Opioid tolerance and dependence - do they matter?

Nociceptive pain assessed by the PainDETECT questionnaire may predict response to opioid treatment for chronic low back pain

Introduction

The pharmacological management of chronic low back pain (LBP) is complex. The World Health Organisation recommends a laddered approach to pain medication usage. The PainDETECT questionnaire distinguishes between neuropathic pain (NeP), nociceptive pain (NoP), and ambiguous pain. By elucidating the difference in medication efficacy between these groups, clinicians can provide a tailored treatment plan to manage patient's pain. This study aimed to investigate the relationship between pharmacological treatments, pain categorizations, and medication efficacy as reported by patients.

Methods

A secondary retrospective analysis of a prospectively collected database was conducted involving 318 consecutively recruited patients, aged 18 years and above, who completed PainDETECT, medication history and patient reported medication efficacy questionnaires. Medication history was categorized into four lines of treatment: first line (paracetamol ± non-prescribed anti-inflammatories), second line (prescribed anti-inflammatories), third line (anticonvulsants/neuromodulators) and fourth line (opioids). Medication efficacy was measured using a three-point Likert scale: effective (+2), somewhat effective (+1), no effect (0).

Findings

The study included 120, 50, 54 and 94 patients on first line, second line, third line and fourth line treatment, respectively. The NeP group had higher mean numerical rating scale (NRS) compared to NoP group in all four lines of treatment (8.10 ± 1.59 vs. 5.47± 2.27, p < 0.001, 8.64± 1.43 vs. 5.52± 1.86, p < 0.001, 8.00± 1.07 vs. 6.37± 2.39, p < 0.01, and 8.05± 1.73 vs. 7.2± 1.29, p < 0.05). When confounding for severity of LBP as measured by NRS, the distribution of medication efficacy significantly differed amongst the NeP, ambiguous and NoP groups in patients undergoing fourth line pharmacological treatment (r2 = 8.623, p < 0.05). The NoP group exhibited significantly higher medication efficacy compared to the NeP group (U = 14.038, p < 0.05). There was no significant difference in medication efficacy across the pain classifications for first, second- and third-line treatment.

Interpretation

Opioids was the only line of treatment more effective in targeting NoP, as determined by the PainDETECT questionnaire, compared to NeP. This pioneering study illustrates the complex nature of pharmacological management for chronic LBP. It underscores the importance of tailoring pharmacological treatment plans to fit individual pain profiles and expectations instead of adopting a blanket approach to pain management.

Opioid epidemic: lessons learned and updated recommendations for misuse involving prescription versus non-prescription opioids

INTRODUCTION

In the past decades, the opioid crisis has heavily impacted parts of the US society and has been followed by an increase in the use of opioids worldwide. It is of paramount importance that we explore the origins of the US opioid epidemic to develop best practices to tackle the rising tide of opioid overdoses.

AREAS COVERED

In this expert review, we discuss opioid (over)prescription, change in perception of pain, and false advertisement of opioid safety as the leading causes of the US opioid epidemic. Then, we review the evidence about opioid dependence and addiction potential and provide current knowledge about predictors of aberrant opioid-related behavior. Lastly, we discuss different approaches that were considered or undertaken to combat the rising tide of opioid-related deaths by regulatory bodies, pharmaceutical companies, and health-care professionals. For this expert review, we considered published articles relevant to the topic under investigation that we retrieved from Medline or Google scholar electronic database.

EXPERT OPINION

The opioid epidemic is a dynamic process with many underlying mechanisms. Therefore, no single approach may be best suited to combat it. In our opinion, the best way forward is to employ multiple strategies to tackle different underlying mechanisms.

Effect of Nectaroscordum koelzi Methanolic Extract on Acute and Chronic Inflammation in Male Mice

INTRODUCTION

The present study deals with the effect of Nectaroscordum koelzi fruit extract on acute and chronic inflammation.

METHODS

A total of 84 NMRI mice were used in this study. The effect of the extract on acute inflammation was analyzed by increasing vascular permeability via acetic acid and xylene induced ear edema among mice. The extract was evaluated in terms of effects on chronic inflammation by means of the cotton pellet test among mice. For the assessment of inflammation degree, the mice paw edema volume was measured by the plethysmometric test.

RESULTS

The findings showed that the extract was effective on acute inflammation induced by acetic acid in mice. In the xylene ear edema, N. koelzi extract indicated a significant activity in mice. In the cotton pellet method, the methanol extract produced a significant reduction in comparison with the control and dexamethasone. Mice paw edema volume decreased with the extract.

CONCLUSION

In general, the data from the experiments indicated that the methanol extract of N. koelzi has an anti-inflammatory effect on acute and chronic inflammation. However, the exact contributing mechanisms have not been investigated for the pharmacological effects.

Limited potential of cebranopadol to produce opioid-type physical dependence in rodents

Cebranopadol is a novel potent analgesic agonist at the nociceptin/orphanin FQ peptide (NOP) and classical opioid receptors. As NOP receptor activation has been shown to reduce side effects related to the activation of μ-opioid peptide (MOP) receptors, the present study evaluated opioid-type physical dependence produced by cebranopadol in mice and rats. In a naloxone-precipitated withdrawal assay in mice, a regimen of seven escalating doses of cebranopadol over 2 days produced only very limited physical dependence as evidenced by very little withdrawal symptoms (jumping) even at cebranopadol doses clearly exceeding the analgesic dose range. In contrast, mice showed clear withdrawal symptoms when treated with morphine within the analgesic dose range. In the rat, spontaneous withdrawal (by cessation of drug treatment; in terms of weight loss and behavioral score) was studied after 4-week subacute administration. Naloxone-precipitated withdrawal (in terms of weight loss and behavioral score) was studied in the same groups of rats after 1-week re-administration following the spontaneous withdrawal period. In both tests, cebranopadol-treated rats showed only few signs of withdrawal, while withdrawal effects in rats treated with morphine were clearly evident. These findings demonstrate a low potential of cebranopadol to produce opioid-type physical dependence in rodents. The prospect of this promising finding into the clinical setting remains to be established.

AMPA receptor positive allosteric modulators attenuate morphine tolerance and dependence

Development of opioid tolerance and dependence hinders the use of opioids for the treatment of chronic pain. In searching for the mechanism and potential intervention for opioid tolerance and dependence, we studied the action of two positive allosteric modulators of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR PAMs). In mice treated with morphine (100 mg/kg, s.c.), acute morphine tolerance and dependence developed in 4-6 h. Treatment with aniracetam, a well-established AMPAR PAM, was able to completely prevent and reverse the development of acute antinociceptive tolerance to morphine. Partial, but significant, effects of aniracetam on acute morphine induced-physical dependence were also observed. Moreover, aniracetam significantly reversed the established morphine tolerance and dependence in a chronic model of morphine tolerance and dependence produced by intermittent morphine (10 mg/kg, s.c. for 5d). In addition, HJC0122, a new AMPAR PAM was found to have similar effects as aniracetam but with a higher potency. These previously undisclosed actions of AMPAR PAMs are intriguing and may shed lights on understanding the APMA signaling pathway in opioid addiction. Moreover, these data suggest that AMPAR PAMs may have utility in preventing and treating morphine tolerance and dependence.

Antinociceptive effects of the aqueous and methanol extracts of the leaves of Pittosporum mannii Hook. F. (Pittosporaceae) in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Pittosporum mannii (Pittosporaceae) is used in Africa traditional medicine to treat various ailments including pain and inflammation.

AIM OF THE STUDY

The present work was undertaken to evaluate the antinociceptive effects of the aqueous (AEPM) and methanol (MEPM) extracts from the leaves of Pittosporum mannii.

METHODS

High performance liquid chromatography coupled with mass spectrometry (LCMS) was used for the phytochemical analysis of AEPM prepared as decoction and MEPM prepared as cold maceration. The in vitro cytotoxicity of AEPM and MEPM were evaluated on Artemia salina larvae. AEPM and MEPM antinociceptive effects were evaluated at the doses of 35, 75, 150 and 300mg/kg given orally, against pain induced by acetic acid, formalin, hot plate, capsaicin and glutamate. The rota rod test was also performed at the same doses. To determine the mechanism of action of these extracts, their antinociceptive effects were tested in animals pretreated with yohimbine (α2-adrenergic antagonist), atropine (muscarinic antagonist) or naloxone (an opioids antagonist).

RESULT

The LCMS analysis showed that both extracts contain pittovidoside and 1-O-rhamnopyranosyl-23-acetoxyimberbic acid 29-methyl ester, the aqueous extract being more concentrated. Oral administration of both extracts significantly reduced pain symptoms induced by acetic acid, formalin, capsaicin, glutamate and hot plate. The antinociceptive effect of AEPM was significantly inhibited by yohimbine, atropine and naloxone while these inhibitors tend to potentiate the activity of MEPM. Both extracts have no effect on Rota rod test. AEPM and MEPM showed respective LC50 of 2.44 and 0.70mg/ml on Artemia larvae and were therefore, considered non-toxic.

CONCLUSION

These results indicate that AEPM and MEPM possesses analgesic effects with different mechanism of action. Although effects of both extracts may involve TRPV1 receptors and glutamatergic pathway, AEPM may in addition, interact with alpha-adrenergic, muscarinic and opioidergic pathways that are not involve in the effects of MEPM.

Attenuation of Withdrawal Signs, Blood Cortisol, and Glucose Level with Various Dosage Regimens of Morphine after Precipitated Withdrawal Syndrome in Mice

Morphine withdrawal usually results in unsuccessful outcomes. Despite partial benefits from alternative substances such as methadone, its use may not lead to the desired result due to the lack of mental tranquility during the withdrawal period. In this study, by means of an animal model, morphine itself was used to manage morphine dependence. Forty mice were divided into 5 groups, in which 4 groups became dependent by increasing daily doses of morphine for 7 days (15-45 mg/kg). Afterwards, the animals received morphine for 14 days by either of the following regimens: Once daily 45 mg/kg (positive controls)Increasing the interval (each time 6 hours longer than the previous interval)Irregular interval in every 36, 12 and 24 hours until the 21(th) day12, 24, 36 hours decreasing doses (each time 2.5 mg/kg less than the former dosage). Negative controls received saline solution only. On day 22, total withdrawal index (TWI) was determined by injecting 3 mg/kg of naloxone. Thereafter, blood samples were taken for the measurement of cortisol and glucose levels. TWI significantly decreased in all test groups in comparison with the positive control animals (P<0.001). Cortisol levels significantly decreased when either the dosage or the administration frequencies were decreased on a regular and gradual basis (P<0.005). Blood glucose levels significantly decreased in animals that received decreasing doses of morphine (P<0.005). This study suggests that no other measures may be required in clinical practice except for changing the dosage regimen of morphine for the cessation of self-administration.

Involvement of the NO/cGMP/KATP pathway in the antinociceptive effect of the new pyrazole 5-(1-(3-fluorophenyl)-1H-pyrazol-4-yl)-2H-tetrazole (LQFM-021)

The pyrazol compounds are known to possess antipyretic, analgesic and anti-inflammatory activities. This study was conducted to investigate the peripheral antinociceptive effect of the pyrazole compound 5-(1-(3-Fluorophenyl)-1H-pyrazol-4-yl)-2H-tetrazole (LQFM-021) and involvement of opioid receptors and of the NO/cGMP/K(ATP) pathway. The oral treatments in mice with LQFM-021 (17, 75 or 300 mg/kg) decreased the number of writhing. In the formalin test, the treatments with LQFM-021 at doses of 15, 30 and 60 mg/kg reduced the licking time at both neurogenic and inflammatory phases of this test. The treatment of the animals with LQFM-021 (30 mg/kg) did not have antinociceptive effects in the tail-flick and hot plate tests. Furthermore, pre-treatment with naloxone (3 mg/kg i.p.), L-name (10 mg/kg i.p.), ODQ (10 mg/kg i.p.) or glibenclamide (3 mg/kg i.p.) antagonized the antinociceptive effect of LQFM-021 in both phases of the formalin test. In addition, it was also demonstrated that the treatments of mice with LQFM-021(15, 30 and 60 mg/kg) did not compromise the motor activity of the animals in the chimney test. Only the highest dose used in the antinociceptive study promoted changes in the open field test and pentobarbital-induced sleep test, thus ruling out possible false positive effects on nociception tests. Our data suggest that the peripheral antinociception effects of the LQFM-021 were mediated through the peripheral opioid receptors with activation of the NO/cGMP/KATP pathway.

[Management of postoperative pain in ear-nose-throat surgery]

The degree of pain following different types of ear-nose-throat surgery varies greatly and must be adjusted on an individual basis. Post-operative pain therapy can be classified into basic pain therapy and additive pain therapy (as needed). Effective pain therapy can lead to lower morbidity and to considerable economic advantages. The subjective pain intensity experienced by patient should be the basis for the dose adaptation and is essential for rapid recovery.

[Chronic non-cancer-related pain. Long-term treatment with rapid-release and short-acting opioids in the context of misuse and dependency]

Annually published data show a continual increase in the volume of opioid prescriptions in Germany, thus indicating an intensification of opioid therapy. The majority of opioids are prescribed to treat chronic non-cancer-related pain. On the basis of current guidelines, as well as in terms of the lack of data regarding long-term use of opioids and their effectiveness beyond a period of 3 months, this development must be viewed critically. With reference to four case reports, we discuss and evaluate opioid therapy in relation to medication misuse and the development of drug dependency. Particular emphasis is placed on the administration of rapid-release and short-acting opioid preparations, which we consider to be particularly problematic.

End-of-dose pain in chronic pain: does it vary with the use of different long-acting opioids?

A large percentage of patients with chronic pain on around-the-clock (ATC) opioids may experience increased pain occurring at the end of a scheduled dose, also known as end-of-dose pain. Despite the significant prevalence and impact of end-of-dose pain in patients using extended-release (ER) opioids, there are no detailed analyses examining how the frequency of end-of-dose pain is linked to the formulations of long-acting opioids. Consequently, we performed a systematic review to evaluate how many published studies on patients with chronic cancer or noncancer pain identified end-of-dose pain. As only a few studies mentioned end-of-dose pain explicitly, we used breakthrough pain (BTP) as a surrogate parameter. We determined if any opioid formulation had a greater association with the frequency of BTP, the use of rescue medication for BTP, and the frequency of end-of-dose pain. Of the 39 studies entered in the final analysis, 14 studies across different formulations showed that ER opioids were effective in the prevention of BTP. The opioids most frequently studied were hydromorphone (26%), followed by morphine (23%), and transdermal buprenorphine (23%). Only 5% of the studies used immediate-release preparations. Overall, most studies showed that patients using ER preparations experienced fewer episodes of BTP compared with patients on placebo or an active comparator. This could reflect the favorable duration of action of these opioids compared with short-acting formulations. Future studies should examine the incidence of end-of-dose pain and use of rescue medicine in a longitudinal manner in patients with chronic pain taking short- vs. long-acting ATC opioids.

Acquired pharmaco-dynamic opioid tolerance: a concept analysis

AIM

To report an analysis of the concept of acquired pharmaco-dynamic opioid tolerance.

BACKGROUND

Acquired pharmaco-dynamic opioid tolerance is a complex and poorly understood phenomenon associated with strong opioid therapy for managing pain. Critical review of the concept provides greater clarification of the attributes, assisting healthcare professionals in addressing pain and functional management of patients, particularly those with non-malignant pain.

DESIGN

Concept analysis.

DATA SOURCES

A systematic literature search was undertaken using electronic data bases: CINAHL, British Nursing Index, EMBase, Medline, Pubmed and AMED. All literature reviewed was in English and published between 1976 and 2012. The key search terms were 'chronic non-malignant pain', 'strong opioid therapy' and 'development of acquired pharmaco-dynamic opioid tolerance'; all possible variant terms were also searched.

METHOD

The Walker and Avant approach was used to guide the concept analysis.

RESULTS

The concept analysis revealed four empirical referents: plasticity, drug administration, reduced analgesic efficacy and increased drug dosing. Tachyphylexia was identified as a borderline case, opioid induced hyperalgesia as a related case and pseudo-tolerance as a contrary case. The antecedent is administration of an opioid analgesic drug and the consequences, increasing opioid drug dose to maintain analgesic effect.

CONCLUSION

Untangling the antecedents, empirical referents and consequences of tolerance help healthcare professionals understand its complexities. Improved knowledge may ultimately influence patient outcomes through the construction of better monitoring systems. This concept analysis may also provide insights for policy change and give empirical direction for future research.

Chemical Characterization and In Vivo Anti-Inflammatory Activities of Actinidia callosa var. ephippioides via Suppression of Proinflammatory Cytokines

Actinidia callosa var. ephippioides (ACE) has been widely used to treat anti-pyretic, antinociceptive, anti-inflammation, abdominal pain and fever in Taiwan. This study aims to determine the mechanism of anti-inflammatory activities of ethyl acetate fraction of ACE (EA-ACE) using a model of λ-carrageenan (Carr)-induced paw edema in mouse model. In HPLC analysis, chemical characterization of EA-ACE was established. In order to investigate the anti-inflammatory mechanism of EA-ACE, we have detected the activities of catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) and the levels of malondialdehyde (MDA) in the paw edema. Serum NO, tumor necrosis factor α (TNF-α), and interleukin-1β (IL-1β) were evaluated. Chemical characterization from HPLC indicated that EA-ACE contains betulinic acid, ursolic acid and oleanolic acid. In the anti-inflammatory test, EA-ACE decreased the paw edema after Carr administration, increased the activities of CAT, SOD, and GPx and decreased the MDA level in the edema paw at the 5th hr after Carr injection. EA-ACE affects the serum NO, TNF-α, and IL-1β levels at the 5th hr after Carr injection. EA-ACE decreased Carr-induced inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expressions by Western blotting. Actinidia callosa var. ephippioides have the potential to provide a therapeutic approach to inflammation-associated disorders.

Acute pain management in the opioid-tolerant patient

SUMMARY Opioid use is increasing worldwide leading to an increasing number of opioid-tolerant patients requiring acute pain management after surgery, trauma and acute diseases. Provision of analgesia in opioid-tolerant patients is complex due to the pharmacological effects of long-term opioid exposure, but also due to pre-existing pain states, comorbidities and psychosocial issues. Acute pain management in these patients is governed by the principles of provision of good analgesia, avoidance of withdrawal and organized discharge. Pain relief needs to be achieved by the use of multimodal analgesia, including regional anesthetic techniques and, if needed, opioids in increased doses. Withdrawal is best prevented by ongoing opioid substitution at previously established doses. Discharge planning requires multidisciplinary input and good communication with all healthcare providers involved.

Convolutamydine A and synthetic analogues have antinociceptive properties in mice

Convolutamydine A, an oxindole that originated from a marine bryozoan, has several biological effects. In this study, we aimed to investigate the antinociceptive effects of convolutamydine A and two new synthetic analogues. Convolutamydine A and the two analogues were given orally to assess their ability to induce antinociceptive effects. Formalin-induced licking response, acetic acid-induced contortions, and hot plate models were used to characterize the effects of convolutamydine A and its analogues. Convolutamydine A (4,6-bromo-3-(2-oxopropyl)-3-hydroxy-2-oxindole), compound 1 (3-(2-oxopropyl)-3-hydroxy-2-oxindole), and compound 2 (5-bromo-3-(2-oxopropyl)-3-hydroxy-2-oxindole) caused peripheral antinociceptive and anti-inflammatory effects in the acetic acid-induced contortions and the formalin-induced licking models. Supraspinal effects were also observed in the hot plate model and were similar to those obtained with morphine. The peripheral effects were not mediated by the cholinergic or opioid systems. The antinociceptive effects of convolutamydine A seem to be mediated by all three systems (cholinergic, opioid, and nitric oxide systems), and the mechanism of action of compounds 1 and 2 involved cholinergic and nitric oxide-mediated mechanisms. Convolutamydine A and its analogues (compounds 1 and 2) showed good antinociceptive ability after systemic administration in acute pain models. The antinociceptive action mediated by cholinergic, opioid, and nitric oxide systems could explain why convolutamydine A, compound 1, and compound 2 retained their antinociceptive effects. The doses used were similar to the doses of morphine and were much lower than that of acetylsalicylic acid, the classical analgesic and anti-inflammatory drug. In conclusion, convolutamydine A and the two analogues demonstrated antinociceptive effects comparable to morphine's effects.

Effects of repeated oxycodone administration on its analgesic and subjective effects in normal, healthy volunteers

Tolerance to the analgesic effects of opioids has been demonstrated in laboratory animals after repeated drug administration; yet, this effect has been studied less frequently under controlled laboratory conditions in humans. This within-subject, double-blind, placebo-controlled study was designed to determine whether tolerance developed to the analgesic, subjective, and physiological effects of the commonly prescribed opioid oxycodone when it was administered daily for 5 days. The effects of oxycodone (0, 5, and 20 mg/70 kg, orally) were compared, using a within-session cumulative dosing procedure, on the first and fifth days of the 'daily' dosing phase to assess for tolerance; active oxycodone was administered on the second and fourth days of the daily dosing phase. Changes in the effects of oxycodone were also compared when the medication was only administered on the first and the fifth day of a 5-day 'intermittent' dosing phase; placebo medication was administered on the second and fourth days of the intermittent dosing phase. A 9-day 'washout' period occurred between phases during which no medication was administered. Healthy volunteers (N=10) with no history of drug dependence or current drug use participated in this outpatient study. Analgesia was assessed using the cold pressor test, pain and drug effects were measured using a variety of questionnaires, and pupil diameter was monitored as an index of physiological effects. When administered daily, no differences were observed in oxycodone-induced analgesia between the first and the fifth days, but tolerance did develop to some of the positive subjective effects of oxycodone. In contrast, oxycodone-induced analgesia and participant ratings of some positive subjective drug effects were greater on the fifth compared with the first day of the intermittent dosing phase. No differences in the miotic effects of oxycodone between the first and the fifth days of either dosing phase were detected. Although obtained under limited experimental conditions, these findings suggest that tolerance may not develop to the analgesic effects of therapeutic doses of oxycodone under short-term daily dosing conditions, even though some of its subjective effects may decrease. These data also suggest that intermittent administration may enhance the analgesic effects of oxycodone, while also increasing some of the drug's positive subjective effects related to abuse liability.

Opioid-induced hyperalgesia (OIH)

BACKGROUND AND OBJECTIVES

Opioids are commonly used for pain control; however, they can cause hyperalgesia. The reason why this can happen is not known. The objective of this review was to describe the mechanisms, factors implicated, and drug modulation.

CONTENTS

The factors implicated in the development of opioid-induced hyperalgesia (OIH), such as duration of use, dose, and type of opioids are described. Mechanisms involved include the glutamatergic system and N-methyl-D-aspartate receptors (NMDA), spinal cyclooxygenase (COX) activation, excitatory amino acids, dynorphin, cytokines and chemokines; prostaglandins, and descending facilitation. Modulation of hyperalgesia could be done through: NMDA receptor antagonists, alpha2-adrenergic agonists, and COX inhibitors.

CONCLUSIONS

This is a very complex subject, which involves a series of pathophysiological mechanisms that could contribute for OIH and patient discomfort, bringing disastrous consequences.

[Opioids for chronic noncancer pain: recommendations based on clinical practice guidelines]

OBJECTIVE

The need for major opioids in the treatment of chronic pain unrelated to cancer is increasing. We therefore appraised available clinical practice guidelines in order to identify recommendations for good practice in the use of these drugs.

MATERIAL AND METHODS

By searching the main guideline repositories as well as resources provided by medical associations, we identified clinical practice guidelines on the use of major opioids published up to 2007. Fourteen of the 28 guidelines we found met the inclusion criteria. To appraise the guidelines we applied the criteria for scientific evidence of the AGREE collaboration (Appraisal of Guidelines Research and Evaluation). The AGREE instrument consists of 23 items organized in 6 areas for appraisal.

RESULTS

Of the 14 guidelines appraised, 5 were judged to be of high quality. In each of the 5 selected guidelines, the relation between a recommendation and the evidence it was based on was stated explicitly; all 5 had overall quality scores over 60%. The recommendations drawn from these guidelines deal with 3 sequential moments in the use of opioids: start of treatment, maintenance therapy, and withdrawal of the drug.

CONCLUSION

The use of opioids to treat chronic noncancer pain is controversial in terms of effectiveness, safety, and the possibility of addiction or abuse. The opioid should be indicated for the pain and prescribed with caution; each case should be assessed individually. Following the recommendations drawn from these guidelines will be important for achieving control of both pain and the accompanying symptoms. The use of major opioids to relieve chronic pain unrelated to cancer, and therefore to improve the quality of life of patients who experience this type of pain, is a legitimate treatment approach.

Pharmacotherapy of low back pain: targeting nociceptive and neuropathic pain components

AIM

To review pharmacological management of chronic low back pain (LBP), with respect to management of nociceptive and neuropathic components.

METHODS

Studies were identified by a PubMed search of English-language papers from the last 10  years, with additional hand searches of relevant reviews.

DISCUSSION

Paracetamol, non-steroidal anti-inflammatory drugs and cyclo-oxygenase-2 inhibitors target the nociceptive component of chronic LBP, and do not affect neuropathic pain mechanisms. Antidepressants target the neuropathic component of chronic LBP; however, conflicting efficacy results have been reported. Opioids target both nociceptive and to a lesser extent neuropathic pain. They are effective in chronic LBP, but many patients require higher doses or combination treatment. The long-term efficacy of opioids in chronic LBP has been questioned because of the absence of high-quality data and concerns regarding tolerability and dependence. The topical preparation lidocaine 5% plaster, indicated in post-herpetic neuralgia, is effective in localized neuropathic pain in patients with chronic LBP. Pregabalin is ineffective as monotherapy for chronic LBP but is effective when combined with celecoxib or opioids. Muscle relaxant monotherapy is ineffective in chronic LBP. Combination therapy is often necessary in patients with chronic LBP, in order to manage both nociceptive and neuropathic pain components.

CONCLUSION

Chronic LBP often comprises both nociceptive and neuropathic components, therefore a multimodal and individualized treatment approach is necessary. Combining drugs with different mechanisms of action (e.g. an agent with µ-receptor activity plus an agent of a different class) represents a rational approach to management of chronic LBP with both nociceptive and neuropathic components.

Routines and rituals: a grounded theory of the pain management of drug users in acute care settings

AIM

This study reviewed the perceptions and strategies of drug users and nurses with regard to pain management in acute care settings.

BACKGROUND

Drug users present unique challenges in acute care settings with pain management noted to be at best suboptimal, at worst non-existent. Little is known about why and specifically how therapeutic effectiveness is compromised.

DESIGN

Qualitative: constructivist grounded theory.

METHOD

A constructivist grounded theory approach incorporating a constant comparative method of data collection and analysis was applied. The data corpus comprised interviews with drug users (n = 11) and five focus groups (n = 22) of nurses and recovering drug users.

RESULTS

Moral relativism as the core category both represents the phenomenon and explains the basic social process. Nurses and drug users struggle with moral relativism when addressing the issue of pain management in the acute care setting. Drug users lay claim to expectations of compassionate care and moralise via narration. Paradoxically, nurses report that the caring ideal and mutuality of caring are diminished. Drug users' individual sensitivities, anxieties and felt stigma in conjunction with opioid-induced hyperalgesia complicate the processes. Nurses' and hospitals' organisational routines challenge drug user rituals and vice versa leading both protagonists to become disaffected. Consequently, key clinical issues such as preventing withdrawal and managing pain are left unaddressed and therapeutic effectiveness is compromised.

CONCLUSION

This study provides a robust account of nurses' and drug users' struggle with pain management in the acute care setting. Quick technological fixes such as urine screens, checklists or the transient effects of (cognitive-based) education (or training) are not the answer. This study highlights the need for nurses to engage meaningfully with this perceptibly 'difficult' group of patients.

RELEVANCE TO CLINICAL PRACTICE

The key aspects likely to contribute to problematic interactions with this patient cohort are outlined so that they can be prevented and, or addressed.

[Perioperative analgesia for opioid tolerant patients]

In this review article the special anesthesiological problems of opioid tolerance and surgical interventions will be presented. These affect patients with a long-term opioid therapy of chronic pain, addicts with long-term substitution therapy and addicts with current or previous heroin addiction ("clean"). For all patient groups a guarantee of continuous and adequate analgesia (avoidance of fear and increasing patient compliance), exploiting suitable regional anesthesia or regional analgesia procedures when possible, and prevention of a physical opioid withdrawal syndrome have utmost priority. The necessary optimization of perioperative pain therapy only succeeds when based on a thorough preoperative examination of the clinical history which subtly inquires into the drug taking habits with respect to opioids and associated medications. Systemic and/or regional analgesia procedures are possible. Regional procedures are more effective for analgesia. Systemic analgesia procedures do not basically differ from those routinely used for patients without opioid tolerance. However, higher doses of opioids are necessary as well as individual titration according to needs. Special conditions apply to patients previously addicted to opioids (clean) when they are to be operated on. Non-opioids are sufficiently effective for low level pain and opiates can be avoided. Opioid therapy with inclusion of a non-opioid is necessary following major operations or for severe postoperative pain, even as i.v. patient-controlled analgesia (i.v. PCA) if needed. For these patients a relapse to addiction can be provoked by insufficient administration of analgesics, not by pain management including opioids.

Impact of opioid rescue medication for breakthrough pain on the efficacy and tolerability of long-acting opioids in patients with chronic non-malignant pain

Background

There is little evidence that short-acting opioids as rescue medication for breakthrough pain is an optimal long-term treatment strategy in chronic non-malignant pain. We compared clinical studies of long-acting opioids that allowed short-acting opioid rescue medication with those that did not, to determine the impact of opioid rescue medication use on the analgesic efficacy and tolerability of chronic opioid therapy in patients with chronic non-malignant pain.

Methods

We searched MEDLINE (1950 to July 2006) and EMBASE (1974 to July 2006) using terms for chronic non-malignant pain and long-acting opioids. Independent review of the search results identified 48 studies that met the study selection criteria. The effect of opioid rescue medication on analgesic efficacy and the incidence of common opioid-related side-effects were analysed using meta-regression.

Results

After adjusting for potentially confounding variables (study design and type of opioid), the difference in analgesic efficacy between the ‘rescue’ and the ‘no rescue’ studies was not significant, with regression coefficients close to 0 and 95% confidence intervals that excluded an effect of more than 18 points on a 0–100 scale in each case. There was also no significant difference between the ‘rescue’ and the ‘no rescue’ studies for the incidence of nausea, constipation, or somnolence in both the unadjusted and the adjusted analyses.

Conclusions

We found no evidence that rescue medication with short-acting opioids for breakthrough pain affects analgesic efficacy of long-acting opioids or the incidence of common opioid-related side-effects among chronic non-malignant pain patients.

Antinociceptive and anti-allodynic effects of 3-alkynyl selenophene on different models of nociception in mice

In this study, antinociceptive and anti-hyperalgesic effects of 3-alkynyl selenophene (3-ASP) were evaluated in mice. Acute toxicity of 3-ASP (1-50 mg/kg, per oral) was investigated in mice. 3-ASP neither caused toxicity nor affects locomotor activity in the rota-rod test. 3-ASP did not change plasma aspartate (AST) and alanine aminotransferase (ALT) activities, urea and creatinine levels. 3-ASP caused a significant increase in tail-immersion and hot-plate response latencies time. 3-ASP inhibited early and late phases of nociception caused by intraplantar (i.pl.) injection of formalin. 3-ASP reduced nociception produced by i.pl. injection of glutamate, bradykinin, phorbol myristate acetate (PMA) and capsaicin in mice. Mechanical hyperalgesia induced by Freund's Complete Adjuvant (CFA) was attenuated by 3-ASP administration to mice (maximal inhibition of 42+/-11%). The anti-hyperalgesic effect of 3-ASP was maintained for up to 6 h. The antinociceptive effect of 3-ASP was not abolished by naloxone (5 mg/kg), discarding the involvement of opioidergic mechanism in this effect. These results indicate that 3-ASP at a dose range of 5-50 mg/kg was especially potent and produced systemic anti-hyperalgesic and antinociceptive actions in mice.

Antinociceptive effect of novel trihalomethyl-substituted pyrazoline methyl esters in formalin and hot-plate tests in mice

The aim of the present study was to evaluate the antinociceptive potential of four novel pyrazoline methyl ester compounds on chemical and thermal models of pain in mice. The following 5-trihalomethylated-4,5-dihydro-1H-pyrazole methyl ester compounds were tested: 3-methyl-5-trifluoromethyl-(MPF3), 4-methyl-5-trifluoromethyl-(MPF4), 3-methyl-5-trichloromethyl-(MPCl3) and 4-methyl-5-trichloromethyl-(MPCl4). MPF3, MPF4, MPCl3 and MPCl4 (0.03-1.0 mmol/kg) given intraperitoneally decreased neurogenic and inflammatory phases of nociception in the formalin test. Moreover, MPF3, MPF4, MPCl3, MPCl4 (0.1-1.0 mmol/kg) and dipyrone (1.5 mmol/kg) also produced a dose-dependent antinociceptive effect in the hot-plate test. However, MPF3, MPF4, MPCl3 and MPCl4 did not impair motor coordination in the rotarod test or spontaneous locomotion in the open field test. The antinociceptive effect of MPF4 (1.0 mmol/kg, i.p.) was reversed by the opioid receptor antagonist naloxone (2 mg/kg, i.p.), but not by the alpha(2)-adrenergic receptor antagonist yohimbine (0.15 mg/kg, i.p.) or by p-chlorophenylalanine ethyl ester (PCPA, 300 mg/kg, i.p.) treatment. In contrast to morphine (5 mg/kg, i.p.), MPF4 given daily for up to 8 days did not generate a tolerance to its antinociceptive effect. However, similar to morphine (11 mg/kg, i.p.), MPF4 reduced gastrointestinal transit in mice. Taken together these results demonstrate that these novel pyrazoline methyl esters tested may be promising prototypes of additional mild analgesics.

Opioid dependence and addiction during opioid treatment of chronic pain

Throughout the long history of opioid drug use by humans, it has been known that opioids are powerful analgesics, but they can cause addiction. It has also been observed, and is now substantiated by multiple reports and studies, that during opioid treatment of severe and short-term pain, addiction arises only rarely. However, when opioids are extended to patients with chronic pain, and therapeutic opioid use is not confined to patients with severe and short-lived pain, compulsive opioid seeking and addiction arising directly from opioid treatment of pain become more visible. Although the epidemiological evidence base currently available is rudimentary, it appears that problematic opioid use arises in some fraction of opioid-treated chronic pain patients, and that problematic behaviors and addiction are problems that need to be addressed. Since the potentially devastating effects of addiction can substantially offset the benefits of opioid pain relief, it seems timely to reexamine addiction mechanisms and their relevance to the practice of long-term opioid treatment for pain. This article reviews the neurobiological and genetic basis of addiction, its terminology and diagnosis, the evidence on addiction rates during opioid treatment of chronic pain and the implications of biological mechanisms in formulating rational opioid treatment regimes.

A molecular basis of analgesic tolerance to cannabinoids

Clinical usage of cannabinoids in chronic pain states is limited by their central side effects and the pharmacodynamic tolerance that sets in after repeated dosage. Analgesic tolerance to cannabinoids in vivo could be caused by agonist-induced downregulation and intracellular trafficking of cannabinoid receptors, but little is known about the molecular mechanisms involved. We show here that the type 1 cannabinoid receptor (CB1) interacts physically with G-protein-associated sorting protein 1 (GASP1), a protein that sorts receptors in lysosomal compartments destined for degradation. CB1-GASP1 interaction was observed to be required for agonist-induced downregulation of CB1 in spinal neurons ex vivo as well as in vivo. Importantly, uncoupling CB1 from GASP1 in mice in vivo abrogated tolerance toward cannabinoid-induced analgesia. These results suggest that GASP1 is a key regulator of the fate of CB1 after agonist exposure in the nervous system and critically determines analgesic tolerance to cannabinoids.

Neural mechanisms of addiction: the role of reward-related learning and memory

Addiction is a state of compulsive drug use; despite treatment and other attempts to control drug taking, addiction tends to persist. Clinical and laboratory observations have converged on the hypothesis that addiction represents the pathological usurpation of neural processes that normally serve reward-related learning. The major substrates of persistent compulsive drug use are hypothesized to be molecular and cellular mechanisms that underlie long-term associative memories in several forebrain circuits (involving the ventral and dorsal striatum and prefrontal cortex) that receive input from midbrain dopamine neurons. Here we review progress in identifying candidate mechanisms of addiction.

Anästhesie und Analgesie bei Suchtpatienten

Addicts have an exaggerated organic and psychological comorbidity and in cases of major operations or polytrauma they are classified as high-risk patients. Additional perioperative problems are a higher analgetics requirement, craving, physical and/or psychological withdrawal symptoms, hyperalgesia and tolerance. However, the clinical expression depends on the substance abused. For a better understanding of the necessary perioperative measures, it is helpful to classify the substances into central nervous system depressors (e.g. heroin, alcohol, sedatives, hypnotics), stimulants (e.g. cocaine, amphetamines, designer drugs) and other psychotropic substances (e.g. cannabis, hallucinogens, inhalants). The perioperative therapy should not be a therapy for the addiction, as this is senseless. On the contrary, the characteristics of this chronic disease must be accepted. Anesthesia and analgesia must be generously stress protective and sufficiently analgesically effective. Equally important perioperative treatment principles are stabilization of physical dependence by substitution with methadone (for heroin addicts) or benzodiazepines/clonidine (for alcohol, sedatives and hypnotics addiction), avoidance of stress and craving, thorough intraoperative and postoperative stress relief by using regional techniques or systematically higher than normal dosages of anesthetics and opioids, strict avoidance of inadequate dosage of analgetics, postoperative optimization of regional or systemic analgesia by non-opioids and coanalgetics and consideration of the complex physical and psychological characteristics and comorbidities. Even in cases of abstinence (clean) an inadequate dosage must be avoided as this, and not an adequate pain therapy sometimes even with strong opioids, can potentially activate addiction. A protracted abstinence syndrome after withdrawal of opioids can lead to increased response to administered opioids (e.g. analgesia, side-effects).

[Psychological pain therapy and opioids -- a contradiction?]

Prescription and accessibility of opioids for patients with non-malignant pain has considerably increased in recent years, and with it the number of patients who, in addition, use psychotherapy. So far no study exists yet on the efficacy, the advantages and disadvantages, or the problem points of this combination of treatments. This issue is of particular importance for interdisciplinary pain management programs as, due to selection biases, they admit a high percentage of patients with psychological distress and simultaneous opioid medication. The questions discussed concern diagnostics, indication, contraindication, and prescription criteria. Patients under distress seem to benefit less from opioids. At the same time, side effects of the medication might influence the psychological interventions negatively (e. g. cognitions or activity). By means of a case report, an example of how the two treatment options can be sensibly combined is presented.

Risikofaktoren für Missbrauch und Abhängigkeit bei der Opioidtherapie chronischer nicht-tumorbedingter Schmerzen

Opioids are valuable analgesics, capable of providing pain relief and functional improvement not only in patients with cancer-related pain, but also in chronic noncancer-related pain patients. However, recent data have shown that the increasing prescription of opioids is associated with a rise in aberrant drug-related behaviour. The causes of this behaviour are multifactorial. Some pharmacotherapeutic, but in particular psychosocial risk and etiologic pain factors have been identified. The indication for the prescription of opioids must be very carefully weighed in the presence of any risk factors. In these cases the integration into a multimodal, interdisciplinary therapy programme is mandatory. A contractual agreement on the opioid therapy including goals, side effects, controls including urine drug testing and criteria to finish the opioid therapy are advisable. Assessment of the progress of therapy is based on the following factors: analgesic efficacy, adverse side effects, functional status and aberrant drug-related behaviour. In the absence of a successful opioid therapy, the treatment must be discontinued to avoid iatrogenic damage, substance abuse and illegal diversion. After discontinuation of the therapy, a comprehensive interdisciplinary re-evaluation is required.