Discordance between pain specialists and patients on the perception of dependence on pain medication: A multi-centre cross-sectional study

AIM

Patients with chronic non-cancer pain are referred to pain centres to improve their pain treatment. The discontinuation of pain medications in case of poor efficacy can be difficult to accept for patients, particularly opioid analgesics. Previous research has described that from the patients' perspective, the psychological relief of a negative effect of chronic pain and withdrawal symptoms of prescription opioids represent drivers of persistent use and first stage of opioid use disorder, despite insufficient pain relief. There is no validated tool to investigate this psychological dependence. This study aimed to assess discordance between patients and pain specialists in their perception of dependence on pain medication and investigate associations with characteristics of patients, type of pain and iatrogenic pharmacodependence.

METHODS

Self-administered questionnaires (patients and physicians) were administered in six pain centres in France. A question on perceived dependence on pain medications was addressed to the patient and the physician in a matched pair. Discordance between them was evaluated by the Cohen kappa coefficient. Demographics, pain, anxiety and depression, pain medication withdrawal symptoms, diverted use, and craving represented variables studied in a multivariate model as potentially associated with patient-physician discordance.

RESULTS

According to the 212 pairs of completed questionnaires, a perceived dependence was reported by the majority of patients (65.6%) and physicians (68.4%). However, the concordance was fair (kappa=0.38; CI [95%]: 0.25-0.51). Almost all patients (89.3%) were treated with an opioid analgesic. A higher likelihood of discordance was observed when patients suffered from nociplastic pain (odds ratio [OR]: 2.72, 95% [CI]: 1.29-5.84).

CONCLUSION

Medical shared-decision for changing pain treatment could be improved by taking into account the perception of patient dependence on medications for pain relief and or psychoactive effects, particularly in nociplastic pain for which the treatment is challenging.

Real-Life Testing of the Prescription Opioid Misuse Index in French Primary Care

Analgesic opioid (AO) misuse by patients ranges from 0% to 50%. General practitioners are the first prescribers of AO. Our objective was to validate the Prescription Opioid Misuse Index (POMI) in primary care. We conducted a psychometric study in patients with chronic pain who had been taking AOs for at least 3 months and were followed in general practice. Patients responded to the POMI at inclusion and after 2 weeks. The reference used was the DSM-V. Sixty-nine GPs included 160 patients (87 women, 54.4%), mean age 56.4 ± 15.2 years. The total POMI score was 1.50 ± 1.27, and 73/160 (45.6.0%) had a score ≥ 2 (misuse threshold). Internal validity was measured with the Kuder-Richardson coefficient, which was 0.44. Correlations between each item and the total score ranged from 0.06 to 0.35. Test-retest reliability was determined from 145 patients: Lin's concordance coefficient was 0.57 [0.46, 0.68]. Correlation with the DSM-V (Spearman's coefficient) was 0.52. The POMI does not have sufficient psychometric properties to be recommended as a tool to identify the misuse of AOs in primary care. This study clearly showed that there is a need to create a monitoring tool specific to primary care.

Cross-sectional study of the prevalence of prescription opioids misuse in French patients with chronic non-cancer pain: An update with the French version of the POMI scale

Public health issues related to chronic pain management and the risks of opioid misuse and abuse remain a challenge for practitioners. Data on the prevalence of disorders related to the use of prescribed opioids in patients suffering from chronic pain remains rather patchy, in particular because of the absence of a gold standard for their clinical assessment. We estimated the prevalence of prescription opioid misuse (POM), using a specific and validated opioid misuse scale (POMI-5F scale), in adults with chronic non-cancer pain. Nine-hundred-fifty-one (951) patients with opioids prescription and followed-up in pain clinics and addictology centers for chronic non-cancer pain (CNCP) completed the survey interview. The results suggest that 44.4% of participants have POM, accompanied by overuse (42.5%), use of opioids for effects other than analgesia (30.9%), withdrawal syndrome (65.7%), and craving (6.9%). The motivations cited for POM, apart from pain relief, were to calm down, relax and improve mood. POM was shown to be related to male sex (OR 1.52), young age (OR 2.21) and the presence of nociplastic pain (OR 1.62) of severe intensity (OR 2.31), codeine use (OR 1.72) and co-prescription of benzodiazepines (OR 1.59). Finally, despite the presence of three subgroups of misusers, no factor was associated with the intensity of misuse, reinforcing the view that distinguishing between strong and weak opioids is not appropriate in the context of use disorder. Almost half of patients with CNCP misuse their prescribed opioid. Practitioners should be attentive of profiles of patients at risk of POM, such as young, male patients suffering from severe nociplastic pain, receiving prescription for codeine and a co-prescription for benzodiazepine. We encourage French-speaking practitioners to use the POMI-5F scale to assess the presence of POM in their patients receiving opioid-based therapy.

Clinical Trial Registrationclinicaltrials.gov, identifier NCT03195374

eDOL mHealth App and Web Platform for Self-monitoring and Medical Follow-up of Patients With Chronic Pain: Observational Feasibility Study

BACKGROUND

Chronic pain affects approximately 30% of the general population, severely degrades quality of life (especially in older adults) and professional life (inability or reduction in the ability to work and loss of employment), and leads to billions in additional health care costs. Moreover, available painkillers are old, with limited efficacy and can cause significant adverse effects. Thus, there is a need for innovation in the management of chronic pain. Better characterization of patients could help to identify the predictors of successful treatments, and thus, guide physicians in the initial choice of treatment and in the follow-up of their patients. Nevertheless, current assessments of patients with chronic pain provide only fragmentary data on painful daily experiences. Real-life monitoring of subjective and objective markers of chronic pain using mobile health (mHealth) programs can address this issue.

OBJECTIVE

We hypothesized that regular patient self-monitoring using an mHealth app would lead physicians to obtain deeper understanding and new insight into patients with chronic pain and that, for patients, regular self-monitoring using an mHealth app would play a positive therapeutic role and improve adherence to treatment. We aimed to evaluate the feasibility and acceptability of a new mHealth app called eDOL.

METHODS

We conducted an observational study to assess the feasibility and acceptability of the eDOL tool. Patients completed several questionnaires using the tool over a period of 2 weeks and repeated assessments weekly over a period of 3 months. Physicians saw their patients at a follow-up visit that took place at least 3 months after the inclusion visit. A composite criterion of the acceptability and feasibility of the eDOL tool was calculated after the completion of study using satisfaction surveys from both patients and physicians.

RESULTS

Data from 105 patients (of 133 who were included) were analyzed. The rate of adherence was 61.9% (65/105) after 3 months. The median acceptability score was 7 (out of 10) for both patients and physicians. There was a high rate of completion of the baseline questionnaires and assessments (mean 89.3%), and a low rate of completion of the follow-up questionnaires and assessments (63.8% (67/105) and 61.9% (65/105) respectively). We were also able to characterize subgroups of patients and determine a profile of those who adhered to eDOL. We obtained 4 clusters that differ from each other in their biopsychosocial characteristics. Cluster 4 corresponds to patients with more disabling chronic pain (daily impact and comorbidities) and vice versa for cluster 1.

CONCLUSIONS

This work demonstrates that eDOL is highly feasible and acceptable for both patients with chronic pain and their physicians. It also shows that such a tool can integrate many parameters to ensure the detailed characterization of patients for future research works and pain management.

TRIAL REGISTRATION

ClinicalTrial.gov NCT03931694; http://clinicaltrials.gov/ct2/show/NCT03931694.

Prevalence of chronic pain in opioid-maintained patients using the capture-recapture method: a nationwide population-based study

Few studies all based on classical surveys have provided prevalence estimates of chronic pain (CP) in opioid-maintained patients (OMPs) but often had a limited patient sample size and a great variability in the prevalence estimates. This study sought to assess the prevalence of CP in the exhaustive population of OMPs using the capture-recapture method applied to the French nationwide health care database. Capture-recapture methods are increasingly used to estimate the prevalence of chronic conditions but have never been used in the specific context of CP in OMPs. Three large medical-administrative sources were used: the prescription drug database (A-list), the national hospital discharge database (M-list), and the pain center database (C-list). Between 2015 and 2016, 160,429 OMPs aged 15 years and older were identified and age- and sex-matched with 160,429 non-OMPs. All patients treated with analgesic drugs for ≥6 months (A-list) or diagnosed with CP (M- and C-list) were included. Capture-recapture analyses were performed to yield CP estimates with their 95% confidence intervals using log-linear models. In 2015 to 2016, 12,765 OMPs and 2938 non-OMPs with CP were captured. Most patients were male (67%) in OMPs and non-OMPs; median ages for OMPs and non-OMPs were 46 (interquartile range: 38-51) and 48 (41-53) years, respectively. The CP prevalence estimated in OMPs and non-OMPs ranged from 23.6% (14.9-46.2) to 32.1% (28.6-36.3) and from 7.28% (3.98-18.4) to 9.32% (7.42-12.1), respectively. This first study on CP in the exhaustive population of OMPs using the capture-recapture method demonstrated a high prevalence of CP in OMPs, 3- to 4-fold than in the general population.

Analgesic opioid use disorders in patients with chronic non-cancer pain: A holistic approach for tailored management

Chronic pain is a major public health issue that frequently leads to analgesic opioid prescriptions. These prescriptions could cause addiction issues in high-risk patients with associated comorbidities, especially those of a psychiatric, addictive, and social nature. Pain management in dependent patients is complex and is yet to be established. By combining the views of professionals from various specialties, we conducted an integrative review on this scope. This methodology synthesizes knowledge and results of significant practical studies to provide a narrative overview of the literature. The main results consisted in first proposing definitions that could allow shared vocabulary among health professionals regardless of their specialties. Next, a discussion was conducted around the main strategies for managing prescription opioid dependence, as well as pain in the context of opioid dependence and associated comorbidities. As a conclusion, we proposed to define the contours of holistic management by outlining the main guidelines for creating a multidisciplinary care framework for multi-comorbid patients with chronic pathologies.

Dextromethorphan and memantine after ketamine analgesia: a randomized control trial

Purpose

Intravenous ketamine is often prescribed in severe neuropathic pain. Oral N-methyl-D-aspartate receptor (NMDAR) antagonists might prolong pain relief, reducing the frequency of ketamine infusions and hospital admissions. This clinical trial aimed at assessing whether oral dextromethorphan or memantine might prolong pain relief after intravenous ketamine.

Patients and methods

A multicenter randomized controlled clinical trial included 60 patients after ketamine infusion for refractory neuropathic pain. Dextromethorphan (90 mg/day), memantine (20 mg/day) or placebo was given for 12 weeks (n=20 each) after ketamine infusion. The primary endpoint was pain intensity at one month. Secondary endpoints included pain, sleep, anxiety, depression, cognitive function and quality of life evaluations up to 12 weeks.

Results

At 1 month, dextromethorphan maintained ketamine pain relief (Numeric Pain Scale: 4.01±1.87 to 4.05±2.61, p=0.53) and diminished pain paroxysms (p=0.03) while pain intensity increased significantly with memantine and placebo (p=0.04). At 3 months, pain remained lower than at inclusion (p=0.001) and was not significantly different in the three groups. Significant benefits were observed on cognitive-affective domains and quality of life for dextromethorphan and memantine (p<0.05).

Conclusions

Oral dextromethorphan given after ketamine infusion extends pain relief during one month and could help patients to better cope with pain. Future studies should include larger populations stratified on pharmacogenetics screening. Optimization of an oral drug that could extend ketamine antihyperalgesia, with fewer hospital admissions, remains a prime challenge in refractory neuropathic pain.

Prescription opioid analgesic use in France: Trends and impact on morbidity-mortality

BACKGROUND

While data from USA and Canada demonstrate an opioid overdose epidemic, very little nation-wide European studies have been published on this topical subject.

METHODS

Using a nationally representative sample of the French Claims database (>700,000 patients), the exhaustive nationwide hospital discharge database, and national mortality registry, all patients dispensed at least one prescription opioid (PO) in 2004-2017 were identified, to describe trends in PO analgesic use, shopping behaviour, opioid-related hospitalizations and deaths. Annual prevalence of PO use and shopping behaviour (≥1 day of overlapping prescriptions from ≥2 prescribers, dispensed by ≥3 pharmacies) was estimated.

RESULTS

In 2004-2017, the annual prevalence of weak opioid use codeine, tramadol and opium rose by 150%, 123%, and 244%, respectively (p < 0.05). Strong opioid use increased from 0.54% to 1.1% (+104%, p < 0.05), significantly for oxycodone (+1950%). Strong opioid use in chronic noncancer pain rose by 88% (p < 0.05) and 1180% for oxycodone. Opioid shopping increased from 0.50% to 0.67% (+34%, p < 0.05), associated with higher mortality risk HR = 2.8 [95% confidence interval (CI): 1.2-6.4]. Opioid-related hospitalizations increased from 15 to 40 per 1,000,000 population (+167%, 2000-2017), and opioid-related deaths from 1.3 to 3.2 per 1,000,000 population (+146%, 2000-2015).

CONCLUSIONS

This study provided a first European approach to a nationwide estimation with complete access to several national registries. In 2004-2017 in France, PO use excluding dextropropoxyphene more than doubled. The increase in oxycodone and fentanyl use, and nontrivial increasing trend in opioid-related morbidity-mortality should prompt authorities to closely monitor PO consumption in order to prevent alarming increases in opioid-related morbidity-mortality.

SIGNIFICANCE

In 2004-2017, prescription opioid use in France at least doubled and oxycodone use increased particularly, associated with a nontrivial increase in opioid-related morbidity-mortality. Although giving no indication for an 'opioid epidemic,' these findings call for proper monitoring of opioid use.

Milnacipran poorly modulates pain in patients suffering from fibromyalgia: a randomized double-blind controlled study

Introduction

Fibromyalgia is characterized by widespread and chronic pain, and its prevalence is increasing worldwide. Milnacipran, an antidepressant, is often prescribed for fibromyalgia with a possible beneficial effect on central pain modulation. The aim of this study was to evaluate if milnacipran could modify the status of conditioned pain modulation (CPM) in patients suffering from fibromyalgia.

Design and setting

Randomized, double-blind controlled trial.

Subjects and methods

Women with fibromyalgia received milnacipran 100 mg or placebo. The primary end point was the evolution of CPM with treatments after a 30-second painful stimulus. Secondary outcomes included the predictability of milnacipran efficacy from CPM performance, evolution of global pain, mechanical sensitivity, thermal pain threshold, mechanical allodynia, cognitive function, and tolerance.

Results

Fifty-four women with fibromyalgia (46.7±10.6 years) were included and randomized, and 24 patients were analyzed in each group. At inclusion, CPM was dysfunctional (CPM₃₀=-0.5±1.9), and global pain was 6.5±1.8. After treatment, there was a nonsignificant CPM difference between milnacipran and placebo (CPM₃₀=-0.46±1.22 vs -0.69±1.43, respectively, p=0.55) and 18.8% vs 6.3% (p=0.085) patients did reactivate CPM after milnacipran vs placebo. Initial CPM was not a predictor of milnacipran efficacy. Global pain, mechanical and thermal thresholds, allodynia, cognition, and tolerance were not significantly different between both groups.

Conclusion

Milnacipran did not display a significant analgesic effect after 1-month treatment, but the tendency of milnacipran to reactivate CPM in a number of patients must be explored with longer treatment duration in future studies and pleads for possible subtypes of fibromyalgia patients.

Efficacy and safety of a T-type calcium channel blocker in patients with neuropathic pain: A proof-of-concept, randomized, double-blind and controlled trial

BACKGROUND

T-type calcium channels have been shown to play an important role in the initiation and maintenance of neuropathic pain and represent a promising therapeutic target for new analgesic treatments. Ethosuximide (ETX), an anticonvulsant and a T-type channel blocker has shown analgesic effect in several chronic pain models but has not yet been evaluated in patients with neuropathic pain.

METHODS

This proof-of-concept, multicentre, double-blind, controlled and randomized trial compared the efficacy and safety of ETX (given as add-on therapy) to an inactive control (IC) in 114 patients with non-diabetic peripheral neuropathic pain. After a 7-day run-in period, eligible patients aged over 18 years were randomly assigned (1:1) to ETX or IC for 6 weeks. The primary outcome was the difference between groups in the pain intensity (% of change from the baseline to end of treatment) assessed in the intention-to-treat population. This study is registered with EudraCT (2013-004801-26) and ClinicalTrials.gov (NCT02100046).

RESULTS

The study was stopped during the interim analysis due to the high number of adverse events in the active treatment group. ETX failed to reduce total pain and showed a poor tolerance in comparison to IC. In the per-protocol analysis, ETX significantly reduced pain intensity by 15.6% (95% CI -25.8; -5.4) from baseline compared to IC (-7.8%, 95% CI -14.3; -1.3; p = 0.033), but this result must be interpreted with caution because of a small subgroup of patients.

CONCLUSION

Ethosuximide did not reduce the severity of neuropathic pain and induces, at the doses used, many adverse events.

SIGNIFICANCE

This article shows that ETX is not effective to treat neuropathic pain. Nevertheless, per-protocol analysis suggests a possible analgesic effect of ETX. Thus, our work adds significant knowledge to preclinical and clinical data on the benefits of T-type calcium channel inhibition for the treatment of neuropathic pain.

Effect of ketamine combined with magnesium sulfate in neuropathic pain patients (KETAPAIN): study protocol for a randomized controlled trial

Background

Neuropathic pain is difficult to treat, and the efficacy of recommended drugs remains limited. N-methyl-d-aspartate receptors are implicated, and antagonists are a pharmacological option. Ketamine is widely used in French pain clinics, but without consensus or recommendations. Furthermore, the association of ketamine with magnesium has been poorly studied. The aim of the present study is to evaluate the benefit of ketamine with or without magnesium in refractory neuropathic pain.

Methods/design

A randomized, double-blind, crossover, placebo-controlled study will be performed in Clermont-Ferrand University Hospital, Clermont-Ferrand, France. The aim is to evaluate the effect of ketamine with or without magnesium in 22 patients with neuropathic pain. Intravenous ketamine/placebo, ketamine/magnesium sulfate, or placebo/placebo will be administered consecutively to each patient, in random order, once at 5-week intervals. The primary endpoint is the AUC of pain intensity assessed on a 0–10 Numeric Pain Rating Scale for a 5-week period. Data analysis will be performed on an intention-to-treat basis, and all statistical tests (except primary analysis) will be performed with an α risk of 5% (two-sided).

Discussion

Considering the poor efficacy of the drugs available for neuropathic pain, ketamine with or without magnesium sulfate may be a valuable therapeutic option that needs to be standardized.

Trial registration

EudraCT number–2015-000142-29. Registered on April 9, 2015; version 1.4

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2254-3) contains supplementary material, which is available to authorized users.

Incidence of tramadol shopping behavior in a retrospective cohort of chronic non-cancer pain patients in France

PURPOSE

Opioid analgesic use in chronic non-cancer pain (CNCP) is increasingly prevalent, but the benefits and risks are inadequately understood. In France, tramadol is one of the most used prescription opioids, but studies on its misuse liability in CNCP are still lacking. The aim was to assess the incidence of tramadol shopping behavior in CNCP patients and to identify the associated risk factors.

METHODS

A retrospective cohort of CNCP patients aged 18 years and older treated by tramadol for at least six consecutive months between 2005 and 2013 from a sample of the French Health Insurance database was established. Doctor shopping was defined as at least 1 day of overlapping prescriptions written by two or more different prescribers and filled in at least three different pharmacies.

RESULTS

A total of 3505 CNCP patients were included with a majority of women (66.4%) and a mean age of 66.4 ± 14.7 years. The median tramadol treatment duration was 260 [interquartile range: 211-356] days. The 1-year incidence rate of tramadol shopping behavior was 1.0% [95%CI: 0.7-1.5]. On multivariate analysis, risk factors associated with tramadol shopping behavior were age (hazard ratio [HR] = 7.4 [95%CI: 2.8-19.7] for age <40, HR = 2.8 [95%CI: 1.0-7.7] for 40 ≤ age < 50, versus age ≥50), low-income status (HR = 8.5 [95%CI: 3.6-20.5]), and prior use of strong opioids (HR = 5.7 [95%CI: 1.9-17.0]).

CONCLUSION

Tramadol shopping behavior incidence appears low in CNCP patients but may represent a public health concern given the widespread use of tramadol. Education and best monitoring of high-risk patients are needed to reduce doctor shopping. Copyright © 2016 John Wiley & Sons, Ltd.

Rationale and design of a randomized double-blind clinical trial in breast cancer: dextromethorphan in chemotherapy-induced peripheral neuropathy

BACKGROUND

Anti-cancer chemotherapy often induces peripheral neuropathy and consequent cognitive and quality of life impairment. Guidelines recommend antiepileptics or antidepressants but their efficacy is limited.Dextromethorphan, a N-methyl-D-aspartate receptor antagonist, has shown its efficacy in painful diabetic neuropathy and in post-operative pain but has not been studied in chemotherapy-induced peripheral neuropathy. This clinical trial evaluates the effect of dextromethorphan on pain, cognition and quality of life in patients who suffer from neuropathic pain induced by chemotherapy for breast cancer. It also assesses the impact of dextromethorphan genetic polymorphism on analgesia.

METHODS AND DESIGN

This trial is a randomized, placebo-controlled, double-blind clinical study in two parallel groups (NCT02271893). It includes 40 breast cancer patients suffering from chemotherapy-induced peripheral neuropathy. They are randomly allocated to dextromethorphan (maximal dose 90 mg/day) or placebo for 4 weeks. The primary endpoint is pain intensity measured after 4 weeks of treatment on a (0-10) Numeric Pain Rating Scale. Secondary outcomes include assessment of neuropathic pain, cognitive function, anxiety/depression, sleep and quality of life. Data analysis is performed using mixed models and the tests are two-sided, with a type I error set at α=0.05.

DISCUSSION

Considering the poor efficacy of available drugs in chemotherapy-induced neuropathic pain, dextromethorphan may be a valuable therapeutic option. Pharmacogenetics may provide predictive factors of dextromethorphan response in patients suffering from breast cancer.

Median effective dose (ED50) of nefopam and ketoprofen in postoperative patients: a study of interaction using sequential analysis and isobolographic analysis

BACKGROUND

The analgesic efficacy of ketoprofen has been shown after moderate- and severe-pain surgery, and the analgesic efficacy of nefopam has been shown after moderate-pain surgery. The aim of this study was to define the median effective analgesic doses of each drug and to determine whether the interaction of nefopam and of ketoprofen is synergistic.

METHODS

Seventy-two patients scheduled to undergo moderately painful surgery were enrolled in one of three groups. The dose of nefopam and ketoprofen received by a particular patient was determined by the response of the previous patient of the same group, using an up-and-down technique. Initial doses were 18 and 40 mg, with dose adjustment intervals of 2 and 5 mg, in the nefopam and ketoprofen groups, respectively. The initial doses of nefopam and ketoprofen were 8 and 20 mg, respectively, in the nefopam-ketoprofen group, with the same dose adjustment intervals. Analgesic efficacy was defined as a decrease to less than 3 on a 0-10 numeric pain scale, 45 min after the beginning of drug infusion.

RESULTS

The median effective analgesic dose (median value and 95% confidence interval) of nefopam and ketoprofen were, respectively, 28 mg (17-39 mg) and 30 mg (14-46 mg). The median effective analgesic dose of the combination was 1.75 mg (0.9-2.3 mg) for nefopam and 4.3 mg (2.2-6.5 mg) for ketoprofen.

CONCLUSION

The isobolographic analysis demonstrated that the combination of the two drugs produces effective analgesia with an important synergistic interaction.

The Median Effective Dose of Nefopam and Morphine Administered Intravenously for Postoperative Pain After Minor Surgery: A Prospective Randomized Double-Blinded Isobolographic Study of Their Analgesic Action

The aim of this study was to characterize the nature of analgesic interaction between nefopam and morphine administered i.v. for postoperative pain after minor surgery. To do so, we defined the median effective analgesic dose (ED(50)) for each drug and also the median ED(50) of their combination and compared them using the isobolographic method. Determination of median effective doses was performed by the up-and-down sequential drug administration in a two-stage study. First, in a prospective, randomized, double-blinded study, we enrolled 60 patients with mild to moderate pain after minor surgery; this was followed by an open study enrolling 30 patients. The end-point was a pain score less than 3 on a Numerical Pain Scale (0-10). Initial doses were 16 mg in group N, 5 mg in group M, and 7.5 mg of N combined with 2.5 mg of M in group N+M. The testing interval was 2 mg in group N, 1 mg in group M, and 1.5 mg of N combined with 0.5 mg of M in group N+M. ED(50) (95% confidence interval) was 5 mg (4-6 mg) for morphine, 18 mg (16-18 mg) for nefopam, and 4 mg (3.5-4.5 mg) with 12 mg (10.5-13.5 mg) for the combination of morphine and nefopam administered at a 3:1 dose ratio. Isobolographic analysis demonstrated a significant infra-additive interaction. The incidence of side effects did not differ significantly among morphine, nefopam, and their combination. These findings suggest that the combination of nefopam and morphine does not offer any advantage compared to each drug administered i.v. or alone after minor surgery. This study is the first to define the ED(50) of nefopam and morphine in postoperative patients. In conclusion, the addition of nefopam has a morphine-sparing effect, but the combination is infra-additive.

IMPLICATIONS

Pharmacologic interaction between nefopam and morphine shows infra-additivity but their combination may be clinically useful as morphine consumption is decreased in postoperative patients.