Assessment of analgesia in human chronic pain. Randomized double-blind crossover study of once daily repro-dose morphine versus MST continus

Opioids for neuropathic pain

BACKGROUND

This is an updated version of the original Cochrane review published in Issue 3, 2006, which included 23 trials. The use of opioids for neuropathic pain remains controversial. Studies have been small, have yielded equivocal results, and have not established the long-term profile of benefits and risks for people with neuropathic pain.

OBJECTIVES

To reassess the efficacy and safety of opioid agonists for the treatment of neuropathic pain.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (to 24th October 2012), MEDLINE (1966 to 24th October 2012 ), and EMBASE (1980 to 24th October 2012) for articles in any language, and reference lists of reviews and retrieved articles.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) in which opioid agonists were given to treat central or peripheral neuropathic pain of any etiology. Pain was assessed using validated instruments, and adverse events were reported. We excluded studies in which drugs other than opioid agonists were combined with opioids or opioids were administered epidurally or intrathecally.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and included demographic variables, diagnoses, interventions, efficacy, and adverse effects.

MAIN RESULTS

Thirty-one trials met our inclusion criteria, studying 10 different opioids: 23 studies from the original 2006 review and eight additional studies from this updated review.Seventeen studies (392 participants with neuropathic pain, average 22 participants per study) provided efficacy data for acute exposure to opioids over less than 24 hours. Sixteen reported pain outcomes, with contradictory results; 8/16 reported less pain with opioids than placebo, 2/16 reported that some but not all participants benefited, 5/16 reported no difference, and 1/16 reported equivocal results. Six studies with about 170 participants indicated that mean pain scores with opioid were about 15/100 points less than placebo.Fourteen studies (845 participants, average 60 participants per study) were of intermediate duration lasting 12 weeks or less; most studies lasted less than six weeks. Most studies used imputation methods for participant withdrawal known to be associated with considerable bias; none used a method known not to be associated with bias. The evidence, therefore, derives from studies predominantly with features likely to overestimate treatment effects, i.e. small size, short duration, and potentially inadequate handling of dropouts. All demonstrated opioid efficacy for spontaneous neuropathic pain. Meta-analysis demonstrated at least 33% pain relief in 57% of participants receiving an opioid versus 34% of those receiving placebo. The overall point estimate of risk difference was 0.25 (95% confidence interval (CI) 0.13 to 0.37, P < 0.0001), translating to a number needed to treat for an additional beneficial outcome (NNTB) of 4.0 (95% CI 2.7 to 7.7). When the number of participants achieving at least 50% pain relief was analyzed, the overall point estimate of risk difference between opioids (47%) and placebo (30%) was 0.17 (95% CI 0.02 to 0.33, P = 0.03), translating to an NNTB of 5.9 (3.0 to 50.0). In the updated review, opioids did not demonstrate improvement in many aspects of emotional or physical functioning, as measured by various validated questionnaires. Constipation was the most common adverse event (34% opioid versus 9% placebo: number needed to treat for an additional harmful outcome (NNTH) 4.0; 95% CI 3.0 to 5.6), followed by drowsiness (29% opioid versus 14% placebo: NNTH 7.1; 95% CI 4.0 to 33.3), nausea (27% opioid versus 9% placebo: NNTH 6.3; 95% CI 4.0 to 12.5), dizziness (22% opioid versus 8% placebo: NNTH 7.1; 95% CI 5.6 to 10.0), and vomiting (12% opioid versus 4% placebo: NNTH 12.5; 95% CI 6.7 to 100.0). More participants withdrew from opioid treatment due to adverse events (13%) than from placebo (4%) (NNTH 12.5; 95% CI 8.3 to 25.0). Conversely, more participants receiving placebo withdrew due to lack of efficacy (12%) versus (2%) receiving opioids (NNTH -11.1; 95% CI -20.0 to -8.3).

AUTHORS' CONCLUSIONS

Since the last version of this review, new studies were found providing additional information. Data were reanalyzed but the results did not alter any of our previously published conclusions. Short-term studies provide only equivocal evidence regarding the efficacy of opioids in reducing the intensity of neuropathic pain. Intermediate-term studies demonstrated significant efficacy of opioids over placebo, but these results are likely to be subject to significant bias because of small size, short duration, and potentially inadequate handling of dropouts. Analgesic efficacy of opioids in chronic neuropathic pain is subject to considerable uncertainty.  Reported adverse events of opioids were common but not life-threatening. Further randomized controlled trials are needed to establish unbiased estimates of long-term efficacy, safety (including addiction potential), and effects on quality of life.

Long-term opioid treatment of chronic nonmalignant pain: unproven efficacy and neglected safety?

BACKGROUND

For the past 30 years, opioids have been used to treat chronic nonmalignant pain. This study tests the following hypotheses: (1) there is no strong evidence-based foundation for the conclusion that long-term opioid treatment of chronic nonmalignant pain is effective; and (2) the main problem associated with the safety of such treatment - assessment of the risk of addiction - has been neglected.

METHODS

Scientometric analysis of the articles representing clinical research in this area was performed to assess (1) the quality of presented evidence (type of study); and (2) the duration of the treatment phase. The sufficiency of representation of addiction was assessed by counting the number of articles that represent (1) editorials; (2) articles in the top specialty journals; and (3) articles with titles clearly indicating that the addiction-related safety is involved (topic-in-title articles).

RESULTS

Not a single randomized controlled trial with opioid treatment lasting >3 months was found. All studies with a duration of opioid treatment ≥6 months (n = 16) were conducted without a proper control group. Such studies cannot provide the consistent good-quality evidence necessary for a strong clinical recommendation. There were profound differences in the number of addiction articles related specifically to chronic nonmalignant pain patients and to opioid addiction in general. An inadequate number of chronic pain-related publications were observed with all three types of counted articles: editorials, articles in the top specialty journals, and topic-in-title articles.

CONCLUSION

There is no strong evidence-based foundation for the conclusion that long-term opioid treatment of chronic nonmalignant pain is effective. The above identified signs indicating neglect of addiction associated with the opioid treatment of chronic nonmalignant pain were present.

Review Article: Chronobiology: influence of circadian rhythms on the therapy of severe pain

Modern pain therapy widely follows the WHO (World Health Organization) guidelines using a three-step ‘ladder’ for pain relief. This escalating step scheme includes the administration in the order nonopioids, mild opioids and strong opioids, and adjuvants at any step. Analgesics should be given ‘by the clock’ rather than ‘on demand’. However, the chronobiological parameters circadian pain rhythm, circadian efficacy of analgesics, and individual circadian need for analgesics are to be considered. The results of a multitude of studies in chronobiology are not consistent. Therefore, further studies with standardized protocols are needed that allow to assign more consistent rhythms to diseases, pain causes, and analgesic efficacy of opioids. In many cases, each patient perceives pain and its intensity individually during the time of day. By administration of analgesics over a constant or continuous dosage time fluctuations in pain perception and the outcomes of many studies in chronobiology are ignored that prove the influence of biological rhythms on the pharmacokinetic and pharmacodynamic aspects of analgesics. As different types of pain show different rhythms (highest pain intensities arising at different times of the day) analgesics should be dosed flexibly. It is also very important that drug therapy can be adjusted individually to the pain rhythm of the patient as well as to the type and cause of pain. In severe pain, therapy should be particularly careful. A flexible dosage depending on pain intensity and rapid dose adjustment are essentials of a modern pain therapy. Therefore, opioids that are flexible to use are better suited to treat the individual pain of the patient than rigid modified release oral or transdermal systems. J Oncol Pharm Practice (2010) 16: 81—87.

[Differential therapeutic aspects of analgesia with oral sustained-release strong opioids: application intervals, metabolism and immunosuppression]

The oral "around-the clock" administration of sustained-release strong opioids has been recommended for the long-term treatment of patients suffering from chronic severe pain. At present a plethora of products are available in Germany. Modern galenics even allow for only once-daily oral application without clinically relevant negative chronobiological interference. This application scheme has been shown to improve compliance and sleep quality, factors that influence treatment outcome. Randomized controlled studies revealed no relevant differences between the different strong opioids with respect to efficacy and tolerability. However, hydromorphone and oxycodone appear to be advantageous over morphine due to a lack of immunosuppression. Hydromorphone has the additional benefit of a lower risk of intoxication by accumulation of active metabolites in patients with decreased renal function. As a result, although morphine has been regarded as the standard for the treatment of chronic severe pain, hydromorphone and oxycodone may be better and safer alternatives for certain patient groups (e.g. older age, multimorbidity, cancer).

Epidemiology of regular prescribed opioid use: results from a national, population-based survey

Chronic pain occurs commonly and accounts for significant suffering and costs. Although use of opioids for treatment of chronic pain is increasing, little is known about patients who use opioids regularly. We report data from the second wave of the Healthcare for Communities survey (2000-2001), a large, nationally representative household survey. We compared regular users of prescription opioids to nonusers of opioids and calculated the percentage of individuals within a given demographic or disease state that reported chronic opioid use. Approximately 2% of the 7,909 survey respondents reported use of opioid medications for at least a month, which the Healthcare for Communities survey defined as "regular use." Opioid users were more likely than nonusers to report high levels of pain interference with their daily lives and to rate their health as fair or poor. Arthritis and back pain were the most prevalent chronic, physical health conditions among users of opioids, with 63% of regular users of opioids reporting arthritis and 59% reporting back pain. The majority of regular users of opioids had multiple pain conditions (mean=1.9 pain conditions). Regular opioid users appear to have an overall lower level of health status and to have multiple, chronic physical health disorders.

Opioids for neuropathic pain

BACKGROUND

The use of opioids for neuropathic pain remains controversial. Studies have been small, have yielded equivocal results, and have not established the long-term risk-benefit ratio of this treatment.

OBJECTIVES

To assess the efficacy and safety of opioid agonists for the treatment of neuropathic pain.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (2nd Quarter 2005), MEDLINE (1966 to June 2005), and EMBASE (1980 to 2005 Week 27) for articles in any language, and reference lists of reviews and retrieved articles.

SELECTION CRITERIA

Trials were included in which opioid agonists were given to treat central or peripheral neuropathic pain of any etiology, pain was assessed using validated instruments, and adverse events were reported. Studies in which drugs other than opioid agonists were combined with opioids or opioids were administered epidurally or intrathecally were excluded.

DATA COLLECTION AND ANALYSIS

Data were extracted by two independent investigators and included demographic variables, diagnoses, interventions, efficacy, and adverse effects.

MAIN RESULTS

Twenty-three trials met the inclusion criteria and were classified as short-term (less than 24 hours; n = 14) or intermediate-term (median = 28 days; range = eight to 70 days; n = 9). The short-term trials had contradictory results. In contrast all nine intermediate-term trials demonstrated opioid efficacy for spontaneous neuropathic pain. Meta-analysis of seven intermediate-term studies showed mean post-treatment visual analog scale scores of pain intensity after opioids to be 13 points lower on a scale from zero to 100 than after placebo (95% confidence interval -16 to -9; P < 0.00001). The most common adverse events were nausea (33% opioid versus 9% control: number needed to treat to harm (NNH) 4.2) and constipation (33% opioid versus 10% control: NNH 4.2), followed by drowsiness (29% opioid versus 12% control: NNH 6.2), dizziness (21% opioid versus 6% control: NNH 7.1), and vomiting (15% opioid versus 3% control: NNH 8.3). Where reported, 23 (11%) of 212 participants withdrew because of adverse events during opioid therapy versus nine (4%) of 202 receiving placebo.

AUTHORS' CONCLUSIONS

Short-term studies provide only equivocal evidence regarding the efficacy of opioids in reducing the intensity of neuropathic pain, whereas intermediate-term studies demonstrate significant efficacy of opioids over placebo, which is likely to be clinically important. Reported adverse events of opioids are common but not life threatening. Further randomized controlled trials are needed to establish long-term efficacy, safety (including addiction potential), and effects on quality of life.

Recommendations for using opioids in chronic non-cancer pain

1. The management of chronic pain should be directed by the underlying cause of the pain. Whatever the cause, the primary goal of patient care should be symptom control. 2. Opioid treatment should be considered for both continuous neuropathic and nociceptive pain if other reasonable therapies fail to provide adequate analgesia within a reasonable timeframe. 3. The aim of opioid treatment is to relieve pain and improve the patient's quality of life. Both of these should be assessed during a trial period. 4. The prescribing physician should be familiar with the patient's psychosocial status. 5. The use of sustained-release opioids administered at regular intervals is recommended. 6. Treatment should be monitored. 7. A contract setting out the patient's rights and responsibilities may help to emphasize the importance of patient involvement. 8. Opioid treatment should not be considered a lifelong treatment.

Assessment of biodegradable controlled release rod systems for pain relief applications

Control of chronic, severe pain is a difficult and important clinical problem for most patients, especially those with cancer. Although current applications are insufficient for a satisfactory solution to this problem, the rate of disease incidence is increasing worldwide, thus making the problem more apparent. Based on this fact, this study was designed with the ultimate goal of formulating a controlled release system of pain relievers, mainly opioids, for the local treatment of pain to achieve satisfactory, fast, and less side effect-related relief and to provide a better life status for chronic pain patients. Two copolymers of a biodegradable polymer poly(L-lactide-co-glycolide) (PLGA) were used to prepare an implantable rod type drug release system containing either an analgesic or anesthetic type of pain reliever. In vitro drug release kinetics of these systems were studied. It was observed that release from PLGA 85 : 15 was more zero-order than it was from PLGA 50 : 50. A zero-order release rate was obtained for codeine, hydromorphone, and bupivacaine from PLGA (85 : 15) rods. They, however, were released from PLGA (50 : 50) rods with Higuchi kinetics. The drug solubility was also influential on release rate, as shown by the zero-order morphine release from PLGA (50 : 50) rods. Scanning electron micrographs (SEMs) of the monolithic rods revealed erosion of the rods and the removal of drug crystals from the rod structure.

Oncology outpatients with pain from bone metastasis require more than around-the-clock dosing of analgesics to achieve adequate pain control

Around-the-clock (ATC) dosing of opioid analgesics is the established approach for the management of chronic cancer pain. The purposes of this study were to determine whether there were differences in pain intensity scores and pain duration between oncology outpatients who were taking opioid analgesics on an around-the-clock (ATC) compared with an as needed (PRN) basis and to determine differences in opioid prescription and consumption between the 2 groups during a period of 5 weeks. Oncology patients (n = 137) with pain from bone metastasis were recruited from 7 outpatient settings. Patients completed a demographic questionnaire and on a daily basis recorded pain intensity scores and medication intake in a diary. No significant differences in average, least, or worst pain intensity scores or number of hours per day in pain were found between the 2 groups. However, the average total opioid dose, prescribed and taken, was significantly greater for the ATC group than for the PRN group. These findings suggest the need for further investigations in the following areas: the appropriate treatments for pain related to bone metastasis, the use of various pain measures to evaluate the effectiveness of analgesic medications, and the need to evaluate how analgesics are prescribed and titrated for patients with cancer-related pain.

Opiate self-administration as a measure of chronic nociceptive pain in arthritic rats

The study examined the validity of oral fentanyl self-administration (FSA) as a measure of the chronic nociceptive pain that develops in rats with adjuvant arthritis independently of acute noxious challenges. Arthritic rats self-administered more of a 0.008 mg/ml fentanyl solution (up to 3.4 g/rat per day) than non-arthritic controls (0.5 g/rat per day) and did so with a biphasic time course that reached peak during weeks 3 and 4 after inoculation with Mycobacterium butyricum. The time course paralleled both the disease process and the chronic pain. Continuous infusion of dexamethasone during weeks 3 and 4 via subcutaneous osmotic pumps at 0.0025-0.04 mg/rat per day disrupted the arthritic disease and decreased FSA to a level (i.e. by 65%) similar to that observed in non-arthritic rats. Continuous naloxone (2.5 mg/rat per day) decreased FSA (by 55%) in arthritic but not in non-arthritic animals. Continuous, subcutaneous infusion of fentanyl also decreased arthritic FSA in a manner that varied with dose at 0.04-0.16 mg/rat per day doses, but leveled off at 47% of controls with 0.31 mg/rat per day. The effects of continuous fentanyl on arthritic FSA occurred only with those doses and dose-dependent dynamics with which fentanyl also induced dependence in non-arthritic rats. The findings indicate that pain, rather than the rewarding or dependence-inducing action of fentanyl mediates FSA in arthritic rats. Paralleling patient-controlled analgesic drug intake, FSA offers a specific measure allowing the dynamic effects of neurobiological agents to be studied in this unique animal model of persistent nociceptive pain.