at the University Health Center. The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C3) and a visual analogue scale (VAS) for pain rating were used as the outcome measures to assess pain and QoL. Data were collected at baseline, immediately after 2, 4, 6, and 8 weeks of treatment and at 4 weeks after treatment completion (week 12).

RESULTS

Two males and five females with a median age of 66 years (range: 44-71 years) completed the study. For the VAS, the percentage of improvement ranged between 18% and 95%. The baseline mean raw score was reduced from 51 mm to 36 mm at the end of week 8 and to 23 mm at the end of week 12. The percentage of overall QoL improvement ranged between 20% and 100%. The mean raw score for QoL improved with time. The baseline score was increased from 55 to 69 at the end of treatment (week 8) and to 73 after the follow-up (week 12).

CONCLUSIONS

This pilot study on a case series showed that acupuncture might be beneficial for reducing pain and improving QoL in cancer patients.

Pharmacokinetic and pharmacodynamic modeling of opioid-induced gastrointestinal side effects in patients receiving tapentadol IR and oxycodone IR

PURPOSE

To understand the relationship between the risk of opioid-related gastrointestinal adverse effects (AEs) and exposure to tapentadol and oxycodone as well as its active metabolite, oxymorphone, using pharmacokinetic/pharmacodynamic models.

METHODS

The analysis was based on a study in patients with moderate-to-severe pain following bunionectomy. Population PK modeling was conducted to estimate population PK parameters for tapentadol, oxycodone, and oxymorphone. Time to AEs was analyzed using Cox proportional-hazards models.

RESULTS

Risk of nausea, vomiting, and constipation significantly increased with exposure to tapentadol or oxycodone/oxymorphone. However, elevated risk per drug exposure of AEs for tapentadol was ~3-4 times lower than that of oxycodone, while elevated AE risk per drug exposure of oxycodone was ~60 times lower than that for oxymorphone, consistent with reported in vitro receptor binding affinities for these compounds. Simulations show that AE incidence following administration of tapentadol IR is lower than that following oxycodone IR intake within the investigated range of analgesic noninferiority dose ratios.

CONCLUSIONS

This PK/PD analysis supports the clinical findings of reduced nausea, vomiting and constipation reported by patients treated with tapentadol, compared to patients treated with oxycodone.

Errors in opioid prescribing: a prospective survey in cancer pain

CONTEXT

Cancer pain is debilitating and has multidimensional consequences. It can be treated adequately in up to 90% of patients by following pain management guidelines. Nevertheless, inadequate pain control remains a global problem.

OBJECTIVES

We surveyed prescribing patterns in patients referred to our Palliative Medicine Program (PMP) to identify common errors in opioid use.

METHODS

Consecutive cancer patients seen by our PMP were prospectively surveyed for the presence of pain and errors in opioid prescribing at the time of initial consultation. Our recommendations to correct and optimize pain management also were recorded.

RESULTS

One hundred eighty-six consecutive cancer patients were screened. One hundred seventeen (63%) had cancer pain, 151 opioid prescribing errors were detected, and 147 different recommendations were made. Most common were failure to order around-the-clock opioids for constant pain, and the failure to treat or prevent opioid side effects. Multiple errors were more common in females, but the sex difference did not reach statistical significance. There was no difference in the errors by pain severity or reason for consultation.

CONCLUSION

Opioid prescribing errors were common. Females may be at greater risk of multiple errors. A PM consultation program is effective in identifying and correcting a wide variety of opioid prescribing errors.

Opioid equianalgesic tables: are they all equally dangerous?

Pain is one of the most common symptoms in cancer patients. Opioids are widely prescribed for this and other purposes. Properly used, they are safe, but they have serious and potentially lethal side effects. Successful use of opioids to manage cancer pain requires adequate knowledge about opioid pharmacology and equianalgesia for the purpose of both drug rotation and route conversion. The aim of this study was to demonstrate variations in equianalgesic ratios, as quoted in equianalgesic tables and various educational materials widely available to practicing physicians. We surveyed commercially available educational materials in package inserts, teaching materials provided by pharmaceutical companies, and the Physicians' Desk Reference for equianalgesic tables of commonly used opioids. We found inconsistent and variable equianalgesic ratios recommended for both opioid rotation and conversion. Multiple factors like inter- and intraindividual differences in opioid pharmacology may influence the accuracy of dose calculations, as does the heterogeneity of study design used to derive equianalgesic ratios. Equianalgesic tables should only serve as a general guideline to estimate equivalent opioid doses. Clinical judgment should be used and individual patient characteristics considered when applying any table. Professional organizations and regulators should establish a rotation and conversion consensus concerning opioid equianalgesic ratios. Systematic research on equianalgesic opioid dose calculation is recommended to avoid adverse public health consequences of incorrect or inappropriate dosing. Current information in equianalgesic tables is confusing for physicians, and dangerous to the public.

Pain therapy

Cancer-related pain is a major issue of healthcare systems worldwide. The reported incidence, considering all stages of the disease, is 51%, which can increase to 74% in the advanced and terminal stages. For advanced cancer, pain is moderate to severe in about 40-50% and very severe or excruciating in 25-30% of cases. Pain is both a sensation and an emotional experience. Pain is always subjective; and may be affected by emotional, social and spiritual components thus it has been defined as "total pain". From a pathophysiological point of view, pain can be classified as nociceptive (somatic and visceral), neuropathic (central, peripheral, sympathetic) idiopathic or psychogenic. A proper pain assessment is fundamental for an effective and individualised treatment. In 1986 the World Health Organisation (WHO) published analgesic guidelines for the treatment of cancer pain based on a three-step ladder and practical recommendations. These guidelines serve as an algorithm for a sequential pharmacological approach to treatment according to the intensity of pain as reported by the patient. The WHO analgesic ladder remains the clinical model for pain therapy. Its clinical application should be employed only after a complete and comprehensive assessment and evaluation based on the needs of each patient. When applying the WHO guidelines, up to 90% of patients can find relief regardless of the settings of care, social and/or cultural environment. This is the standard treatment on a type C basis. Only when such an approach is ineffective are interventions such as spinal administration of opioid analgesics or neuroinvasive procedures recommended.

The cannabinoid receptor agonist, WIN 55, 212-2, attenuates tumor-evoked hyperalgesia through peripheral mechanisms

Several lines of evidence suggest that cannabinoids can attenuate various types of pain and hyperalgesia through peripheral mechanisms. The development of rodent cancer pain models has provided the opportunity to investigate novel approaches to treat this common form of pain. In the present study, we examined the ability of peripherally administered cannabinoids to attenuate tumor-evoked mechanical hyperalgesia in a murine model of cancer pain. Unilateral injection of osteolytic fibrosarcoma cells into and around the calcaneus bone resulted in tumor formation and mechanical hyperalgesia in the injected hindpaw. Mechanical hyperalgesia was defined as an increase in the frequency of paw withdrawals to a suprathreshold von Frey filament (3.4 mN) applied to the plantar surface of the hindpaw. WIN 55, 212-2 (1.5 to 10 microg) injected subcutaneously into the tumor-bearing hindpaw produced a dose-dependent decrease in paw withdrawal frequencies to suprathreshold von Frey filament stimulation. Injection of WIN 55,212-2 (10 microg) into the contralateral hindpaw did not decrease paw withdrawal frequencies in the tumor-bearing hindpaw. Injection of the highest antihyperalgesic dose of WIN 55,212-2 (10 microg) did not produce catalepsy as determined by the bar test. Co-administration of WIN 55,212-2 with either cannabinoid 1 (AM251) or cannabinoid 2 (AM630) receptor antagonists attenuated the antihyperalgesic effects of WIN 55, 212-2. In conclusion, peripherally administered WIN 55,212-2 attenuated tumor-evoked mechanical hyperalgesia by activation of both peripheral cannabinoid 1 and cannabinoid 2 receptors. These results suggest that peripherally-administered cannabinoids may be effective in attenuating cancer pain.

Intrathecal analgesia

Since the first use of intrathecal (IT) drug infusion systems in the early 1980s, these delivery systems have undergone numerous revisions making them more tolerable, easier to program, and longer lasting. Concurrent with technological advances, the indications for IT pump placement have also been continuously evolving, to the point where the most common indication is now noncancer pain. This article provides an evidence-based review of the indications, efficacy, and complications of IT drug therapy for the most commonly administered spinal analgesics.

Gabapentin and an opioid combination versus opioid alone for the management of neuropathic cancer pain: a randomized open trial

Neuropathic cancer pain represents a major challenge. Treatment often requires adjuvant analgesics, including gabapentin, to complement the effects of opioids. This study aimed to compare the effectiveness and safety of gabapentin combined with an opioid versus opioid monotherapy for the management of neuropathic cancer pain. Seventy-five cancer patients who were receiving opioid therapy and reported sufficient pain relief of nociceptive, but not neuropathic, pain were enrolled. Sixty-three patients completed the study. Patients were randomized to one of the following treatment protocols: 1) gabapentin adjuvant to ongoing opioid treatment titrated according to pain response while opioid dose was kept constant (group GO), and 2) continuation of opioid monotherapy according to the World Health Organization treatment ladder approach (group OO). Changes in pain intensity, allodynia, and analgesic drug consumption were evaluated at Day 4 and Day 13. Side effects were also recorded. Both treatments resulted in a significant reduction of pain intensity at Day 4 and Day 13 compared to baseline. However, mean pain intensity for burning and shooting pain was significantly higher in the OO group compared to the GO group at both the fourth (P=0.0001) and 13th (P=0.0001) days of the study. An earlier significant decrease (at Day 4, P=0.002) was observed for allodynia in the GO group compared to the OO group. The rate of side effects in the GO group was significantly lower than that in the OO group (P=0.015). These data suggest that gabapentin added to an opioid provides better relief of neuropathic pain in cancer patients than opioid monotherapy; this combination of gabapentin and an opioid may represent a potential first-line regimen for the management of pain in these patients.

Intrathecal analgesia

Since the first use of intrathecal (IT) drug infusion systems in the early 1980s, these delivery systems have undergone numerous revisions making them more tolerable, easier to program, and longer lasting. Concurrent with technological advances, the indications for IT pump placement have also been continuously evolving, to the point where the most common indication is now noncancer pain. This article provides an evidence-based review of the indications, efficacy, and complications of IT drug therapy for the most commonly administered spinal analgesics.

A Titration Strategy Is Needed To Manage Breakthrough Cancer Pain Effectively: Observations from Data Pooled from Three Clinical Trials

BACKGROUND

Breakthrough pain is a prevalent and serious problem in patients with cancer. However, it is not known how best to predict the effective dose of breakthrough opioid for any given patient.

METHODS

Data were pooled and reanalyzed from three large, randomized clinical trials of the rapidly absorbed oral transmucosal fentanyl citrate lozenges (OTFC) in which patients were carefully titrated to an optimal OTFC dose. The relationships between the optimal OTFC dose, patients' previous opioid dose, 24-hour total opioid, and patient characteristics were explored to determine whether the optimal OTFC dose can be predicted based on pretreatment clinical factors.

RESULTS

The cohort included 188 patients within the three trials whose breakthrough pain was effectively managed with OTFC. Prior to entry into the trial, the average breakthrough opioid dose in the 188 patients was 12% of the daily dose of scheduled opioid but strikingly, ranged from 1%-72%. The optimal OTFC dose was poorly correlated with patients' scheduled or previous breakthrough opioid doses. The only clinically meaningful correlation was that the average final OTFC dose significantly decreased with increasing age. Overall, there was enormous interindividual variability in patients' dose requirements for breakthrough pain.

CONCLUSIONS

This is the largest study to date of the relationship between clinical variables and the effective dose of OTFC when titrated to effect for breakthrough cancer pain. These results suggest that use of breakthrough medication should routinely be individualized with a titration strategy separate from the around-the-clock medication, according to each patient's response to their breakthrough opioid.

Chronic neuropathic pain. Mechanisms, diagnosis, and treatment

BACKGROUND

The management of chronic pain represents a significant public health issue in the United States. It is both costly to our health care system and devastating to the patient's quality of life. The need to improve pain outcomes is reflected by the congressional declaration of the present decade as the "Decade of Pain Control and Research," and the acknowledgment in January 2001 of pain as the "fifth vital sign" by the Joint Commission of Healthcare Organizations.

REVIEW SUMMARY

At present, therapeutic options are largely limited to drugs approved for other conditions, including anticonvulsants, antidepressants, antiarrhythmics, and opioids. However, treatment based on the underlying disease state (eg, postherpetic neuralgia, diabetic neuropathy) may be less than optimal, in that 2 patients with the same neuropathic pain syndrome may have different symptomatology and thus respond differently to the same treatment. Increases in our understanding of the function of the neurologic system over the last few years have led to new insights into the mechanisms underlying pain symptoms, especially chronic and neuropathic pain.

CONCLUSIONS

The rapidly evolving symptom- and mechanism-based approach to the treatment of neuropathic pain holds promise for improving the quality of life of our patients with neuropathic pain.

A retrospective study of the association between haematological and biochemical parameters and morphine intolerance in patients with cancer pain

BACKGROUND

Morphine is the strong opioid of choice for the treatment of moderate to severe cancer pain according to guidelines of the World Health Organization (WHO). However, a minority of patients do not receive the desired analgesic effect or suffer intolerable side effects from morphine, and are switched to alternative opioids.

METHODS

The aim of this retrospective study was to identify factors that might be associated with morphine intolerance. Data were analysed from 100 controls who tolerated morphine and 77 patients who were switched to an alternative opioid. We investigated whether currently logged data could fully explain the need to switch. Demographic details, cancer type (histological diagnosis) and markers related to organ function were included in an analysis of biochemical and haematological parameters.

RESULTS

Patients over 78 years (P = 0.03), or with a high white cell (P = 0.002) or high platelet count (P = 0.003), were more likely to switch. Although our numbers were small, patients with severe organ impairment were more likely to switch. However, a model including white cell count, platelet count, age, serum albumin and alkaline phosphatase, accurately separated switchers and controls in only 68% of cases. There was no significant difference between the two groups in terms of the numbers of patients having cytotoxic drugs in the two weeks prior to the haematological and biochemical analysis. Similarly, there were no significant differences in histological diagnoses between groups.

CONCLUSIONS

The white cell count was the strongest single effect observed and, as such, warrants further investigation. Further studies are needed in order to accurately define a model that will predict those patients likely to be intolerant of morphine.

Opioids in non-cancer pain: a life-time sentence?

There is continuing reluctance to prescribe strong opioids for the management of chronic non-cancer pain due to concerns about side-effects, physical tolerance, withdrawal and addiction. Randomized controlled trials have now provided evidence for the efficacy of opioids against both nociceptive and neuropathic pain. However, there is considerable variability in response rates, possibly depending on the type of pain, the type of opioid and its route of administration, the time to follow-up, compliance and the development of tolerance. Five patients were selected with nociceptive or neuropathic pain in whom other pharmacological or physical therapies had failed to provide satisfactory pain relief. They received transdermal fentanyl (starting dose 25 microg/h) for at least 6 weeks. Transdermal fentanyl dosage was titrated upwards as required. Transdermal fentanyl provided adequate pain relief in patients with nociceptive pain (diabetic ulcer, osteoporotic vertebral fracture, ankylosing spondylitis) or neuropathic pain with a nociceptive component (radicular pain due to disc protrusion, herpetic neuralgia). The duration of treatment ranged from 6 weeks to 6 months for four cases. In the case of ankylosing spondylitis, treatment was carried out for 2 years, stopped and then restarted successfully. There were no withdrawal effects or addictive behaviour on treatment cessation, regardless of duration of the treatment. In conclusion, strong opioids may provide prolonged effective pain relief in selected patients with nociceptive and neuropathic non-cancer pain. Transdermal fentanyl treatment can often be temporary and can easily be stopped following adequate pain relief without withdrawal effects or any evidence of addictive behaviour.

Strategies for the treatment of cancer pain in the new millennium

As was the case in the era before us, in the new millennium we will continue to see an abundance of patients experiencing cancer-related pain for different reasons. Although much needless pain and suffering still affects many of those with cancer, we are presented with a medical dichotomy. With the analgesic drugs available today, and the relatively simple and effective guidelines to treat cancer pain published and disseminated by the World Health Organization, why do people with cancer continue to experience pain? As we search for the answer, the horizon may hold promising new drugs, 'old drugs' with new interest and applications, and new strategies for the field of pain therapy. Possibilities include the isolation and development of analgesics or analgesic combinations that may minimise the adverse effects which are often associated with the current therapeutic class of opioid analgesics. In addition, current research points to promising results identifying the N-methyl D-aspartate non-opioid receptor as a likely component of neuropathic pain. Drugs such as gabapentin, the mechanism of action of which is not well known, have found favour within the clinical community for their analgesic properties and good tolerability. Methadone, in a phase of resurgence, has garnered the attention of the clinical community because of its unique receptor activity and pharmacoeconomic benefits. A number of clinical studies have demonstrated that methadone has a valuable role in treating cancer pain. Perhaps, an unbalanced focus on the risks of inappropriate use, rather than the benefits, should not compromise or distract from the use of methadone as an alternative to morphine. Studies are on going to assess the potential role of methadone in treating neuropathic pain. Drugs such as cannabinoids, although currently applicable for patients with anorexia, nausea and/or vomiting, may offer benefits to patients experiencing pain. Other opportunities exist with such compounds as alpha2-adrenergic agonists, nicotine, lidocaine and ketamine. New strategies such as the switching opioids and/or their route of administration may offer improved analgesia with fewer adverse effects, thus providing therapeutic alternatives for the clinical community. In addition, there is interest in the co-administration of opioids that act on different receptors. For instance, oxycodone appears to be a kappa opioid receptor agonist and may offer enhanced analgesia when combined with morphine.

Strategies to manage the adverse effects of oral morphine: an evidence-based report

Successful pain management with opioids requires that adequate analgesia be achieved without excessive adverse effects. By these criteria, a substantial minority of patients treated with oral morphine (10% to 30%) do not have a successful outcome because of (1) excessive adverse effects, (2) inadequate analgesia, or (3) a combination of both excessive adverse effects along with inadequate analgesia. The management of excessive adverse effects remains a major clinical challenge. Multiple approaches have been described to address this problem. The clinical challenge of selecting the best option is enhanced by the lack of definitive, evidence-based comparative data. Indeed, this aspect of opioid therapeutics has become a focus of substantial controversy. This study presents evidence-based recommendations for clinical-practice formulated by an Expert Working Group of the European Association of Palliative Care (EAPC) Research NETWORK: These recommendations highlight the need for careful evaluation to distinguish between morphine adverse effects from comorbidity, dehydration, or drug interactions, and initial consideration of dose reduction (possibly by the addition of a co analgesic). If side effects persist, the clinician should consider options of symptomatic management of the adverse effect, opioid rotation, or switching route of systemic administration. The approaches are described and guidelines are provided to aid in selecting between therapeutic options.

Pharmacologic treatment of neuropathic pain

Neuropathic pain, or pain after nervous system injury, can be very refractory to pharmacologic interventions. Through a better understanding of the pathophysiology of neuropathic pain, it has been suggested that nonopioid agents, such as antidepressants and anticonvulsants, may be more efficacious in the treatment of neuropathic pain than common analgesics, such as opioids or nonsteroidal anti-inflammatory drugs. However, this has not been consistently demonstrated in clinical studies. Conversely, many confounding factors of neuropathic pain make it difficult to interpret clinical studies. Therefore, we must develop a better understanding of the preclinical models of neuropathic pain to better understand the application of new and old drugs to the human neuropathic pain state. This article provides an overview of the commonly used preclinical neuropathic pain models, followed by a summary of the efficacy of currently available agents in preclinical pain models and human correlates.

Opioid poorly-responsive cancer pain. Part 1: clinical considerations

Pain that is poorly responsive to opioid analgesics is challenging for physicians who deal with cancer patients. Numerous factors may influence analgesic response during the course of the illness. These include changing nociception associated with disease progression, the appearance of intractable side effects, the development of tolerance, the presence of neuropathic pain, the temporal pattern, the effects produced by the production of opioid metabolites, and many others. These factors influence the delicate balance between pain relief and opioid toxicity that must be achieved in cancer patients with pain.

Opioid and Nonopioid Therapy in Cancer Pain: The Traditional and the New

Management of cancer pain has made sidnificant progress in recent years, partly due to the Agency for Health Care Policy and Research (AHCPR) guidelines, but mostly it seems to be due to the death and dying movement in the world. However, cancer pain on occasion poses significant problems and needs accurate diganosis and appropriate intervention. Pharmacotherapy remains the mainstay of treating cancer pain. Most cancer pain syndromes present with moderate to severe pain, associated with several comorbid problems necessitating the multidisciplinary approach to optimally treat it. The psychologic factors associated wth serious illness, terminal prognoses, and dying complicate the scenario even more as compared with that of nonmalignant pain. Although such patients are entitled to more aggressive analgesic therapy, it is unfortunate that this is not achieved in a significant percentage of cases. In this review, we address some of the above issues and attempt to summarize the traditional pharmacologic therapies highlighting their modern modes of implementation in cancer pain management. Special emphasis on the state-of-the art innovations in this field wil be noted.

The effect of intrathecal endomorphin-2 on the flexor reflex in normal, inflamed and axotomized rats: reduced effect in rats with autotomy

Endomorphin-2, a newly discovered endogenous opioid peptide and agonist at the mu-opioid receptor, was injected intrathecally in normal rats and animals with unilateral peripheral inflammation or sciatic nerve section and its effect on the nociceptive flexor reflex was analysed. In normal rats, intrathecal endomorphin-2 induced a strong and dose-dependent depression of the reflex, which was naloxone-reversible. The effect of intrathecal endomorphin-2 was fairly brief, lasting for about 20-30 min at the highest dose, 4 microg. The effect of endomorphin-2 in inflamed rats was not significantly different from that in normals. After nerve section some rats developed autotomy behavior. In these rats endomorphin-2 had significantly reduced effect. However, the reflex depressive effect of intrathecal endomorphin-2 was unchanged in axotomized rats without autotomy. It is suggested that intrathecal endomorphin-2 has antinociceptive effect in the rat spinal cord under normal and inflammatory conditions. After peripheral nerve injury the sensitivity to endmorphin-2 may be reduced in rats that exhibit ongoing neuropathic pain-like behaviors.

Opioid rotation for cancer pain: rationale and clinical aspects

BACKGROUND

Some patients with cancer pain may develop uncontrolled adverse effects, including generalized myoclonus, delirium, nausea and emesis, or severe sedation before achieving adequate analgesia during opioid dose titration. Sequential therapeutic trials should be considered to determine the most favorable drug.

METHODS

Recent literature was taken into account when reviewing the rationale and potential of opioid rotation.

RESULTS

When aggressive attempts to prevent adverse effects fail, drug rotation should be considered, because sequential therapeutic trials can be useful in identifying the most favorable drug. Different mechanisms, including receptor activity, the asymmetry in cross-tolerance among different opioids, different opioid efficacies, and accumulation of toxic metabolites can explain the differences in analgesic or adverse effect responses among opioids in a clinical setting.

CONCLUSIONS

When pain is relieved inadequately by opioid analgesics given in a dose that causes intolerable side effects despite routine measures to control them, treatment with the same opioid by an alternative route or with an alternative opioid administered by the same route should be considered. Opioid rotation may be useful in opening the therapeutic window and for establishing a more advantageous analgesia/toxicity relationship. By substituting opioids and using lower doses than expected according to the equivalency conversion tables, it is possible in the majority of cases to reduce or relieve the symptoms of opioid toxicity in those patients who were highly tolerant to previous opioids while improving analgesia and, as a consequence, the opioid responsiveness.

Transmitters involved in antinociception in the spinal cord

The possible physiological and pathophysiological role of monoamines-adrenergic transmitter (norepinephrine), serotonin; cholinergic transmitter (acetylcholine); inhibitory (gamma-aminobutyric acid) and excitatory (glutamate) amino acids; opioid and nonopioid peptides, enkephalins, beta-endorphin and substance P, neurokinin-A, neurokinin-B, neurotensin, cytokines, calcitonine gene-related peptide, galanin, neuropeptide Y, nerve growth factor, cholecystokinin; purines; nitric oxide; vanilloid receptor agonists (capasaicin); and nociceptin-in spinal transmission of pain is reviewed. The role of substance P, neurokinin-A and neurokinin-B in the dorsal horn has been identified. These were suggested to be primary afferent transmitters mediating or facilitating the expression of nociceptive inputs. Pronociceptive modulators will be discussed later. Recent findings showing that N-methyl-D-aspartate (NMDA) receptor activation generates nitric oxide and prostanoids that enhance pain transmission whereas adenosine release acts to control these NMDA-mediated events are also mentioned. The clinical importance of centrally acting alpha2-adrenoceptor agonists (clonidine and dexmedetomidine) is also discussed. Antinociceptive and morphine-potentiating drugs are ideal adjuvants for anesthesia; their application in spinal anesthesia is highlighted. The recent development in understanding the importance of noradrenergic transmission and subtypes of alpha2-adrenoceptors (alpha2A and alpha2B) for the first time is reviewed.