Strategies for the treatment of cancer pain in the new millennium

PRG-1 relieves pain and depressive-like behaviors in rats of bone cancer pain by regulation of dendritic spine in hippocampus

Rationale: Pain and depression, which tend to occur simultaneously and share some common neural circuits and neurotransmitters, are highly prevalent complication in patients with advanced cancer. Exploring the underlying mechanisms is the cornerstone to prevent the comorbidity of chronic pain and depression in cancer patients. Plasticity-related gene 1 (PRG-1) protein regulates synaptic plasticity and brain functional reorganization during neuronal development or after cerebral lesion. Purinergic P2X7 receptor has been proposed as a therapeutic target for various pain and neurological disorders like depression in rodents. In this study, we investigated the roles of PRG-1 in the hippocampus in the comorbidity of pain and depressive-like behaviors in rats with bone cancer pain (BCP). Methods: The bone cancer pain rat model was established by intra-tibial cell inoculation of SHZ-88 mammary gland carcinoma cells. The animal pain behaviors were assessed by measuring the thermal withdrawal latency values by using radiant heat stimulation and mechanical withdrawal threshold by using electronic von Frey anesthesiometer, and depressive-like behavior was assessed by sucrose preference test and forced swim test. Alterations in the expression levels of PRG-1 and P2X7 receptor in hippocampus were separately detected by using western blot, immunofluorescence and immunohistochemistry analysis. The effects of intra-hippocampal injection of FTY720 (a PRG-1/PP2A interaction activator), PRG-1 overexpression or intra-hippocampal injection of A438079 (a selective competitive P2X₇ receptor antagonist) were also observed. Results: Carcinoma intra-tibia injection caused thermal hyperalgesia, mechanical allodynia and depressive-like behaviors in rats, and also induced the deactivation of neurons and dendritic spine structural anomalies in the hippocampus. Western blot, immunofluorescence and immunohistochemistry analysis showed an increased expression of PRG-1 and P2X₇ receptor in the hippocampus of BCP rats. Intra-hippocampal injection of FTY720 or A438079 attenuated both pain and depressive-like behaviors. Furthermore, overexpression of PRG-1 in hippocampus has similar analgesic efficacy to FTY720. In addition, they rescued neuron deactivation and dendritic spine anomalies. Conclusion: The results suggest that both PRG-1 and P2X₇ receptor in the hippocampus play important roles in the development of pain and depressive-like behaviors in bone cancer condition in rats by dendritic spine regulation via P2X₇R/PRG-1/PP2A pathway.

Subanalgesic morphine doses augment fentanyl analgesia by interacting with delta opioid receptors in male rats

Opioids are commonly used for the treatment of postoperative and post-traumatic pain; however, their therapeutic effectiveness is limited by undesirable and life-threatening side effects. Researchers have long attempted to develop opioid co-administration therapies that enhance analgesia, but the complexity of opioid analgesia and our incomplete mechanistic understanding has made this a daunting task. We discovered that subanalgesic morphine doses (100 ng/kg-10 µg/kg) augmented the acute analgesic effect of fentanyl (20 µg/kg) following subcutaneous drug co-administration to male rats. In addition, administration of equivalent drug ratios to naïve rat spinal cord membranes induced a twofold increase in G protein activation. The rate of GTP hydrolysis remained unchanged. We demonstrated that these behavioral and biochemical effects were mediated by the delta opioid receptor (DOP). Subanalgesic doses of the DOP-selective agonist SNC80 also augmented the acute analgesic effect of fentanyl. Furthermore, co-administration of the DOP antagonist naltrindole with both fentanyl-morphine and fentanyl-SNC80 combinations prevented augmentation of both analgesia and G protein activation. The mu opioid receptor (MOP) antagonist cyprodime did not block augmentation. Confocal microscopy of the substantia gelatinosa of rats treated with fentanyl, subanalgesic morphine, or this combination showed that changes in MOP internalization did not account for augmentation effects. Together, these findings suggest that augmentation of fentanyl analgesia by subanalgesic morphine is mediated by increased G protein activation resulting from a synergistic interaction between or heterodimerization of MOPs and DOPs. This finding is of great therapeutic significance because it suggests a strategy for the development of DOP-selective ligands that can enhance the therapeutic index of clinically used MOP drugs.

Palliative Pain Management: When Both Pain and Suffering Hurt

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

Pain: Persistent postsurgery and bone cancer-related pain

The generation of neuropathic pain is a complex dynamic process. Factors involved include one or more dysregulated sensory neural pathways; dysregulated activity of specific neurotransmitters, synapses, receptors and cognitive and emotional neural circuits; and the balance between degenerative and regenerative neural events. Risk factors include age, sex, cognition, emotions, genetic polymorphism, previous or ongoing chronic pain conditions and the use of certain drugs. Intense pain experienced before, during and after surgery is a risk factor for the development of central sensitization with consequent persistent postsurgery neuropathic pain. Blockade of N-methyl-D-aspartate receptors with appropriate drugs during and immediately after surgery may prevent persistent postsurgical pain. Most cancers, but particularly malignant metastases in bone, can induce persistent pain. Local factors including direct damage to sensory nerve fibres, infiltration of nerve roots by cancer cells and algogenic biological agents within the microenvironment of the tumour bring about central sensitization of dorsal horn neurons, characterized by neurochemical reorganization with persistent cancer pain. In this article, the clinical features, pathogenesis and principles of management of persistent postsurgery pain and cancer pain are briefly discussed.

Practical management of opioid rotation and equianalgesia

Purpose

To review the recent literature on opioid rotation (ie, switching from one opioid drug to another or changing an opioid’s administration route) in cancer patients experiencing severe pain and to develop a novel equianalgesia table for use in routine clinical practice.

Methods

The MEDLINE database was searched with terms “cancer pain,” “opioid rotation,” “opioid switching,” “opioid ratio,” “opioid conversion ratio,” and “opioid equianalgesia” for the major opioids (morphine, oxycodone, fentanyl, and hydromorphone) and the intravenous, subcutaneous, oral, and transdermal administration routes. Selected articles were assessed for the calculated or cited opioid dose ratio, bidirectionality, and use of the oral morphine equivalent daily dose or a direct drug-to-drug ratio.

Results

Twenty publications met our selection criteria and were analyzed in detail. We did not find any large-scale, prospective, double-blind randomized controlled trial with robust design, and most of the studies assessed relatively small numbers of patients. Bidirectionality was investigated in seven studies only.

Conclusion

The updated equianalgesic table presented here incorporates the latest data and provides information on bidirectionality. Despite the daily use of equianalgesic tables, they are not based on high-level scientific evidence. More clinical research is needed on this topic.

Pathophysiology and Management of Surgical and Chronic Oral Pain in Dogs and Cats

Pain involves a myriad of physiochemical responses leading to the perception of an unpleasant sensation arising from tissue damage. An understanding of the terminology and basic neurophysiology involved with the pain process is helpful in preventing and treating discomfort in our patients. A general understanding of the concepts of nociception, peripheral sensitization, and central sensitization will allow decisions to be made on the choices of analgesic agents in each individual patient based upon the type, duration, and severity of the pain. Using preemptive pain management with a multimodal approach provides the most consistent and predictable results. Analgesic protocols should be closely scrutinized on an individual basis with careful patient pain assessment during the postoperative period. Chronic pain mechanisms, particularly significant in cancer pain and stomatitis, require aggressive and perhaps unique approaches to ensure maximum patient comfort.

Complementary and alternative medicine in cancer pain management: a systematic review

Quality of life (QoL) encompasses the physical, psychosocial, social and spiritual dimensions of life lived by a person. Cancer pain is one of the physical component has tremendous impact on the QoL of the patient. Cancer pain is multifaceted and complex to understand and managing cancer pain involves a tool box full of pharmacological and non pharmacological interventions but still there are 50-70% of cancer patients who suffer from uncontrolled pain and they fear pain more than death. Aggressive surgeries, radiotherapy and chemotherapy focus more on prolonging the survival of the patient failing to realize that the QoL lived also matters equally. This paper reviews complementary and alternative therapy approaches for cancer pain and its impact in improving the QoL of cancer patients.

(175)Yb-TTHMP as a good candidate for bone pain palliation and substitute of other radiopharmaceuticals

Bone metastasis is one of the most frequent causes of pain in cancer patients. Different radioisotopes such as P-32, Sm-153, Ho-166, Lu-177, and Re-186 with several chemical ligands as ethylenediaminetetramethylene phosphonic acid (EDTMP), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethylene phosphonic acid (DOTMP), and propylenediaminetetramethylene phosphonate (PDTMP) are recommended for bone pain palliation. In this work, (175)Yb-triethylenetetraminehexamethylene phosphonic acid (TTHMP) was produced as a proper alternative to other radiopharmaceuticals. Relatively long half-life (T1/2 = 4.18 days), maximum energy beta particle Eβ =470 keV (86.5%), low abundance gamma emission 396 keV (6.4%), 286 keV (3.01%), 113.8 keV (1.88%) and low cost are considered advantageous of Yb-175 are to wider usage of this isotope; in addition, TTHMP is an ideal carrier moiety for bone metastases. Production, quality control, and biodistribution studies of (175)Yb-TTHMP were targeted. Yb-175 chloride was obtained by thermal neutron bombardment of a natural Yb2O3 sample at Tehran Research Reactor (TRR), radiolabeling was completed in 1 h by the addition of TTHMP at the room temperature and pH was 7.5-8, radiochemical purity was higher than 95%. Biodistribution studies in normal rats were carried out. The results showed favorable biodistribution features of (175)Yb-TTHMP, indicating significant accumulation in bone tissues compared with clinically used bone-seeking radiopharmaceuticals. This research presents (175)Yb-TTHMP can be a good candidate for bone pain palliation and substitute of other radiopharmaceuticals, however, further biological studies in other mammals are still needed.

Effect of dose escalation with single opioid, fentanyl matrix in patients not controlling cancer pain: a multicenter, prospective, observational study in Korea

Purpose

End-of-dose failure (EOD) is a clinically common observation and many cancer patients increase the frequency of opioid administration. Fentanyl matrix use is known to be effective in patients with chronic cancer pain. To measure the effectiveness of increase in a single dose of fentanyl matrix in patients whose pain was not controlled sufficiently, we perform this study.

Materials and Methods

A multi-center, open-label, prospective, observational study was conducted in 30 hospitals in Korea, between August and December 2008.

Results

A total of 452 patients were enrolled; 404 patients completed the study. The mean pain intensity decreased from 5.27 at the first visit to 3.37 at the end of the trial. There was a significant difference in pain intensity (p < 0.001) between the first and last visits. The percentage of pain intensity difference was 30.1%. The prevalence of EOD at the first visit was 73% from the 452 enrolled patients. After the use of fentanyl patch, EOD decreased from 73% to 56%. Pain intensity of patients experiencing EOD was 5.64 at the baseline compared to 4.27 in patients without EOD. On final visit, pain intensity in patients with and without EOD was 4.02 and 2.54, respectively. The observed adverse events were mainly nausea, asthenia, constipation and diarrhea.

Conclusion

This study demonstrated that increasing dose of fentanyl patch decreased pain intensity and decreased the rate of patients experiencing EOD. Thus, fentanyl patch may be an effective modality in cancer patients whose pain was previously not controlled sufficiently; the side effects were as could be expected with an opioid.

An open-label extension study to investigate the long-term safety and tolerability of THC/CBD oromucosal spray and oromucosal THC spray in patients with terminal cancer-related pain refractory to strong opioid analgesics

CONTEXT

Chronic pain in patients with advanced cancer poses a serious clinical challenge. The Δ9-tetrahydrocannabinol (THC)/cannabidiol (CBD) oromucosal spray (U.S. Adopted Name, nabiximols; Sativex(®)) is a novel cannabinoid formulation currently undergoing investigation as an adjuvant therapy for this treatment group.

OBJECTIVES

This follow-up study investigated the long-term safety and tolerability of THC/CBD spray and THC spray in relieving pain in patients with advanced cancer.

METHODS

In total, 43 patients with cancer-related pain experiencing inadequate analgesia despite chronic opioid dosing, who had participated in a previous three-arm (THC/CBD spray, THC spray, or placebo), two-week parent randomized controlled trial, entered this open-label, multicenter, follow-up study. Patients self-titrated THC/CBD spray (n=39) or THC spray (n=4) to symptom relief or maximum dose and were regularly reviewed for safety, tolerability, and evidence of clinical benefit.

RESULTS

The efficacy end point of change from baseline in mean Brief Pain Inventory-Short Form scores for "pain severity" and "worst pain" domains showed a decrease (i.e., improvement) at each visit in the THC/CBD spray patients. Similarly, the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-C30 scores showed a decrease (i.e., improvement) from baseline in the domains of insomnia, pain, and fatigue. No new safety concerns associated with the extended use of THC/CBD spray arose from this study.

CONCLUSION

This study showed that the long-term use of THC/CBD spray was generally well tolerated, with no evidence of a loss of effect for the relief of cancer-related pain with long-term use. Furthermore, patients who kept using the study medication did not seek to increase their dose of this or other pain-relieving medication over time, suggesting that the adjuvant use of cannabinoids in cancer-related pain could provide useful benefit.

Mechanism-based Classification and Physical Therapy Management of Persons with Cancer Pain: A Prospective Case Series

Context:

Mechanism-based classification (MBC) was established with current evidence and physical therapy (PT) management methods for both cancer and for noncancer pain.

Aims:

This study aims to describe the efficacy of MBC-based PT in persons with primary complaints of cancer pain.

Settings and Design:

A prospective case series of patients who attended the physiotherapy department of a multispecialty university-affiliated teaching hospital.

Material and Methods:

A total of 24 adults (18 female, 6 male) aged 47.5 ± 10.6 years, with primary diagnosis of heterogeneous group of cancer, chief complaints of chronic disabling pain were included in the study on their consent for participation The patients were evaluated and classified on the basis of five predominant mechanisms for pain. Physical therapy interventions were recommended based on mechanisms identified and home program was prescribed with a patient log to ensure compliance. Treatments were given in five consecutive weekly sessions for five weeks each of 30 min duration.

Statistical Analysis Used:

Pre–post comparisons for pain severity (PS) and pain interference (PI) subscales of Brief pain inventory-Cancer pain (BPI-CP) and, European organization for research and treatment in cancer-quality of life questionnaire (EORTC-QLQ-C30) were done using Wilcoxon signed-rank test at 95% confidence interval using SPSS for Windows version 16.0 (SPSS Inc, Chicago, IL).

Results:

There were statistically significant (P < 0.05) reduction in pain severity, pain interference and total BPI-CP scores, and the EORTC-QLQ-C30.

Conclusion:

MBC-PT was effective for improving BPI-CP and EORTC-QLQ-C30 scores in people with cancer pain.

Painful decisions for senior pets

Osteoarthritis and cancer are the inevitable consequences of aging and significantly contribute to the cause of death in cats and dogs. Managing the pain associated with these disease states is the veterinarian’s mandate. Many treatment modalities and agents are available for patient management; however, it is only with an understanding of disease neurobiology and a mechanism-based approach to problem diagnosis that the clinician can offer patients an optimal quality of life based on evidence-based best medicine. When treating pain, knowledge is still our best weapon.

Using poison center exposure calls to predict methadone poisoning deaths

Purpose

There are more drug overdose deaths in the Untied States than motor vehicle fatalities. Yet the US vital statistics reporting system is of limited value because the data are delayed by four years. Poison centers report data within an hour of the event, but previous studies suggested a small proportion of poisoning deaths are reported to poison centers (PC). In an era of improved electronic surveillance capabilities, exposure calls to PCs may be an alternate indicator of trends in overdose mortality.

Methods

We used PC call counts for methadone that were reported to the Researched Abuse, Diversion and Addiction-Related Surveillance (RADARS®) System in 2006 and 2007. US death certificate data were used to identify deaths due to methadone. Linear regression was used to quantify the relationship of deaths and poison center calls.

Results

Compared to decedents, poison center callers tended to be younger, more often female, at home and less likely to require medical attention. A strong association was found with PC calls and methadone mortality (b = 0.88, se = 0.42, t = 9.5, df = 1, p<0.0001, R² = 0.77). These findings were robust to large changes in a sensitivity analysis assessing the impact of underreporting of methadone overdose deaths.

Conclusions

Our results suggest that calls to poison centers for methadone are correlated with poisoning mortality as identified on death certificates. Calls received by poison centers may be used for timely surveillance of mortality due to methadone. In the midst of the prescription opioid overdose epidemic, electronic surveillance tools that report in real-time are powerful public health tools.

Clinical characteristics and patterns of healthcare utilization in patients with painful neuropathic disorders in UK general practice: a retrospective cohort study

BACKGROUND

Clinical characteristics and patterns of healthcare utilization in patients with painful neuropathic disorders (PNDs) who are under the care of general practitioners (GPs) in the UK are not well understood.

METHODS

Using a large electronic UK database, we identified all adults (age ≥ 18 years) with any GP encounters between 1 January 2006-31 December 2006 at which a diagnosis of PND was noted ("PND patients"). An age-and gender-matched comparison group also was constituted consisting of randomly selected patients with one or more GP encounters-but no mention of PNDs-during this period. Characteristics and patterns of healthcare utilization of patients in the two groups were then examined over the one-year study period.

RESULTS

The study sample consisted of 31,688 patients with mention of PNDs and an equal number of matched comparators; mean age was 56 years, and 62% were women. The prevalence of various comorbidities was higher among patients in the PND group, including digestive disorders (31% vs. 17% for comparison group), circulatory disorders (29% vs. 22%), and depression (4% vs. 3%) (all p < 0.01). Receipt of prescriptions for pain-related pharmacotherapy also was higher among PND patients, including nonsteroidal anti-inflammatory drugs (56% of PND patients had one or more such prescriptions vs. only 22% in the comparison group), opioids (49% vs. 12%), tricyclic antidepressants (20% vs. 1%), and antiepileptics (12% vs. 1%) (all p < 0.01). PND patients also averaged significantly more GP visits (22.8 vs. 14.2) and referrals to specialists (2.8 vs. 1.4) over one year (both comparisons p < 0.01).

CONCLUSIONS

Patients with PNDs under the care of GPs in the UK have relatively high levels of use of healthcare services and pain-related pharmacotherapy.

Practicability, safety, and efficacy of a "German model" for opioid conversion to oral levo-methadone

INTRODUCTION

An algorithm to convert from any other opioid to oral levo-methadone was developed in Germany, the German model of levo-methadone conversion (GMLC). According to this GMLC, the pre-existing opioid is stopped, then titration of oral levo-methadone is initiated with a starting dose of 5 mg orally q 4 h (plus prn q 1 h). If necessary, levo-methadone dose is increased (pain) or decreased (side effects) by 30% q 4 h (plus prn q 1 h). After 72 h, the achieved single dose is maintained, but the dosing interval increases twofold to q 8 h (plus prn q 3 h). The aim of this study was to obtain information about the practicability, safety, and efficacy of the GMLC in clinical routine.

METHODS

A retrospective, systematic chart review of levo-methadone conversions for the treatment of pain in inpatient palliative care was performed.

RESULTS

Fifty-two patients were analyzed. The dosing interval was increased correctly after 72 h as demanded by the GMLC in 60% of patients. In 85% of the patients, opioid medication with levo-methadone could be maintained until the end of the inpatient stay. In three patients (6%), levo-methadone administration had to be stopped due to side effects. No serious adverse events could be detected during opioid rotation. Pain intensity was reduced significantly (p < 0.001) after conversion concerning mean (NRS 0.9; range 0-4) and maximum pain over the day (NRS 3.9; range 0-10).

CONCLUSION

The presented study indicates that the GMLC provides a practical and reasonably safe approach to perform opioid rotation to levo-methadone in a palliative care setting.

Cancer Pain: A Critical Review of Mechanism-based Classification and Physical Therapy Management in Palliative Care

Mechanism-based classification and physical therapy management of pain is essential to effectively manage painful symptoms in patients attending palliative care. The objective of this review is to provide a detailed review of mechanism-based classification and physical therapy management of patients with cancer pain. Cancer pain can be classified based upon pain symptoms, pain mechanisms and pain syndromes. Classification based upon mechanisms not only addresses the underlying pathophysiology but also provides us with an understanding behind patient's symptoms and treatment responses. Existing evidence suggests that the five mechanisms – central sensitization, peripheral sensitization, sympathetically maintained pain, nociceptive and cognitive-affective – operate in patients with cancer pain. Summary of studies showing evidence for physical therapy treatment methods for cancer pain follows with suggested therapeutic implications. Effective palliative physical therapy care using a mechanism-based classification model should be tailored to suit each patient's findings, using a biopsychosocial model of pain.

Opioid binding sites in human serum albumin

BACKGROUND

Human serum albumin (HSA) is an important carrier for opioids. However, the locations of the binding sites remain unclear. In the present study, we have characterized opioid-HSA interactions using multiple biochemical and biophysical techniques to reveal: (a) the location of the binding site(s); (b) whether naloxone shares the binding site with morphine; and (c) whether opioid agonists share their binding site(s) with general anesthetics.

METHODS

Elution chromatography to determine the global interactions and tryptophan intrinsic fluorescence to determine the localized interactions of opioids with HSA were used. Competition studies using isothermal titration calorimetry were used to determine the overlap of binding site(s) among opioid agonists, antagonists, and general anesthetics. An automatic docking calculation was used to predict the possible binding sites and to assess findings of the solution studies.

RESULTS

For elution chromatography with immobilized HSA, the retention times of naloxone, morphine, and fentanyl were prolonged but shorter than that of propofol. The inhibition of tryptophan fluorescence by naloxone was not affected by morphine or fentanyl. The calorimetric heat profiles of propofol and halothane interaction with HSA were changed significantly, but not equally by morphine, naloxone, or fentanyl. Consistent with direct binding studies, docking results demonstrated that opioids share sites with general anesthetics; a distinct binding site for naloxone was revealed near the sole tryptophan in HSA that is not shared with morphine.

CONCLUSIONS

The interaction of opioids with HSA is weak in comparison with propofol. Naloxone has a distinct binding site in HSA not shared with opioid agonists. Opioids share binding sites with general anesthetics in HSA.

Pharmacological treatment of neuropathic cancer pain: a comprehensive review of the current literature

Neuropathic cancer pain (NCP), commonly encountered in clinical practice, may be cancer-related, namely resulting from nervous system tumor invasion, surgical nerve damage during tumor removal, radiation-induced nerve damage and chemotherapy-related neuropathy, or may be of benign origin, unrelated to cancer. A neuropathic component is evident in about 1/3 of cancer pain cases. Although from a pathophysiological perspective NCP may differ from chronic neuropathic pain (NP), such as noncancer-related pain, clinical practice, and limited publications have shown that these two pain entities may share some treatment modalities. For example, co-analgesics have been well integrated into cancer pain-management strategies and are often used as First-Line options for the treatment of NCP. These drugs, including antidepressants and anticonvulsants, are recommended by evidence-based guidelines, whereas, others such as lidocaine patch 5%, are supported by randomized, controlled, clinical data and are included in guidelines for restricted conditions treatment. The vast majority of these drugs have already been proven useful in the management of benign NP syndromes. Treatment decisions for patients with NP can be difficult. The intrinsic difficulties in performing randomized controlled trials in cancer pain have traditionally justified the acceptance of drugs already known to be effective in benign NP for the management of malignant NP, despite the lack of relevant high quality data. Interest in NCP mechanisms and pharmacotherapy has increased, resulting in significant mechanism-based treatment advances for the future. In this comprehensive review, we present the latest knowledge regarding NCP pharmacological management.

Oxycodone controlled release in cancer pain management

Oral opioids are the treatment of choice for chronic cancer pain. Morphine is the strong opioid of choice for the treatment of moderate to severe cancer pain according to guidelines from the World Health Organization (WHO). This recommendation by the WHO was derived from availability, familiarity to clinicians, established effectiveness, simplicity of administration, and relative inexpensive cost. It was not based on proven therapeutic superiority over other options. Patients who experience inadequate pain relief or intolerable side effects with one opioid may often be successfully treated with another agent or with the same agent administered by a different route. Opioid rotation, or switching to an alternative opioid, helps some patients achieve better pain control with fewer associated adverse effects. Oxycodone is a μ-opioid receptor specific ligand, with clear agonist properties. It is an active potent opioid, which is in part a κ-receptor agonist. Like morphine and other pure agonists, there is no known ceiling to the analgesic effects of oxycodone. The active metabolites of oxycodone (eg, oxymorphone) could be important in oxycodone-mediated analgesia. The main pharmacokinetic difference between oxycodone and morphine is in oral bioavailability. The bioavailability of oxycodone is >60% and the bioavailability of morphine is 20%. Controlled-release oxycodone is absorbed in a bi-exponential fashion. There is a rapid phase with a mean half-life of 37 min, accounting for 38% of the dose, and a slow phase with a half-life of 6.2 h, which accounts for the residual 62%. Oxycodone elimination is impaired by renal failure because there are both an increased volume of distribution and reduced clearance. A lot of studies prove that the efficacy of controlled-release oxycodone in cancer-pain control is at least the same as morphine, immediate-release oxycodone and hydromorphone. Its toxicity profile seems better than that of morphine. There are actually several illustrations of a lower incidence of side-effects in the central nervous system. It is therefore possible to conclude that oxycodone represents a valid alternative to morphine in the management of moderate to severe cancer pain, also as first-line treatment.

Cancer treatment-induced mucositis pain: strategies for assessment and management

Mucositis pain is a major clinical problem associated with cancer treatment. Mucosal tissue injury is a dose-limiting side effect and also limits nutritional intake and oral function, resulting in weight loss and nutritional deficits for many patients. The pathophysiology of mucositis is thought to be a complex array of cytokine-mediated events, which begins with mucosal atrophy and eventually leads to the painful ulceration of the mucosa. This article reviews current research related to pain management for mucositis. Effective treatment for mucositis pain must be targeted at the various factors involved in the pain experience. Although a number of interventions aimed to prevent and treat mucositis have been studied, there is little evidence to recommend any one treatment modality. While current strategies for pain management rely on general treatment for acute pain, research developments are aimed at targeting the specific receptors and enzymes involved in mucositis. As these breakthroughs become available clinically, thorough assessment and timely directed interventions must be implemented in order to limit patient distress from mucositis. This article presents an assessment tool specific to mucositis pain, including physical, functional, and pain parameters.

Experience of newly diagnosed patients with sarcoma receiving chemotherapy

PURPOSE/OBJECTIVES

To examine symptom distress and quality of life (QOL) in newly diagnosed patients with sarcoma receiving chemotherapy.

DESIGN

Pilot study; descriptive, quantitative.

SETTING

Urban community cancer center in the northeastern United States.

SAMPLE

11 newly diagnosed patients with sarcoma.

METHODS

Participants completed the Edmonton Symptom Assessment Scale and the Functional Assessment of Cancer Therapy-General at baseline and on days 1, 15, and 21 of their chemotherapy treatment.

MAIN RESEARCH VARIABLES

Symptom distress and QOL.

FINDINGS

Fatigue was the most prevalent and pervasive symptom. Anxiety, well-being, lack of appetite, drowsiness, and depression were the most commonly reported symptoms during chemotherapy. QOL was negatively affected. The lowest mean score reported was for functional well-being. Outcome profiles for symptom distress increased over time, whereas QOL profiles decreased over time. Exploratory analyses of age, race, sex, and diagnosis group suggested differences that warrant further study.

CONCLUSIONS

Overall, increasing symptom distress and reduced QOL over time were reported by patients with sarcoma during chemotherapy. Exploratory analysis by demographic variables and treatment group suggested the need for further research of predictors for symptom distress and QOL.

IMPLICATIONS FOR NURSING

Clinical and research implications included the need for better understanding about symptom distress and QOL predictors in patients with sarcoma, as well as the evaluation of interventions directed to address this population's specific needs.

Prescription patterns of analgesics in the last 3 months of life: a retrospective analysis of 10202 lung cancer patients

BACKGROUND

To describe the prescription patterns of analgesics during the last 3 months of life in lung cancer and to determine the associated factors.

METHODS

Data on lung cancer patients (N=10,202) who died during 2000-2008 were extracted from the General Practice Research Database (GPRD). This database records prescriptions of patients received from UK general practices (GP), but not those from non-GP routes. Prescription prevalences were estimated. The associated factors were investigated using log-binomial regression.

RESULTS

The overall prescription prevalences were 50.4% (95% confidence interval (CI): 49.4-51.4%) for level 1 (e.g., paracetamol), 34.1% (95% CI: 33.2-35.0%) for level 2 (weak opioids), and 55.5 % (95% CI: 54.5-56.4%) for level 3 analgesics (strong opioids). Prescription prevalence of analgesics of all levels showed an increasing trend over the period 2000-2008 (annual increases range: 1.1-1.5%) but a decreasing trend with age (average decrease per group range: -5.8 to -1.8%). Patients in the older age groups were less likely to be prescribed level 3 analgesics than those in the younger age groups (PR('90+' vs '<50')=0.55 (95% CI: 0.45-0.67); PR('80-89' vs '<50')=0.73 (95% CI: 0.66-0.79); PR('70-79' vs '<50')=0.84 (95% CI: 0.77-0.90)).

CONCLUSION

Analgesics have been increasingly prescribed in lung cancer. However, analgesics, especially at level 3, were relatively under-prescribed to people older than 70 years, warranting further investigation.

Neuropathic pain management in chronic laminitis

Managing pain in horses afflicted by chronic laminitis is one of the greatest challenges in equine clinical practice because it is the dreadful suffering of the animals that most often forces the veterinarian to end the battle with this disease. The purpose of this review is to summarize our current understanding of the complex mechanisms involved in generating and amplifying pain in animals with laminitis and, based on this information, to propose a modified approach to pain therapy. Furthermore, a recently developed pain scoring technique is presented that may help better quantify pain and the monitoring of responses to analgesic treatment in horses with laminitis.

Efficacy and adverse effects of transdermal fentanyl and sustained-release oral morphine in treating moderate-severe cancer pain in Chinese population: a systematic review and meta-analysis

Background

Previous meta-analysis suggested that transdermal fentanyl was not inferior to sustained-release oral morphine in treating moderate-severe cancer pain with less adverse effects. Now, we updated the data and performed a systematic review.

Methods

Updated cohort studies on transdermal fentanyl and oral morphine in the treatment of cancer pain were searched in electronic databases including CBMdisc, CNKI, VIP, Medline, EMBASE and Cochrane Library. Primary end points assessed by meta-analysis were remission rate of pain and incidence of adverse effects. Quality of life was assessed by systematic review, which was the second end point.

Results

32 cohort studies, which included 2651 patients, were included in present study. The remission rate in transdermal fentanyl group and sustained-release oral morphine group were 86.60% and 88.31% respectively, there was no significant difference [RR = 1.13, 95% CI (0.92, 1.38), P = 0.23]. Compared with oral morphine group, there were less adverse effects in terms of constipation [RR = 0.35, 95% CI (0.27, 0.45), P < 0.00001], nausea/vomiting [RR = 0.57, 95% CI (0.49, 0.67), P < 0.00001], and vertigo/somnolence [RR = 0.59, 95% CI (0.51, 0.68), P < 0.00001] in transdermal fentanyl group. Six of selected trials supported either transdermal fentanyl or sustained-release oral morphine improved QOL of cancer patients and one of them showed more patients got better QOL after sustained-release oral morphine transferred to transdermal fentanyl.

Conclusions

Our study showed again that both transdermal fentanyl and oral morphine had the same efficacy in the treatment of moderate-severe cancer pain in Chinese population, but the former might have less adverse effects and better quality of life.

Multicenter, double-blind, randomized, placebo-controlled, parallel-group study of the efficacy, safety, and tolerability of THC:CBD extract and THC extract in patients with intractable cancer-related pain

This study compared the efficacy of a tetrahydrocannabinol:cannabidiol (THC:CBD) extract, a nonopioid analgesic endocannabinoid system modulator, and a THC extract, with placebo, in relieving pain in patients with advanced cancer. In total, 177 patients with cancer pain, who experienced inadequate analgesia despite chronic opioid dosing, entered a two-week, multicenter, double-blind, randomized, placebo-controlled, parallel-group trial. Patients were randomized to THC:CBD extract (n = 60), THC extract (n = 58), or placebo (n = 59). The primary analysis of change from baseline in mean pain Numerical Rating Scale (NRS) score was statistically significantly in favor of THC:CBD compared with placebo (improvement of -1.37 vs. -0.69), whereas the THC group showed a nonsignificant change (-1.01 vs. -0.69). Twice as many patients taking THC:CBD showed a reduction of more than 30% from baseline pain NRS score when compared with placebo (23 [43%] vs. 12 [21%]). The associated odds ratio was statistically significant, whereas the number of THC group responders was similar to placebo (12 [23%] vs. 12 [21%]) and did not reach statistical significance. There was no change from baseline in median dose of opioid background medication or mean number of doses of breakthrough medication across treatment groups. No significant group differences were found in the NRS sleep quality or nausea scores or the pain control assessment. However, the results from the European Organisation for Research and Treatment of Cancer Quality of Life Cancer Questionnaire showed a worsening in nausea and vomiting with THC:CBD compared with placebo (P = 0.02), whereas THC had no difference (P = 1.0). Most drug-related adverse events were mild/moderate in severity. This study shows that THC:CBD extract is efficacious for relief of pain in patients with advanced cancer pain not fully relieved by strong opioids.

The Potential Role of Ketamine in Hospice Analgesia: A Literature Review

OBJECTIVE

The objective of this review is to examine the role of ketamine as an analgesic for palliative treatment in the hospice care setting.

DATA SOURCES

The sources referenced in this review were found September 22, 2005, via an Internet search of the MEDLINE database and Cochrane Database of Systematic Reviews. Search terms included analgesia, cancer pain, dextromethorphan, hospice, ketamine, opioids, palliative care, neuropathic pain, and morphine. Articles and case reports were included that relate to ketamine use as an analgesic agent and not as an anesthetic.

DATA EXTRACTION

Because of patient variability with ketamine use and dosing, focus was placed on analgesic benefit versus no analgesic benefit. Because of the lack of controlled trials, application of all analgesic data related to ketamine use was relevant to this review. The strength of evidence is currently moderate, but the available trials and reports reviewed in this paper describe compelling results.

DATA SYNTHESIS

Ketamine has been effective in producing analgesia in patients receiving palliative care, especially when used in combination with opioids.

CONCLUSION

When opioid therapy is no longer sufficient to improve quality of life in the hospice setting, the addition of ketamine may be considered as adjunctive therapy.

The role of methadone in cancer pain treatment--a review

BACKGROUND

Methadone is an opioid analgesic of step 3 of the World Health Organization (WHO) analgesic ladder.

AIM AND METHODS

To outline pharmacodynamics, pharmacokinetics, drug interactions, equianalgesic dose ratio with other opioids, dosing rules, adverse effects and methadone clinical studies in patients with cancer pain. A review of relevant literature on methadone use in cancer pain was conducted.

RESULTS

Methadone is used in opioid rotation and administered to patients with cancer pain not responsive to morphine or other strong opioids when intractable opioid adverse effects appear. Methadone is considered as the first strong opioid analgesic and in patients with renal impairment. Methadone possesses different pharmacodynamics and pharmacokinetics in comparison to other opioids. The advantages of methadone include multimode analgesic activity, high oral and rectal bioavailability, long lasting analgesia, lack of active metabolites, excretion mainly with faeces, low cost and a weak immunosuppressive effect. The disadvantages include long and changeable plasma half-life, high bound to serum proteins, metabolism through P450 system, numerous drug interactions, lack of clear equianalgesic dose ratio to other opioids, QT interval prolongation, local reactions when administered subcutaneously.

CONCLUSIONS

Methadone is an important opioid analgesic at step 3 of the WHO analgesic ladder. Future controlled studies may focus on establishment of methadone equianalgesic dose ratio with other opioids and its role as the first strong opioid in comparative studies with analgesia, adverse effects and quality of life taken into consideration.

A double-blind, randomized, crossover comparison between single-dose and double-dose immediate-release oral morphine at bedtime in cancer patients

The European Association for Palliative Care guidelines for treatment of cancer pain recommend a double dose (DD) of immediate-release morphine at bedtime instead of single doses (SD) repeated every four hours throughout the night. A previous open controlled study reported more side effects after DD than after SD. The present study was a randomized, double-blind, crossover study comparison of DD and SD of immediate-release morphine during the night, followed by an open pharmacokinetic study. The primary outcome was average pain intensity during the night, as measured on an 11-point numerical rating scale. Secondary outcomes were morning pain, number of rescue medications, adverse effects (nausea, xerostomia, tiredness, sleep quality, and number of awaking episodes) and patient preference. Morphine and metabolites were quantified by a validated liquid chromatography-tandem mass spectrometry method. Nineteen patients completed the clinical study; 13 participated in the pharmacokinetic follow up. Average pain during the night for DD vs. SD was close to statistical significance (mean 0.8 and 1.4, respectively, P=0.058; mean [95% confidence interval] for the difference was 0.50 [0.02, 1.0]). A similar trend was observed for strongest night pain (P=0.069) and sleep quality (P=0.077). Only two patients required rescue morphine. Four patients had no treatment preference; nine and six favored DD and SD, respectively. DD patients displayed higher area under the curve for morphine and morphine-6-glucuronide during the first part of the night. Although DD tended to perform slightly better than SD, a difference in average pain during the night of 0.50 has little clinical significance, and the two procedures are, therefore, clinically equivalent. It is speculated whether the initial higher exposure to morphine-6-glucuronide may have clinical significance.

Clinical and economic characteristics of patients with painful neuropathic disorders in Germany

Using a large database with information from general practitioners (GP) throughout Germany, we identified all adults (age > or = 18 years) with encounters for painful neuropathic disorders (PNDs) between August 1, 2005 and July 31, 2006 (PND patients). We also constituted an age- and sex-matched comparison group, consisting of randomly selected patients without any GP encounters for PNDs during the same period. Selected characteristics were then compared between PND patients and those in the comparison group over the 1-year study period. The study sample consisted of 275,685 PND patients and a similar number in the matched comparison group; mean age was 53.7 years, and 57% were women. PND patients were more likely than matched comparators to have encounters for various comorbidities, including circulatory system disorders (47% vs. 20%, respectively), depression (9% vs. 2%), and anxiety (4% vs. 1%) (all P < 0.01). They also were more likely to have received pain-related medications (57% vs. 13% for comparison group; P < 0.01)--most commonly, nonsteroidal anti-inflammatory drugs, benzodiazepines, and opioids, and less often, tricyclic antidepressants and anti-epileptics. PND patients averaged 7.3 more GP visits during the year (mean [95% CI] = 9.9 [9.9, 9.9] vs. 2.6 [2.6, 2.7] for comparison group); they also had significantly more specialist referrals and physician-excused absences from work (all P < 0.01). Patients with PNDs under the care of GPs in Germany have comparatively more comorbidities and higher levels of use of healthcare services. The pain-related medications that these patients receive raise concerns that PNDs may not be optimally treated in these settings.

Characteristics and patterns of healthcare utilization of patients with fibromyalgia in general practitioner settings in Germany

OBJECTIVE

To examine characteristics and patterns of healthcare utilization of patients with fibromyalgia (FM) under the care of general practitioners (GPs) in Germany.

RESEARCH DESIGN AND METHODS

Retrospective cohort study, using a large electronic database with information on GP encounters in Germany (IMS MediPlus). We identified all patients, aged > or =18 years, with any encounters for FM (ICD-10 diagnosis code M79.7) between February 1, 2004 and January 31, 2007. We also constituted a comparison group consisting of randomly selected patients with one or more GP encounters - but none for FM - during this period, who we matched to FM patients based on age and sex. Characteristics and healthcare utilization of patients in the FM and comparison groups were then examined over the 1-year period, February 1, 2006-January 31, 2007.

MAIN OUTCOME MEASURES

Prevalence of co-morbidities; use of pain-related pharmacotherapy; number of GP office visits; number of specialist referrals; and number of sick notes (physician-excused absences from work).

RESULTS

The study sample consisted of 4983 FM patients and an identical number in the comparison group. Mean age was 58 years; 87% were women. The prevalence of various co-morbidities was greater among FM patients, including painful neuropathies (33% vs. 18% for comparison group) and depression (20% vs. 5%) (both p<0.01); more FM patients also received pain-related pharmacotherapy (67% vs. 28%; p<0.01). Compared with patients in the comparison group, FM patients averaged approximately twice as many GP visits (11.4 [SD=10.1] vs. 5.8 [7.5]), referrals (4.5 [5.2] vs. 2.2 [3.6]), and sick notes (0.6 [1.8] vs. 0.3 [1.1]) (all p<0.01).

LIMITATIONS

Information in the study database is limited to GP encounters, and the sensitivity and specificity of our case-finding methods are unknown.

CONCLUSIONS

Patients with FM under the care of GPs in Germany have comparatively more co-morbidities and higher levels of healthcare utilization.

[Pain management, let us be simple but efficient]

The occurrence of pain during the course of bronchial carcinoma is nearly inescapable and often constitutes the main symptom for patients and those close to them. While pain control is held to be a priority of care in cancerology in the future, this goal is not always reached due to insufficient implementation of recommendations, however widely accessible. Our aim is to present the different aspects of pain treatment through the details of both pharmacological and nonpharmacological means.

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

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

Characteristics and healthcare costs of patients with fibromyalgia syndrome

PURPOSE

To examine the characteristics and healthcare costs of fibromyalgia syndrome (FMS) patients in clinical practice.

MATERIALS AND METHODS

Using a US health-insurance database, we identified all patients, aged > or = 18 years, with any healthcare encounters for FMS (ICD-9-CM diagnosis code 729.1) in each year of the 3-year period, 1 July 2002 to 30 June 2005. A comparison group was then constituted, consisting of randomly selected patients without any healthcare encounters for FMS during this 3-year period. Comparison group patients were matched to FMS patients based on age and sex. Characteristics and healthcare costs of FMS patients and comparison group patients were then examined over the 1-year period, 1 July 2004 to 30 June 2005 (the most recent year for which data were available at the time of the study).

RESULTS

The study sample consisted of 33,176 FMS patients and an identical number in the comparison group. Mean age was 46 years, and 75% were women. FMS patients were more likely to have various comorbidities, including painful neuropathies (23% vs. 3% for comparison group), anxiety (5% vs. 1%), and depression (12% vs. 3%) (all p < 0.001); they also were more likely to have used pain-related pharmacotherapy (65% vs. 34% for comparison group; p < 0.001). Mean (SD) total healthcare costs over 12 months were about three times higher among FMS patients [$9573 ($20,135) vs. $3291 ($13,643); p < 0.001]; median costs were fivefold higher ($4247 vs. $822; p < 0.001).

CONCLUSIONS

Patients with FMS have comparatively high levels of comorbidities and high levels of healthcare utilization and cost.

Clinical use of opioids for cancer pain

Successful management of pain in the cancer patient requires careful assessment of the components of the pain complaint and accurate diagnosis of the cause of pain. Symptomatic management of pain involves pharmacotherapeutic strategies that focus on opioid use. Factors influencing the choice of opioid in patients with cancer pain include the severity of pain, the presence of coexisting disease, response to previous analgesic therapy, pharmacokinetic factors, available formulations, and patient compliance. Long-term opioid prescription always requires individual titration of medication to adequate pain relief, which is determined on an individual patient basis and/or based on manageable adverse effects. Failure to continuously monitor opioid use generally results in overtreatment or undertreatment of pain. The cognitive and psychomotor effects of long-term opioid therapy are not well-defined and merit further study.

Pain Management: A Fundamental Human Right

This article surveys worldwide medical, ethical, and legal trends and initiatives related to the concept of pain management as a human right. This concept recently gained momentum with the 2004 European Federation of International Association for the Study of Pain (IASP) Chapters-, International Association for the Study of Pain- and World Health Organization-sponsored "Global Day Against Pain," where it was adopted as a central theme. We survey the scope of the problem of unrelieved pain in three areas, acute pain, chronic noncancer pain, and cancer pain, and outline the adverse physical and psychological effects and social and economic costs of untreated pain. Reasons for deficiencies in pain management include cultural, societal, religious, and political attitudes, including acceptance of torture. The biomedical model of disease, focused on pathophysiology rather than quality of life, reinforces entrenched attitudes that marginalize pain management as a priority. Strategies currently applied for improvement include framing pain management as an ethical issue; promoting pain management as a legal right, providing constitutional guarantees and statutory regulations that span negligence law, criminal law, and elder abuse; defining pain management as a fundamental human right, categorizing failure to provide pain management as professional misconduct, and issuing guidelines and standards of practice by professional bodies. The role of the World Health Organization is discussed, particularly with respect to opioid availability for pain management. We conclude that, because pain management is the subject of many initiatives within the disciplines of medicine, ethics and law, we are at an "inflection point" in which unreasonable failure to treat pain is viewed worldwide as poor medicine, unethical practice, and an abrogation of a fundamental human right.

Pharmacological strategies for the management of cancer pain in developing countries

Pain associated with cancer is often under treated especially in the developing countries where there are problems of poor economy, poor purchasing power of the citizens, absence of effective national health insurance schemes, poor manpower, fake adulterated and expired drugs, poor drug storage conditions; adverse temperature conditions combined with poor power supply which may affect drug efficacy. There is also poor understanding of the physiopharmacology of cancer pain management by health care providers. Assessment of the severity of the pain by location, oncological type, as well as psychosocial, emotional and environmental factors are necessary. The pain often occurs from malignancy, from procedures done to diagnose, stage and treat the malignancy, and from the toxicities of therapy used in treating the cancer. The first priority of treatment is to control pain rapidly and completely, as judged by the patient. The second priority is to prevent recurrence of pain. Analgesic drugs are given 'by the ladder,' 'by the clock' and 'by the appropriate route' using the analgesic ladder guideline proposed by the World Health Organization (WHO). The pharmacological aspects of various drugs used in the management of cancer pain are discussed.

Orofacial pain in cancer: part II--clinical perspectives and management

Cancer-associated pain is extremely common and is associated with significant physical and psychological suffering. Unfortunately, pain associated with cancer or its treatment is frequently under-treated, probably due to several factors, including phobia of opioids, under-reporting by patients, and under-diagnosis by healthcare workers. The most common etiology of cancer pain is local tumor invasion (primary or metastatic), involving inflammatory and neuropathic mechanisms; these have been reviewed in Part I. As malignant disease advances, pain usually becomes more frequent and more intense. Additional expressions of orofacial cancer pain include distant tumor effects, involving paraneoplastic mechanisms. Pain secondary to cancer therapy varies with the treatment modalities used: Chemo-radiotherapy protocols are typically associated with painful mucositis and neurotoxicity. Surgical therapies often result in nerve and tissue damage, leading, in the long term, to myofascial and neuropathic pain syndromes. In the present article, we review the clinical presentation of cancer-associated orofacial pain at various stages: initial diagnosis, during therapy (chemo-, radiotherapy, surgery), and in the post-therapy period. As a presenting symptom of orofacial cancer, pain is often of low intensity and diagnostically unreliable. Diagnosis, treatment, and prevention of pain in cancer require knowledge of the presenting characteristics, factors, and mechanisms involved.