Opioid analgesics: comparative features and prescribing guidelines

Comparative Efficacy of Esketamine vs Sufentanil with Propofol for Sedation in EUS: A Randomized, Controlled Study

Purpose

This randomized, controlled trial aimed to assess the sedative effects of esketamine and sufentanil combined with propofol during EUS.

Patients and Methods

Three hundred and forty patients undergone EUS were randomly divided into two groups to receive esketamine 0.25 mg/kg combined with propofol (esketamine group) or sufentanil 0.1 μg/kg combined with propofol (sufentanil group). The primary outcome measure was respiratory depression incidence. The secondary outcomes included the incidence of body movements, propofol dosage, lowest SPO2 during the operation, and management of airway obstruction. In addition, other procedures and anesthesia-related outcomes, and postoperative complications were recorded.

Results

A total of 340 patients underwent randomization. Of these, 172 were assigned to the esketamine group and 168 were assigned to the sufentanil group. 1 patient in the esketamine group was lost in the follow-up. During the EUS, 9 patients (5.3%) in the esketamine group and 26 (15.5%) in the sufentanil group developed respiratory depression; this difference was statistically significant (P = 0.002). Regarding secondary outcomes, the incidence of body movements, induction dosage, supplemental times, and total dosage of propofol were much higher in the sufentanil group than in the esketamine group (P < 0.05). In addition, the lowest SPO2 during the operation, occurrence rate of airway intervention, and management of airway obstruction were significantly different (P < 0.05). Compared to the sufentanil group, the induction time of sedation in the esketamine group was shorter, and the hemodynamics were more stable (P < 0.05). In addition, there were significant differences in the PACU incidence rates of nausea or vomiting between the two groups (P < 0.05), whereas the following day's complications showed no statistical difference.

Conclusion

Esketamine combined with propofol for sedation during EUS can decrease respiratory depression, reduce the dosage of propofol and PONV, and provide a more stable hemodynamic state. Consequently, esketamine could be considered as a potential alternative to sufentanil for sedation during EUS.

Telmisartan Is a Promising Agent for Managing Neuropathic Pain and Delaying Opioid Analgesic Tolerance in Rats

Despite the large arsenal of analgesic medications, neuropathic pain (NP) management is not solved yet. Angiotensin II receptor type 1 (AT1) has been identified as a potential target in NP therapy. Here, we investigate the antiallodynic effect of AT1 blockers telmisartan and losartan, and particularly their combination with morphine on rat mononeuropathic pain following acute or chronic oral administration. The impact of telmisartan on morphine analgesic tolerance was also assessed using the rat tail-flick assay. Morphine potency and efficacy in spinal cord samples of treated neuropathic animals were assessed by [35S]GTPγS-binding assay. Finally, the glutamate content of the cerebrospinal fluid (CSF) was measured by capillary electrophoresis. Oral telmisartan or losartan in higher doses showed an acute antiallodynic effect. In the chronic treatment study, the combination of subanalgesic doses of telmisartan and morphine ameliorated allodynia and resulted in a leftward shift in the dose-response curve of morphine in the [35S]GTPγS binding assay and increased CSF glutamate content. Telmisartan delayed morphine analgesic-tolerance development. Our study has identified a promising combination therapy composed of telmisartan and morphine for NP and opioid tolerance. Since telmisartan is an inhibitor of AT1 and activator of PPAR-γ, future studies are needed to analyze the effect of each component.

Interactions between NSAIDs, opioids and the gut microbiota - Future perspectives in the management of inflammation and pain

The composition of intestinal microbiota is influenced by a number of factors, including medications, which may have a substantial impact on host physiology. Nonsteroidal anti-inflammatory drugs (NSAIDs) and opioid analgesics are among those widely used medications that have been shown to alter microbiota composition in both animals and humans. Although much effort has been devoted to identify microbiota signatures associated with these medications, much less is known about the underlying mechanisms. Mucosal inflammation, changes in intestinal motility, luminal pH and bile acid metabolism, or direct drug-induced inhibitory effect on bacterial growth are all potential contributors to NSAID- and opioid-induced dysbiosis, however, only a few studies have addressed directly these issues. In addition, there is a notable overlap between the microbiota signatures of these drugs and certain diseases in which they are used, such as spondyloarthritis (SpA), rheumatoid arthritis (RA) and neuropathic pain associated with type 2 diabetes (T2D). The aims of the present review are threefold. First, we aim to provide a comprehensive up-to-date summary on the bacterial alterations caused by NSAIDs and opioids. Second, we critically review the available data on the possible underlying mechanisms of dysbiosis. Third, we review the current knowledge on gut dysbiosis associated with SpA, RA and neuropathic pain in T2D, and highlight the similarities between them and those caused by NSAIDs and opioids. We posit that drug-induced dysbiosis may contribute to the persistence of these diseases, and may potentially limit the therapeutic effect of these medications by long-term use. In this context, we will review the available literature data on the effect of probiotic supplementation and fecal microbiota transplantation on the therapeutic efficacy of NSAIDs and opioids in these diseases.

Economic burden of opioid misuse focused on direct medical costs

Background: Since their development, synthetic opioids have been used to control pain. With increased opioid use, problematic opioid prescription has also increased, resulting in a growing economic burden. However, there is a paucity of research studies on the economic burden of prescription opioid misuse in Asia, especially South Korea.

Objectives: To estimate the incremental economic burden of prescription opioid misuse for the South Korean population.

Methods: The National Health Insurance Service-National Sample Cohort database, covering 2% of the South Korean population between 2010 and 2015, was analyzed. Outpatients aged 18 or older who took one or more prescription opioids were selected. Based on their opioid prescription patterns, patients were classified into opioid misuse and non-misuse groups. The direct medical costs per person per year (PPPY) and the incremental economic burden of the opioid misuse group were explored using an exponential conditional model with a suitable distribution and log link function. All analyses were performed using SAS® Enterprise Guide version 9.4, and p < 0.05 was considered statistically significant.

Results: The number of patients who had ≥1 opioid prescription was 345,020 including 84,648 (24.53%) in the opioid misuse group and 260,372 (75.47%) in the non-misuse group. The adjusted mean direct medical costs PPPY were estimated to be USD 401 for the opioid misuse group, which is 1.49 times significantly higher than that for the non-misuse group (p < 0.0001). The incremental economic burden of the opioid misuse group in the South Korean population was estimated to be approximately USD 0.52 billion for the period 2010–2015.

Conclusion: Prescription opioid misuse was significantly associated with the increased economic burden. Along with proper policies for using opioids, it is necessary to monitor opioid prescription patterns to prevent opioid misuse and reduce the related economic burden.

Challenges in anesthesia personalization: resolving the pharmacogenomic puzzle

Clinicians are witnessing differences in the doses required for induction and maintenance of anesthesia, as well as prolonged recovery in some patients. Predictable factors like patient characteristics, factors related to the procedure, pharmacological characteristics of anesthetics and adjunctive drugs, might explain some of the observed differences. However, the role of various polymorphisms of genes encoding for drugs’ molecular targets, transporters and metabolic enzymes can have a significant impact on anesthesia outcome, too. In the present paper, we critically discuss pharmacological characteristics of the most common drugs used in anesthesia, with a focus on the possible genetic background of unpredictable diversities in anesthesia outcomes.

Neurocognitive performance under combined regimens of ketamine-dexmedetomidine and ketamine-fentanyl in healthy adults: A randomised trial

Analgesic doses of ketamine affects neurocognition; however, deficits under co-administration regimens are unknown. This study evaluated the effects of ketamine, alone and in combination with dexmedetomidine or fentanyl on neurocognition. Using a randomised, within-subjects gender stratified design, 39 participants (mean age = 28.4, SD ± 5.8) received a ketamine bolus of 0.3 mg/kg followed by 0.15 mg/kg/h infusion of ketamine (3 h duration). At 1.5 h post-ketamine infusion commencement, participants received either: i) 0.7 μg/kg/h infusion of dexmedetomidine (n = 19) (KET/DEX) or (ii) three 25 μg fentanyl injections over 1.5 h (n = 20) (KET/FENT). Reaction and Movement time (RTI, Simple and 5Choice), Visuospatial Working Memory (SWM) and Verbal Recognition Memory (VRM) were assessed using the Cambridge Neuropsychological Test Automated Battery (CANTAB). Whole blood drug concentrations were determined during ketamine-only infusion, at co-administration (KET/DEX or KET/FENT) and at 2-h post-treatment. Ketamine-only administration impaired psychomotor response speed (Simple and 5Choice) and impaired memory (all p < .001), however did not alter executive function abilities. Independent of sedation, co-administration of dexmedetomidine produced synergistic performance and memory deficits which persisted at post-treatment (KET/DEX) (all p < .001), and were comparatively greater than for KET/FENT (all p < .05). Ketamine, norketamine and dexmedetomidine concentrations were modestly associated with reduced psychomotor speed and accuracy (all p < .05), and an inverse relationship was found between blood concentrations of ketamine, norketamine and dexmedetomidine and performance on memory tasks. Co-administration of ketamine with dexmedetomidine but not with fentanyl exerts synergistic effects on psychomotor performance and memory without executive dysfunction. Assessment of these effects in clinical groups is warranted.

Heterodimerization of Mu Opioid Receptor Protomer with Dopamine D2 Receptor Modulates Agonist-Induced Internalization of Mu Opioid Receptor

The interplay between the dopamine (DA) and opioid systems in the brain is known to modulate the additive effects of substances of abuse. On one hand, opioids serve mankind by their analgesic properties, which are mediated via the mu opioid receptor (MOR), a Class A G protein-coupled receptor (GPCR), but on the other hand, they pose a potential threat by causing undesired side effects such as tolerance and dependence, for which the exact molecular mechanism is still unknown. Using human embryonic kidney 293T (HEK 293T) and HeLa cells transfected with MOR and the dopamine D₂ receptor (D₂R), we demonstrate that these receptors heterodimerize, using an array of biochemical and biophysical techniques such as coimmunoprecipitation (co-IP), bioluminescence resonance energy transfer (BRET¹), Fӧrster resonance energy transfer (FRET), and functional complementation of a split luciferase. Furthermore, live cell imaging revealed that D_2LR, when coexpressed with MOR, slowed down internalization of MOR, following activation with the MOR agonist [D-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO).

Chronic Pain Management in the Elderly

Chronic pain is extremely prevalent in older adults and is associated with significant morbidity, including limited mobility, social isolation, and depressed mood. Pain is defined by a biopsychosocial model highlighting the importance of a multidisciplinary approach to treatment, including multimodal medications, selected interventions, physical therapy and rehabilitation, and psychological treatments. In this narrative review, the authors highlight the use of these approaches in older adults with specific attention paid to considerations unique to aging, including alterations in drug metabolism, avoidance of polypharmacy, and physiologic changes predisposing to painful conditions.

Intrathecal morphine combined with ropivacaine induces spinal myoclonus in cancer patients with an implanted intrathecal drug delivery system: Three case reports

RATIONALE

Although intrathecal opioid infusion has been used for decades for the treatment of severe pain, myoclonus as one of the complications of this therapeutic modality is now beginning to be recognized more.

PATIENTS CONCERNS

Here, we report three patients who developed myoclonus after dose adjustment in intrathecal drug delivery system for the treatment of refractory cancer pain.

DIAGNOSIS

Spinal myoclonus is a sudden, brief, shock-like muscle contractions originating from the central nervous system. In our cases, it occurred after opioid administration via intrathecal delivery system with no abnormality found in laboratory or imaging examinations.

INTERVENTIONS

Spinal myoclonus can be treated effectively by reducing the dose or infusion rate as described in case 1, or changing from an intrathecal to systemic administration in case 2, or correcting infusion and bolus parameters mistakes in case 3.

OUTCOMES

All patients recovered quickly after stopping or decreasing the intrathecal drug infusion.

LESSONS

Prevention is more important than treatment as for spinal myoclonus. Pain management teams should be aware of this distressing complication. Dose of intrathecal drugs should not exceed the recommended maximal daily doses by guidelines and patient education is important for successful intrathecal analgesic therapy.

A Two-Year Prospective Multicenter Study of Opioid Therapy for Chronic Noncancer Pain: Prescription Trends and Predictors

Objectives

Opioid use in chronic pain has increased worldwide in recent years. The aims of this study were to describe the trends and patterns of opioid therapy over two years of follow-up in a cohort of chronic noncancer pain (CNCP) patients and to assess predictors of long-term opioid use and clinical outcomes.

Methods

A prospective cohort study with two years of follow-up was undertaken in four multidisciplinary chronic pain clinics. Demographic data, pain characteristics, and opioid prescriptions were recorded at baseline, three, six, 12, and 24 months.

Results

Six hundred seventy-four CNCP patients were recruited. The prevalence of opioid prescriptions at baseline was 59.6% (N = 402), and 13% (N = 86) were strong opioid prescriptions. At 24 months, opioid prescription prevalence was as high as 74.3% (N = 501), and strong opioid prescription was 31% (N = 207). Most opioid users (71%, N = 479) maintained their prescription during the two years of follow-up. Our opioid discontinuation was very low (1%, N = 5). Opioid users reported higher severity and interference pain scores, both at baseline and after two years of follow-up. Opioid use was independently associated with continuous pain, pain location in the lower limbs, and higher pain interference scores.

Conclusions

This study describes a pattern of increasing opioid prescription in chronic pain patients. Despite the limited improvement of clinical outcomes, most patients keep their long-term opioid prescriptions. Our results underscore the need for changes in clinical practice and further research into the effectiveness and safety of chronic opioid therapy for CNPC.

Obesity has no effect on outcomes following unicompartmental knee arthroplasty

PURPOSE

Although obesity has historically been described as a contraindication to UKA, improved outcomes with modern UKA implant designs have challenged this perception. The purpose of this study was to assess the influence of obesity on the outcomes of UKA with a robotic-assisted system at a minimum follow-up of 24 months with the hypothesis that obesity has no effect on robotic-assisted UKA outcomes.

METHODS

There were 746 medial robotic-assisted UKAs (672 patients) with a mean age of 64 years (SD 11) and a mean follow-up time of 34.6 months (SD 7.8). Mean overall body mass index (BMI) was 32.1 kg/m² (SD 6.5), and patients were stratified into seven weight categories according to the World Health Organization classification.

RESULTS

Patient BMI did not influence the rate of revision surgery to TKA (5.8 %) or conversion from InLay to OnLay design (1.7 %, n.s.). Mean postoperative Oxford knee score was 37 (SD 11) without correlation with BMI (n.s.). The type of prosthesis (InLay/OnLay) regardless of BMI had no influence on revision rate (n.s.). BMI did not influence 90-day readmissions (4.4 %, n.s.), but showed significant correlation with higher opioid medication requirements and a higher number of physical therapy session needed to reach discharge goals (p = 0.031).

CONCLUSION

These findings suggest that BMI does not influence clinical outcomes and readmission rates of robotic-assisted UKA at mid-term. The classic contraindication of BMI >30 kg/m² may not be justified with the use of modern UKA designs or techniques.

LEVEL OF EVIDENCE

IV.

Opioid Equivalency: A Review

Opioid analgesics are often used for the treatment of both acute and chronic pain. These agents can differ in regard to opioid receptor interactions, pharmacological actions, and side effect profiles. Furthermore, an agent can be differentiated by its relative potency and duration of action. This paper highlights the major differences between the opioid analgesics and presents a comparative table which includes equianalgesic doses for available opioid formulations. Also, guidelines for making rational prescribing decisions are discussed.

A period of immobility after remifentanil administration protects from nausea: an experimental randomized cross-over study

Background

The opioid remifentanil induces a decrease of vestibulo-ocular reflex function, which has been associated with nausea and vomiting when the subjects are moved. The study investigates in healthy female volunteers if immobility after remifentanil administration protects from nausea and vomiting.

Methods

In volunteers, a standardized movement intervention (a manually applied head-trunk movement forward, backward and sideward) was started 5 min (session A), 35 min (session B) or 60 min (session C) after cessation of a remifentanil infusion (0.15 μg · kg⁻¹ · min⁻¹). In a cross-over design, 16 participants were randomized to the early (sessions A and B) or the late intervention group (sessions A and C). Nausea was assessed using a 11-point numerical rating scale before and after each movement intervention. Differences within and between groups were assessed with non-parametric tests for paired and unpaired data.

Results

Comparing sessions A, B and C, intensity of nausea was time-dependent after cessation of remifentanil administration (p = 0.015). In the early intervention group, nausea decreased from median 5.0 [IQR 1.5;6.0] in session A to 2.0 [1.0;3.0] in session B (p = 0.094); in the late intervention group nausea decreased from 3.5 [2.0;5.0] in session A to 0.5 [0.0;2.0] in session C (p = 0.031).

Conclusions

In summary, in young healthy women, immobility after remifentanil administration protects from nausea and vomiting in a time-dependent manner. In analogy to motion sickness, opioid-induced nausea and vomiting in female volunteers can be triggered by movement.

Trial registration

German Clinical Trials Register DRKS00010667. The trial was registered retrospectively on June, 20th 2016.

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

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

A Prospective, Randomized, Controlled Trial of Paravertebral Block versus General Anesthesia Alone for Prosthetic Breast Reconstruction

BACKGROUND

Paravertebral blocks have gained popularity because of ease of implementation and a shift toward ambulatory breast surgery procedures. Previous retrospective studies have reported potential benefits of paravertebral blocks, including decreased narcotic and antiemetic use.

METHODS

The authors conducted a prospective controlled trial of patients undergoing breast reconstruction over a 3-year period. The patients were randomized to either a study group of paravertebral blocks with general anesthesia or a control group of general anesthesia alone. Demographic and procedural data, in addition to data regarding pain and nausea patient-reported numeric scores and consumption of opioid and antiemetic medications, were recorded.

RESULTS

A total of 74 patients were enrolled to either the paravertebral block (n = 35) or the control group (n = 39). There were no significant differences in age, body mass index, procedure type, or cancer diagnosis between the two groups. Patients who received a paravertebral block required less opioid intraoperatively and postoperatively combined compared with patients who did not receive paravertebral blocks (109 versus 246 fentanyl equivalent units; p < 0.001), and reported significantly lower pain scores at 0 to 1 (3.0 versus 4.6; p = 0.02), 1 to 3 (2.0 versus 3.2; p = 0.01), and 3 to 6 (1.9 versus 2.7; p = 0.04) hours postoperatively. The study group also consumed less antiemetic medication (0.7 versus 2.1; p = 0.05).

CONCLUSIONS

Incorporating paravertebral blocks carries considerable potential for improving pathways for breast cancer patients undergoing breast reconstruction--with minimal procedure-related morbidity. This is the first prospective study designed to assess paravertebral blocks in the setting of prosthetic breast reconstruction.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, II.

Opioid-induced bowel dysfunction: epidemiology, pathophysiology, diagnosis, and initial therapeutic approach

Opioids affect motor and sensory function throughout the gastrointestinal tract, and are frequently associated with a number of gastrointestinal symptoms including constipation, which impairs the quality of life and may limit the dose of opioid or result in discontinuation altogether. Patients with opioid-induced constipation should be assessed by careful history and physical examination, and in some cases where the diagnosis is unclear with select diagnostic tests. Few clinical studies have been conducted to assess the efficacy of various treatments. However, it is generally recommended that first-line therapy begin with opioid rotation, as well as with low-cost and low-risk approaches such as lifestyle changes, consumption of fiber-rich food, stool softeners, and laxatives.

Informative gene network for chemotherapy-induced peripheral neuropathy

BACKGROUND

Host genetic variability has been implicated in chemotherapy-induced peripheral neuropathy (CIPN). A dose-limiting toxicity for chemotherapy agents, CIPN is also a debilitating condition that may progress to chronic neuropathic pain. We utilized a bioinformatics approach, which captures the complexity of intracellular and intercellular interactions, to identify genes for CIPN.

METHODS

Using genes pooled from the literature as a starting point, we used Ingenuity Pathway Analysis (IPA) to generate gene networks for CIPN.

RESULTS

We performed IPA core analysis for genes associated with platinum-, taxane- and platinum-taxane-induced neuropathy. We found that IL6, TNF, CXCL8, IL1B and ERK1/2 were the top genes in terms of the number of connections in platinum-induced neuropathy and TP53, MYC, PARP1, P38 MAPK and TNF for combined taxane-platinum-induced neuropathy.

CONCLUSION

Neurotoxicity is common in cancer patients treated with platinum compounds and anti-microtubule agents and CIPN is one of the debilitating sequela. The bioinformatic approach helped identify genes associated with CIPN in cancer patients.

Usage of Pain Medications During Stroke Rehabilitation: The Post-Stroke Rehabilitation Outcomes Project (PSROP)

Pain remains one of the most common, yet most challenging, medical problems in health care today, and it is one of the most common complications that occurs after a stroke. Pain can affect the course of stroke rehabilitation adversely, and it occasionally may be a cause for transfer back to an acute care hospital. The Post-Stroke Rehabilitation Outcomes Project (PSROP) database was used to describe the incidence of pain by body location and trends in the use of different classifications of medications to treat pain. Of the 1,122 participants in the PSROP database, the most common locations of pain in stroke survivors were the head, leg, back, and shoulder. The most frequently prescribed classifications of pain medications were other analgesics (acetaminophen and tramadol), followed by narcotic analgesics, non-steroidal antiinflammatory drugs (NSAIDs), anticonvulsants, and tricyclic antidepressants. After acetaminophen, the most frequently prescribed medications in each classification, respectively, include hydrocodone APAP, cox-2 inhibitors, gabapentin, and amitriptyline. Other frequently prescribed pain medications included sumatriptan (migraine analgesic), cyclobenzaprine (muscle relaxant), and baclofen (antispasticity muscle relaxant). Medications should be chosen based upon the medical condition causing pain, the ability of the stroke survivor to comply with administration of the medication, and the cost of the medication. Appropriate and timely treatments of painful conditions result in maximum function and the ability to lead active lives and maintain an adequate quality of life.

Prescription opioid abuse and tampering in the United States: results of a self-report survey

OBJECTIVE

The objective of this study is to estimate the prevalence and impact of prescription opioid abuse and tampering among US adults.

METHODS

Participants from the US National Health and Wellness Survey were invited to complete an online survey assessing use, misuse, and abuse of prescription opioid medications in the preceding 3 months. A total of 25,864 adults were screened for self-reported opioid abuse. Prevalence was calculated using weights based on age, gender, race, and education. Respondents reporting abuse or medical use of prescription opioid medication in the prior 3 months (N = 1,242) completed a questionnaire assessing health care resource use and the Work Productivity and Activity Impairment questionnaire.

RESULTS

The prevalence of prescription opioid abuse in the 3 months prior to the survey was estimated at 1.31% of US adults, with approximately half (0.67%) tampering during that time. Opioid abuse increased with younger age, male sex, minority race, psychiatric illness, alcoholism, cigarette smoking, being employed, and higher household income. Respondents abusing opioid medications reported greater impairment in work and nonwork activities and more health care use than nonusers. Tampering with opioid medication was associated with greater productivity loss and increased use of health care (all P < 0.05).

CONCLUSIONS

Tampering with opioid medications to get high is associated with substantial loss of productivity and health care use. Technologies that reduce users' ability to tamper may reduce the burden of opioid abuse on the health care system.

Transdermal fentanyl patches versus patient-controlled intravenous morphine analgesia for postoperative pain management

Background:

Acute and severe pain is common in patients postoperatively and should be correctly managed. In the past years studies on preparing better postoperative pain control have resulted in development of postoperative pain management guidelines. Perhaps, one of the major improvements in managing postoperative pain is the development of the patient-controlled analgesia systems (PCA), especially through intra venous (IV), extradural and transdermal routes, which has resulted in marked improvements in acute postoperative pain management. Physicians administrate potent opioids for moderate to severe post-surgical pains. Morphine is the most commonly IV-PCA administrated analgesic. The fentanyl iontophoretic transdermal system (fentanyl ITS) is also another efficient option for pain management.

Objectives:

The aim of this study was to compare the analgesic effects of these two routine postoperative pain control systems.

Patients and Methods:

We enrolled 281 patients (224 males, 57 females) in this blind randomized controlled clinical trial, who had undergone an orthopedic surgery, with the mean age of 33.91 ± 14.45 years. Patients were randomly divided into two groups; in group A patients received IV-morphine PCA pump and in group B fentanyl transdermal patches were attached on patients’ arms. The severity of the pain was registered according to Visual Analogue Scale in specially designed forms by pain-trained nurses in two steps; first after the surgery and next before the beginning of analgesic effects. After 24 hours, the pain score was assessed again.

Results:

No significant difference was observed in mean pain intensity score at the first patient assessment. Mean pain intensity scores were also similar in both groups at the last measured time point (P > 0.05). Differential pain intensity scores, showing the impacts of analgesic system on the pain experience of the patients was also similar between fentanyl patches (6.48 ± 2.20) and morphine PCIA (6.40 ± 1.80). (P > 0.05) Mean patient satisfactory score (scale: 0–100) was also similar in both groups (P > 0.05). The percentage of patients, whose differential pain intensity scores at 24 hours reached our pain management goal was similar between fentanyl and morphine groups (P > 0.05). The percentage of patients with at least one adverse event was significantly higher in fentanyl group (P < 0.05). The most frequent adverse events were nausea, vomiting and itching. In none of the groups, no patient experienced serious adverse events related to the studied medications.

Conclusions:

Although both pain killing therapeutic regimens are safe and effective for postoperative pain management, regarding the easy usage of the patches, lower risk of abuse and cost-effectiveness in the Iranian market, it is recommended for use in Iranian hospitals and trauma centers and in countries with similar socioeconomic situations.

Adverse effects associated with non-opioid and opioid treatment in patients with chronic pain

Chronic pain is a debilitating condition that is associated with many common diseases; this places a major burden on the healthcare system. There are currently numerous analgesic agents available for the treatment of chronic pain. In general, the oral non-opioid analgesic, paracetamol, is recommended for the initial treatment of mild to moderate pain. Therapeutic doses of paracetamol do not appear to result in hepatotoxicity, although overdose may lead to acute liver failure. Current data suggest that paracetamol has acceptable gastrointestinal tolerability. Another class of non-opioid analgesic with confirmed efficacy for the treatment of chronic mild to moderate pain are non-steroidal anti-inflammatory drugs (NSAIDs), although this efficacy is offset by the potential of adverse gastrointestinal events. In particular, non-selective NSAIDs, also known as cyclooxygenase (COX) inhibitors, carry an increased risk of serious upper gastrointestinal complications, including ulcers, perforation and bleeding. The introduction of COX-2 inhibitors provided a NSAID-based option with improved gastrointestinal safety, but increased risk of cardiovascular effects. Opioids are powerful analgesic agents used to treat moderate to severe chronic pain. However, treatment with opioids is associated with a number of common adverse effects, including constipation, nausea or vomiting, pruritus, somnolence or cognitive impairment, dry mouth, tolerance or dependence and urinary retention. Although there are multiple strategies in place to manage adverse events that arise from both non-opioid and opioid analgesic therapy, a better understanding of the mechanisms involved in the development of specific drug-related adverse effects is required along with proper prescribing practices and adequate physician/patient education. Balanced against the adverse effects of pain management medications, there is a need to be mindful of the widespread, often serious, adverse consequences of poorly managed pain itself.

Patient considerations in the use of tapentadol for moderate to severe pain

Poorly controlled acute and chronic pain can increase morbidity, impair quality of life and prolong disability. Over 80 percent of post surgical patients report moderate to severe uncontrolled postoperative pain. Over-reliance on potent opioid agonists can lead to several opioid related side effects such as gastrointestinal intolerability, respiratory depression and cognitive impairment. A recently approved dual acting central analgesic tapentadol may offer improved tolerability over traditional opioid agonists while having multimodal opioid and nonopioid analgesic benefits. Tapentadol, classified by the US Food and Drug Administration as a class 2 opioid, is currently marketed in the United States as immediate release (IR) NUCYNTA® for moderate to severe acute pain in tablets of 50 mg, 75 mg, and 100 mg, and as extended release (ER) NUCYNTA ER® for the treatment of chronic moderate to severe pain in tablets of 50 mg, 100 mg, 150 mg, 200 mg, and 250 mg. Tapentadol is a low affinity mu opioid receptor agonist and a norepinephrine reuptake inhibitor. Tapentadol has no active metabolites and this property makes it useful in patients with hepatic and renal failure. Clinical trials with tapentadol IR showed that there was improved gastrointestinal tolerability and similar pain relief as compared to oxycodone IR. Tapentadol ER allows for twice daily dosing. Clinical trials showed that tapentadol ER could effectively relieve moderate to severe chronic pain and was associated with significantly fewer gastrointestinal adverse effects as compared to oxycodone controlled release. Tapentadol ER is indicated and has Food and Drug Administration approval for the treatment of chronic painful diabetic neuropathy. The most common side effects of tapentadol are nausea (30%), vomiting (18%), dizziness (24%), and somnolence (15%). Tapentadol, due to its potential synergistic effects on norepinephrine levels, is contraindicated in patients who have taken monoamine oxidase inhibitors within the last 14 days. Caution has to be exercised with the use of tapentadol IR and tapentadol ER in the presence of other central nervous system depressants such as neuroleptics, opioids, illicit drugs, muscle relaxants, sedatives, and anxiolytics.

Quality assessment of the methods used in published opioid conversion reviews

The study objective was to assess methodological quality of opioid conversion systematic reviews. The electronic databases PubMed, EMBASE, and Scopus were used to identify the systematic reviews from the earliest available date until April 2012. Studies were not restricted based on type of opioid, country, or languages. Methodological quality was evaluated using the "Assessment of Multiple Systematic Reviews (AMSTAR)." A total of 2772 articles were found from which five met inclusions criteria. No review mentioned about the duplicate study selection and data extraction. Two reviews included a list of studies that were excluded studies. One study did not provided information on the characteristics of primary studies that were included. Of the three reviews that evaluated the quality of primary studies, two used the quality of included studies in formulating conclusions. Only two reviews provided information about conflicts of interest. Of the five included systematic reviews, three reached a moderate score; two had poor quality. Specific recommendations to improve methodological quality would include performing the data selection and extraction in duplicate, listing or showing the flowchart of studies that were included and excluded along with the reasons, including the main studies data illustrating tables, and including an assessment of the quality of the primary included studies.

Nerve growth factor-mediated regulation of pain signalling and proposed new intervention strategies in clinical pain management

Nerve growth factor (NGF) is the founding member of the neurotrophins family of proteins. It was discovered more than half a century ago through its ability to promote sensory and sympathetic neuronal survival and axonal growth during the development of the peripheral nervous system, and is the paradigmatic target-derived neurotrophic factor on which the neurotrophic hypothesis is based. Since that time, NGF has also been shown to play a key role in the generation of acute and chronic pain and in hyperalgesia in diverse pain states. NGF is expressed at high levels in damaged or inflamed tissues and facilitates pain transmission by nociceptive neurons through a variety of mechanisms. Genetic mutations in NGF or its tyrosine kinase receptor TrkA, lead to a congenital insensitivity or a decreased ability of humans to perceive pain. The hereditary sensory autonomic neuropathies (HSANs) encompass a spectrum of neuropathies that affect one's ability to perceive sensation. HSAN type IV and HSAN type V are caused by mutations in TrkA and NGF respectively. This review will focus firstly on the biology of NGF and its role in pain modulation. We will review neuropathies and clinical presentations that result from the disruption of NGF signalling in HSAN type IV and HSAN type V and review current advances in developing anti-NGF therapy for the clinical management of pain.

Modulation of nociception by social factors in rodents: contribution of the opioid system

RATIONALE

The opioid system is involved in the regulation of several behavioral and physiological responses, controlling pain, reward, and addictive behaviors. Opioid administration, depending on drugs and doses, usually affects sociability reducing interactions between conspecifics, whereas some affiliative behaviors such as sexual activity, social grooming, and play behavior increase the endogenous opioid activity.

OBJECTIVES

The possible interaction between endogenous opioids released during socio/sexual behavior and their analgesic effect on pain response is reviewed in the rodent literature.

RESULTS

Direct evidence for socially mediated opioid changes resulting in increase in nociceptive threshold derives from studies exploring the effects of defeat experiences, social isolation, maternal, sexual behavior, and social reunion among kin or familiar animals in laboratory rodents. Indirect evidence for endogenous activation of the opioid system, possibly affecting pain sensitivity, derives from studies investigating the relevance of natural social reward using the conditioned place preference protocols or analyzing ultrasonic vocalizations associated to positive affective contexts. Finally, genetic and epigenetic factors that affect the opioid system during development are reported to be involved in modulating the response to social stimuli as well as nociception.

CONCLUSIONS

All studies highlight the relevance of affiliative contact behavior between conspecifics that is responsible for the activation of the endogenous mu-opioid system, inducing nociceptive threshold increase.

Clinical efficacy and safety of tapentadol immediate release in the postoperative setting

The appropriate treatment for postoperative pain remains a common dilemma for podiatric surgeons and patients undergoing surgery of the foot and ankle. The treatment of moderate to severe acute pain typically relies heavily on the use of opioid analgesics, such as hydrocodone and oxycodone, which are often associated with adverse effects, including nausea and vomiting. These adverse effects may have a negative impact on postoperative outcomes and reduce patient compliance with analgesic therapy. Tapentadol is a novel, centrally acting analgesic with two mechanisms of action--μ-opioid receptor agonism and norepinephrine reuptake inhibition--in a single molecule. Tapentadol immediate release has been evaluated in a series of clinical trials in patients with postoperative pain after bunionectomy. The results of these studies demonstrate that tapentadol immediate release is associated with an improved gastrointestinal tolerability profile relative to oxycodone immediate release at doses providing comparable analgesia. Therefore, tapentadol immediate release may offer an improved analgesic option for the relief of postoperative pain after podiatric surgery.

Examination of the interaction between peripheral lumiracoxib and opioids on the 1% formalin test in rats

It has been shown that the association of non-steroidal anti-inflammatory drugs (NSAIDs) with opioid analgesic agents can increase their antinociceptive activity, allowing the use of lower doses and thus limiting side effects. Therefore, the aim of the present study was to examine the possible pharmacological interaction between lumiracoxib and codeine or nalbuphine at the local peripheral level in the rat using the 1% formalin test and isobolographic analysis. Lumiracoxib, codeine, nalbuphine or fixed-dose ratios lumiracoxib-codeine or lumiracoxib-nalbuphine combinations were administrated locally in the formalin-injured paw and the antinociceptive effect was evaluated using the 1% formalin test. All treatments produced a dose-dependent antinociceptive effect. ED(40) values were estimated for the individual drugs and an isobologram was constructed. The derived theoretical ED(40)'s for the lumiracoxib-codeine and lumiracoxib-nalbuphine combinations were 423.4+/-31.3 microg/paw and 310.9+/-24.2 microg/paw, respectively, being significantly higher than the actually observed experimental ED(40) values, 233.2+/-30.9 microg/paw and 132.7+/-11.6 microg/paw, respectively. These results correspond to a synergistic interaction between lumiracoxib and opioids at the local peripheral level, potency being about two times higher with regard to that expected from the addition of the effects of the individual drugs. Data suggest that low doses of the lumiracoxib-opioids combination can interact synergistically at the peripheral level and therefore this drug association may represent a therapeutic advantage for the clinical treatment of inflammatory pain.

Prospective randomized study of two surgical approaches for total hip arthroplasty

The benefits of different surgical approaches for total hip arthroplasty continue to be debated. One hundred patients were prospectively enrolled and randomized into 2 groups. One group underwent total hip arthroplasty through a single-incision modified Smith-Peterson approach, whereas the other group underwent total hip arthroplasty through a direct lateral approach. All patients received the same postoperative protocol. Evaluation included operative time, estimated blood loss, analgesia requirement, transfusions, and length of stay. Functional outcome was assessed preoperatively and postoperatively. Up to 1-year follow-up, the direct anterior group demonstrated significantly better improvement in both the mental and physical health dimensions of Short Form-36 and Western Ontario McMaster Osteoarthritis Index compared with direct lateral approach group. At 2 years, the results in both groups were the same.

Review of the effect of opioid-related side effects on the undertreatment of moderate to severe chronic non-cancer pain: tapentadol, a step toward a solution?

OBJECTIVE

Opioids are among the most effective and potent analgesics currently available. Their utility in the management of pain associated with cancer, acute injury, or surgery is well recognized. However, extending the application of opioids to the management of chronic non-cancer pain has met with considerable resistance. This resistance is due in part to concerns related to gastrointestinal and central nervous system-related adverse events as well as issues pertaining to regulatory affairs, the development of tolerance, incorrect drug usage, and addiction. This review focuses on the incidence of opioid-related side effects and the patient and physician barriers to opioid therapy for chronic non-cancer pain. Tapentadol, a centrally acting analgesic with two mechanisms of action, micro-opioid agonism and norepinephrine reuptake inhibition, may be considered to be a partial solution to some of these issues.

METHODS

MEDLINE was searched for English-language articles from 1950 to February 2010 using the terms chronic non-cancer pain and opioids together and in combination with undertreatment, adherence, and compliance.

RESULTS

The majority of patients treated with traditional opioids experience gastrointestinal- or central nervous system-related adverse events, most commonly constipation, nausea, and somnolence. These side effects often lead to discontinuation of opioid therapy. Concerns about side effects, analgesic tolerance, dependence, and addiction limit the use of opioids for the management of chronic pain. Treatment with tapentadol appears to provide several advantages of an analgesic with a more favorable side-effect profile than the classic micro-opioid receptor agonist oxycodone (especially related to gastrointestinal tolerability).

CONCLUSIONS

The pervasiveness of opioid-associated side effects and concerns related to tolerance, dependence, and addiction present potential barriers to the approval and use of opioids for the management of chronic non-cancer pain. The lower incidence of opioid-associated adverse events and possibly fewer withdrawal symptoms, combined with a satisfactory analgesic profile associated with tapentadol, suggest its potential utility for the management of chronic non-cancer pain. This review will focus on the incidence of opioid-related side effects and barriers to opioid therapy that are available as English-language articles in the MEDLINE index, and as such, it is a representative but not an exhaustive review of the current literature.

Dilemmas in chronic/persistent pain management

The burden of chronic/persistent pain is substantial for the patient and society as a whole. Although a variety of pharmacologic treatments are available, chronic/persistent pain remains inadequately treated. Many pharmacologic treatment options provide analgesic efficacy for 4 to 6 hours, requiring multiple doses for continuous pain relief. The inconvenience of multiple doses may prevent many patients from achieving adequate pain relief. Other limitations to the current pharmacologic treatment options include gastrointestinal effects, cardiovascular effects, and organ toxicity, as well as fear of abuse or addiction. The purpose of this review is to highlight the burden of chronic/persistent pain in today's society and discuss the limitations of short-acting pharmacologic therapies used in the treatment of chronic/persistent pain.

Ester prodrugs of morphine improve transdermal drug delivery: a mechanistic study

Two alkyl esters of morphine, morphine propionate (MPR) and morphine enanthate (MEN), were synthesized as potential prodrugs for transdermal delivery. The ester prodrugs could enhance transdermal morphine delivery. The mechanisms of this enhancing effect were elucidated in this study. Both prodrugs were more lipophilic than their parent drug as evaluated by the skin/vehicle partition coefficient (log P) and capacity factor (log K′). The in-vitro skin permeation of morphine and its prodrugs from pH 6 buffer was in the order of MEN &gt; MPR &gt; morphine. MPR and MEN respectively enhanced the transdermal delivery of morphine by 2- and 5-fold. A contrary result was observed when using sesame oil as the vehicle. The prodrugs were stable against chemical hydrolysis in an aqueous solution, but were readily hydrolysed to the parent drug when exposed to skin homogenate and esterase. Approximately 98% MPR and ∼75% MEN were converted to morphine in an in-vitro permeation experiment. The viable epidermis/dermis contributed to a significant resistance to the permeation of ester prodrugs. According to the data of skin permeation across ethanol-, α-terpineol-, and oleic acid-pretreated skin, MEN was predominantly transported via lipid bilayer lamellae in the stratum corneum. The intercellular pathway was not important for either morphine or MPR permeation.

Chemotherapy-induced peripheral neuropathy as a predictor of neuropathic pain in breast cancer patients previously treated with paclitaxel

Neuropathic pain (NP) remains difficult to control for a significant number of patients with cancer. Chemotherapy-induced peripheral neuropathy (CIPN) has been postulated as an initial stage in the development of NP. To assess whether CIPN (defined as National Cancer Institute Common Toxicity Criteria grade 2 or higher) was associated with NP, we conducted a survey of breast cancer patients who had participated in clinical trials of paclitaxel. Of the 430 potential respondents, 240 responded to the survey. Results showed that 64% experienced CIPN during paclitaxel treatment. Follow-up survey data revealed that 27% of those with CIPN were subsequently diagnosed with NP. Logistic regression analyses showed that those who had experienced CIPN were 3 times more likely to develop NP (95% confidence interval = 1.2-7.2; P < .001), which persisted in the multivariate logistic model. In addition, NP patients reported twice as many visits to their health care provider (P = .02) and had taken more prescription (50% vs 19%; P = .001) and over-the-counter medications (62.5% versus 45%; P = .08) for pain than those without NP. The results of this study confirm that CIPN is a predictor of NP, suggesting that survivors treated with paclitaxel should be regularly monitored for NP beyond treatment.

PERSPECTIVE

The survival rates of breast cancer patients have steadily improved over recent years; thus, research into symptoms that persist after treatment is important. We found CIPN as a predictor of NP. Understanding the epidemiology of NP in breast cancer patients has high clinical and public health significance.

Cognition following computer-assisted total knee arthroplasty: a prospective cohort study

BACKGROUND

A substantial number of patients experience postoperative cognitive changes following total joint arthroplasty. The change in mental status may be the result of fat and bone-marrow-debris embolization. We hypothesized that the use of computer-assisted total knee arthroplasty, which does not involve the use of intramedullary alignment rods, would produce less fat and bone-marrow-debris embolization and, hence, fewer changes in mental status.

METHODS

Forty-seven patients who underwent total knee arthroplasty with use of a computer-assisted navigation system and forty-eight patients who underwent conventional total knee arthroplasty without the assistance of computer navigation were followed prospectively. The validated Folstein Mini-Mental State Examination (MMSE) was used to assess the mental status of the patients. The test was administered preoperatively, serially postoperatively while the patient was in the hospital, and at six months. Medication and oxygen requirements were recorded.

RESULTS

On the basis of the numbers studied, no significant differences in postoperative pain-medication or oxygen requirements were found between the group treated with computer-assisted navigation (the navigation group) and the group treated with conventional total knee arthroplasty (the control group). The mean postoperative MMSE score was 88.9 points in the navigation group and 89.3 points in the control group (p = 0.844). Twenty-five patients in the navigation group and thirty-six patients in the control group completed the test at six months. The mean score at that time was 95.3 points in the navigation group and 96.3 points in the control group (p = 0.514).

CONCLUSIONS

Further research is needed to determine if fat and bone-marrow-debris embolization is truly decreased by the use of computer-assisted total knee arthroplasty and if such a reduction has any clinical relevance.

Opioid switching and rotation in primary care: implementation and clinical utility

BACKGROUND

Opioid therapy is the standard treatment for moderate-to-severe cancer pain and is becoming a more frequent treatment for moderate-to-severe chronic noncancer pain. Response to opioids varies significantly between patients and even within the individual patient at different stages of treatment. Finding an opioid at a dose that provides adequate long-term analgesia with minimal adverse effects can be difficult. Opioid switching and opioid rotation, at different stages of therapy, represent two clinical strategies used to optimize opioid response for patients with moderate-to-severe pain.

OBJECTIVES

Review the theoretical and clinical evidence supporting the concepts of opioid switching and rotation, outline the conditions under which these practices should be considered, and briefly suggest practical steps for their implementation.

SCOPE

Clinical literature, clinical practice and guideline databases, and professional society websites were searched for articles or reports describing opioid switching or opioid rotation in chronic pain therapy; variability in patient response to opioid therapy; physiologic, pharmacologic, and genetic factors that affect clinical response to opioids; and practical approaches to maximizing analgesia and minimizing adverse effects in opioid therapy. It is outside the scope of this review to evaluate the pharmacoeconomic aspects that affect changes in opioid therapy.

FINDINGS

The variability in de novo clinical response to opioids likely represents the interaction of the varying properties of the individual opioids with the variability in individual patient biology. This interaction forms the rationale for opioid switching and explains its clinical utility. As with opioid switching, success with opioid rotation is related to the myriad of factors determining an individual patient's response to a specific opioid. However, the benefits of opioid rotation also derive from a partial reversal of tolerance at the mu-opioid receptor and the response of different micro-opioid receptor subtypes to the different opioids.

A new extended release formulation (OROS) of hydromorphone in the management of pain

Opioid analgesics are essential in the treatment of moderate to severe cancer-related pain. Opioids are also recognized as important in the management of other severe, persistent refractory painful conditions, such as sickle cell disease and arthritis. In the clinical practice of pain management, stable opioid dosing generally depends on achieving maximal analgesia with tolerable side effects typical of opioid analgesics. There is a wide interindividual variability of responsiveness to exogenous opioids both in terms of analgesic efficacy and side effects. Optimizing pain management for the individual patient may require sequential trials of opioid medications until the regimen with the most favorable therapeutic ratio of efficacy to side effects is determined.

Behavioral and neurochemical changes induced by oxycodone differ between adolescent and adult mice

Nonmedical use of the prescription opioid analgesic oxycodone is a major problem in the United States, particularly among adolescents and young adults. This study characterized self-administration of oxycodone by adolescent and adult mice, and how this affects striatal dopamine levels. Male C57BL/6J mice (4 or 10 weeks old) were allowed to acquire oxycodone self-administration (0.25 mg/kg per infusion) for 9 days, and then tested with varying doses of oxycodone (0, 0.125, 0.25, 0.5, and 0.75 mg/kg per infusion). On completion of the self-administration study, a guide cannula was implanted into the striatum of these mice. Six days later, microdialysis was conducted on the freely moving mouse. After collection of baseline samples, oxycodone was administered i.p. (1.25, 2.5, and 5.0 mg/kg) and samples were collected for 1 h after each dose. Adult mice self-administered significantly more oxycodone across the doses tested. After 1 week, basal striatal dopamine levels were lower in mice of both ages that had self-administered oxycodone than in yoked saline controls. Oxycodone challenge increased striatal dopamine levels in a dose-dependent manner in both age groups. Of interest, the lowest dose of oxycodone led to increased striatal dopamine levels in the mice that had self-administered oxycodone during adolescence but not those that self-administered it as adults. The lower number of infusions of oxycodone self-administered by adolescent mice, and their later increased striatal dopamine in response to the lowest dose of oxycodone (not found in adults), suggest differential sensitivity to the reinforcing and neurobiological effects of oxycodone in the younger mice.

Opioids for nonmalignant pain

Pain is the most common symptom in the world for which patients seek professional help. Opioids offer an appropriate and safe treatment for some but not all patients with nonmalignant chronic pain. Potential risks, including drug abuse and intolerable side effects, appear to be manageable or even preventable in most cases. Patients with persistent rheumatic pain who have failed traditional treatments should be considered for long-acting opioids. Opioids are best administered in the framework of weighing the good against the bad in each patient, recognizing the potential morbidity and sometimes mortality in untreated patients who have severe and disabling pain daily.

Safety evaluation of Elixir paregorico® in healthy volunteers: a phase I study

A liquid alcoholic extract of Papaver somniferum named Elixir Paregorico® is extensively used for diarrheal diseases in Brazil. Its increased popularity has brought concerns and fears over the safety of this herbal product. Given the lack of investigative clinical studies, in this regard, this study investigated whether Elixir Paregorico® administration causes any noticeable toxic effects in healthy volunteers. In all, 28 middle-aged healthy male ( n = 14) and female ( n = 14) were enrolled. After screening and a washout period, eligible subjects received four oral doses per day of Elixir Paregorico® (3 mL diluted in 30 mL of water) over a 10-day period. Altogether, all 28 participants completed the study. The results of hematological and biochemical tests performed pre and post-treatment were within the normal range. In both male and female volunteers, there were no statistical differences ( P > 0.05) in the results of clinical and laboratory tests performed at screening, on 5th and 10th day visits, and at final assessment. Although mild adverse events were related, which subsided spontaneously, no serious untoward reactions were reported following Elixir Paregorico® administration. To our knowledge, this is the first demonstration that Elixir Paregorico® administered four times a day for 10 days is safe and does not cause any noticeable toxic effect in healthy volunteers.

Dilemmas in chronic/persistent pain management

The burden of chronic/persistent pain is substantial for the patient and society as a whole. Although a variety of pharmacologic treatments are available, chronic/persistent pain remains inadequately treated. Many pharmacologic treatment options provide analgesic efficacy for 4 to 6 hours, requiring multiple doses for continuous pain relief. The inconvenience of multiple doses may prevent many patients from achieving adequate pain relief. Other limitations to the current pharmacologic treatment options include gastrointestinal effects, cardiovascular effects, and organ toxicity, as well as fear of abuse or addiction. The purpose of this review is to highlight the burden of chronic/persistent pain in today's society and discuss the limitations of short-acting pharmacologic therapies used in the treatment of chronic/persistent pain.