Subjective, psychomotor, and analgesic effects of oral codeine and morphine in healthy volunteers

PBPK-PD model for predicting morphine pharmacokinetics, CNS effects and naloxone antagonism in humans

Morphine and morphine-6-glucuronide (M6G) produce central nervous system (CNS) effects by activating mu-opioid receptors, while naloxone is used mainly for the reversal of opioid overdose, specifically for the fatal complication of respiratory depression, but also for alleviating opioid-induced side effects. In this study we developed a physiologically-based pharmacokinetic-pharmacodynamic (PBPK-PD) model to simultaneously predict pharmacokinetics and CNS effects (miosis, respiratory depression and analgesia) of morphine as well as antagonistic effects of naloxone against morphine. The pharmacokinetic and pharmacodynamic parameters were obtained from in vitro data, in silico, or animals. Pharmacokinetic and pharmacodynamic simulations were conducted using 39 and 36 clinical reports, respectively. The pharmacokinetics of morphine and M6G following oral or intravenous administration were simulated, and the PBPK-PD model was validated using clinical observations. The Emax model correlated CNS effects with free concentrations of morphine and M6G in brain parenchyma. The predicted CNS effects were compared with observations. Most clinical observations fell within the 5th-95th percentiles of simulations based on 1000 virtual individuals. Most of the simulated area under the concentration-time curve or peak concentrations also fell within 0.5-2-fold of observations. The contribution of morphine to CNS effects following intravenous or oral administration was larger than that of M6G. Pharmacokinetics and antagonistic effects of naloxone on CNS effects were also successfully predicted using the developed PBPK-PD model. In conclusion, the pharmacokinetics and pharmacodynamics of morphine and M6G, antagonistic effects of naloxone against morphine-induced CNS effects may be successfully predicted using the developed PBPK-PD model based on the parameters derived from in vitro, in silico, or animal studies.

Pharmacological Treatments and Therapeutic Drug Monitoring in Patients with Chronic Pain

Pain is an unpleasant sensory and emotional experience that affects every aspect of a patient's life and which may be treated through different pharmacological and non-pharmacological approaches. Analgesics are the drugs most commonly used to treat pain, and in specific situations, the use of opioids may be considered with caution. These drugs, in fact, do not always induce optimal analgesia in patients, and several problems are associated with their use. The purpose of this narrative review is to describe the pharmacological approaches currently used for the management of chronic pain. We review several aspects, from the pain-scale-based methods currently available to assess the type and intensity of pain, to the most frequently administered drugs (non-narcotic analgesics and narcotic analgesics), whose pharmacological characteristics are briefly reported. Overall, we attempt to provide an overview of different pharmacological treatments while also illustrating the relevant guidelines and indications. We then report the strategies that may be used to reduce problems related to opioid use. Specifically, we focus our attention on therapeutic drug monitoring (TDM), a tool that could help clinicians select the most suitable drug and dose to be used for each patient. The actual potential of using TDM to optimize and personalize opioid-based pain treatments is finally discussed based on recent scientific reports.

Low-dose morphine reduces tolerance to central hypovolemia in healthy adults without affecting muscle sympathetic outflow

Hemorrhage is a leading cause of preventable battlefield and civilian trauma deaths. Low-dose (i.e., an analgesic dose) morphine is recommended for use in the prehospital (i.e., field) setting. Morphine administration reduces hemorrhagic tolerance in rodents. However, it is unknown whether morphine impairs autonomic cardiovascular regulation and consequently reduces hemorrhagic tolerance in humans. Thus, the purpose of this study was to test the hypothesis that low-dose morphine reduces hemorrhagic tolerance in conscious humans. Thirty adults (15 women/15 men; 29 ± 6 yr; 26 ± 4 kg·m-2, means ± SD) completed this randomized, crossover, double-blinded, placebo-controlled trial. One minute after intravenous administration of morphine (5 mg) or placebo (saline), we used a presyncopal limited progressive lower-body negative pressure (LBNP) protocol to determine hemorrhagic tolerance. Hemorrhagic tolerance was quantified as a cumulative stress index (mmHg·min), which was compared between trials using a Wilcoxon matched-pairs signed-rank test. We also compared muscle sympathetic nerve activity (MSNA; microneurography) and beat-to-beat blood pressure (photoplethysmography) during the LBNP test using mixed-effects analyses [time (LBNP stage) × trial]. Median LBNP tolerance was lower during morphine trials (placebo: 692 [473-997] vs. morphine: 385 [251-728] mmHg·min, P < 0.001, CI: -394 to -128). Systolic blood pressure was 8 mmHg lower during moderate central hypovolemia during morphine trials (post hoc P = 0.02; time: P < 0.001, trial: P = 0.13, interaction: P = 0.006). MSNA burst frequency responses were not different between trials (time: P < 0.001, trial: P = 0.80, interaction: P = 0.51). These data demonstrate that low-dose morphine reduces hemorrhagic tolerance in conscious humans. Thus, morphine is not an ideal analgesic for a hemorrhaging individual in the prehospital setting.NEW & NOTEWORTHY In this randomized, crossover, placebo-controlled trial, we found that tolerance to simulated hemorrhage was lower after low-dose morphine administration. Such reductions in hemorrhagic tolerance were observed without differences in MSNA burst frequency responses between morphine and placebo trials. These data, the first to be obtained in conscious humans, demonstrate that low-dose morphine reduces hemorrhagic tolerance. Thus, morphine is not an ideal analgesic for a hemorrhaging individual in the prehospital setting.

Low-Dose Morphine Reduces Pain Perception and Blood Pressure, but Not Muscle Sympathetic Outflow, Responses During the Cold Pressor Test

Our knowledge about how low-dose (analgesic) morphine affects autonomic cardiovascular regulation is primarily limited to animal experiments. Notably, it is unknown if low-dose morphine affects human autonomic cardiovascular responses during painful stimuli in conscious humans. Therefore, we tested the hypothesis that low-dose morphine reduces perceived pain and subsequent sympathetic and cardiovascular responses in humans during an experimental noxious stimulus. Twenty-nine participants (14F/15M; 29±6 y; 26±4 kg•m^-2, mean ± SD) completed this randomized, crossover, placebo-controlled trial during two laboratory visits. During each visit, participants completed a cold pressor test (CPT; hand in ~0.4 °C ice bath for two minutes) before and ~35 minutes after drug/placebo administration (5 mg IV morphine or saline). We compared pain perception (100 mm visual analog scale), muscle sympathetic nerve activity (MSNA; microneurography; 14 paired recordings), and beat-to-beat blood pressure (BP; photoplethysmography) between trials (at both pre- and post-drug/placebo time points) using paired, two-tailed t-tests. Before drug/placebo infusion, perceived pain (p=0.92), Δ MSNA burst frequency (n=14, p=0.21), and Δ mean BP (p=0.39) during the CPT were not different between trials. After the drug/placebo infusion, morphine versus placebo attenuated perceived pain (morphine: 43±20 vs. placebo: 57±24 mm,p<0.001) and Δ mean BP (morphine: 10±7 vs. placebo: 13±8 mmHg,p=0.003), but not Δ MSNA burst frequency (morphine: 10±11 vs. placebo: 13±11 bursts/minute,p=0.12), during the CPT. Reductions in pain perception and Δ mean BP were only weakly related (r=0.34,p=0.07; post-morphine CPT minus post-placebo CPT). These data provide valuable information regarding how low-dose morphine affects autonomic cardiovascular responses during an experimental painful stimulus.

Model-Based Analysis of the Influence of Alcohol Use and Age on Pharmacokinetics-Pharmacodynamics of Oral Oxycodone in Middle-Age and Older Community Dwelling Adults

Little is known on how opioid responses vary by age and in the presence of alcohol consumption. This model-based pharmacokinetic-pharmacodynamic (PK-PD) analysis quantified the impact of age and alcohol use on pupillometry and cold pressor test (CPT) PD based on data from an open label study of immediate-release 10 mg oral oxycodone in middle-age and older adults (age 35-85) without severe functional limitations. PK and pupillometry assessments were obtained on 11 occasions over 8 hours. CPT was administered at 1.5, 5 and 8 hours post oxycodone dosing. The study consisted of 62 older adults (age 60+) and 66 middle-age adults (age 35-59), with 82% meeting the unhealthy drinking criteria. Oral oxycodone PK were well described using a one compartment model with a sequential zero to first order absorption process. Recent alcohol use measures were selected a priori. for the analysis. Inhibitory Emax and linear direct effect PD models described the respective pupillometry and CPT data using simultaneous PK-PD analysis in MONOLIX. This analysis demonstrated an influence of age on clearance and bodyweight on the distribution volume of oxycodone, alcohol consumption was not noted to alter oxycodone PK. Oxycodone pupillometry PD were influenced by the level of subject-reported alcohol consumption (AUDIT-C), alcohol use biomarker blood phosphatidylethanol, previous cannabis use, and age. Over the opioid exposure range of the study, none of the covariables including alcohol and age were noted to affect CPT PD. Additional clinical studies are needed to further probe the clinical consequences of opioid-alcohol-age interaction. This article is protected by copyright. All rights reserved.

Elevated customary alcohol consumption attenuates opioid effects

BACKGROUND

Regular alcohol consumption is on the rise among older adults and has the potential of altering the subjective experience of pain and response to pain medications. This study examined the cognitive, analgesic and side effect response to oxycodone in middle age and older adults with elevated levels of customary alcohol consumption in a human laboratory setting.

METHODS

After refraining from alcohol for one day, eligible participants underwent baseline assessment cognition and side effects by means of questionnaires that were repeated at three time points (90 min, 5 and 8 h) following administration of a 10 mg oral dose of oxycodone. Response to pain stimulus (Cold Pressor Test (CPT)), pupil size, and plasma oxycodone were also measured.

RESULTS

One hundred twenty-eight adults (age 35-85) completed the study day. Compared to those with lower customary alcohol consumption, participants with elevated alcohol consumption showed attenuated opioid-induced pupil constriction and cognitive decline on objective measures of working memory, sustained attention, inhibitory control, coordination on a simulated driving task, and subjective dysphoric effects with enhanced subjective euphoric effects. Oxycodone pharmacokinetics, pain tolerance to CPT, and Berg balance were impacted comparably between alcohol consumption groups. Women endorsed greater negative drug effects, whereas men endorsed positive drug effects.

CONCLUSION

Independent of subject's age, elevated customary alcohol consumption attenuates opioid central effects (i.e., pupil miosis, impaired cognition) and gender influences subjective drug effects. Clinicians should consider alcohol consumption and gender when prescribing opioid medications.

A new minisatellite VNTR marker, Pscp1, discovered for the identification of opium poppy

Opium poppy, a member of the Papaveraceae family, is an ancient herbaceous plant and well-known medical resource in the pharmaceutical industry. However, opium poppies are grown worldwide for producing illicit drugs, significantly increasing the incidence of narcotic drug abuse. Since the narcotic poppy has not yet been genetically investigated, we characterized a novel variable number tandem repeat (VNTR) marker of forensically important poppy species based on the genetic analysis of 164 samples collected from two locations spanning the Jeolla province and Jeju island of South Korea. Comparing analysis of the chloroplast (cp) genome sequences for four representative species of Papaver (Papaver somniferum, Papaver somniferum subs. setigerum, Papaver orientale, and Papaver rhoeas) revealed a unique region with 1-3 repeats for 16 nucleotide motifs in the genome inverted repeat A (IRA, positions 128,651 to 128,698) region. For 16 nucleotide motifs, 3 repeats were found in P. somniferum, and 2 repeats were found in P. somniferum subs. setigerum. Therefore, 10 known and the 133 unknown, seized Papaver species were compared to determine whether the species could be identified via variations in the repeat units. The sizes of a novel VNTR ranged from 181 to 252 bp between the species. Phylogenetic analysis confirmed that a novel VNTR, which we named Pscp1, could clearly distinguish between the narcotic and non-narcotic types of Papaver species based on the patterns of sequence variation. Interestingly, we found that Pscp1 could also distinguish between P. somniferum and P. somniferum subs. setigerum. The regions of eight non-narcotic species displayed similar patterns and also differences were found due to the nucleotide substitution and deletion events. The structural differences of Pscp1 were observed within the two narcotic species or between the narcotic and non-narcotic species, suggesting that these variations may act as a genetic marker. We, therefore, developed a new Pscp1 PCR-capillary electrophoresis (CE) method that can reliably identify the narcotic type of Papaver species. Taken together, our findings suggest that the newly developed Pscp1 can be used as an identification marker of opium poppy, and establish that the Pscp1 genotyping method by PCR-CE is an effective primary screening tool that can also contribute to species discrimination in the field of forensic diagnosis and applications.

Cannabis sativa: Interdisciplinary Strategies and Avenues for Medical and Commercial Progression Outside of CBD and THC

Cannabis sativa (Cannabis) is one of the world’s most well-known, yet maligned plant species. However, significant recent research is starting to unveil the potential of Cannabis to produce secondary compounds that may offer a suite of medical benefits, elevating this unique plant species from its illicit narcotic status into a genuine biopharmaceutical. This review summarises the lengthy history of Cannabis and details the molecular pathways that underpin the production of key secondary metabolites that may confer medical efficacy. We also provide an up-to-date summary of the molecular targets and potential of the relatively unknown minor compounds offered by the Cannabis plant. Furthermore, we detail the recent advances in plant science, as well as synthetic biology, and the pharmacology surrounding Cannabis. Given the relative infancy of Cannabis research, we go on to highlight the parallels to previous research conducted in another medically relevant and versatile plant, Papaver somniferum (opium poppy), as an indicator of the possible future direction of Cannabis plant biology. Overall, this review highlights the future directions of cannabis research outside of the medical biology aspects of its well-characterised constituents and explores additional avenues for the potential improvement of the medical potential of the Cannabis plant.

Opioid Use and Driving Performance

INTRODUCTION

The USA is in an opioid epidemic, with an increased number of individuals taking psychoactive drugs while executing the tasks of everyday life, including operating a motor vehicle. The pharmacology of opioids has been widely studied, but the effects of opioids on psychomotor function, driving performance, and the risk of motor vehicle collision remain less clear. Clinicians are faced with the challenge of controlling patient pain while also reconciling conflicting messages from the literature about how safe it is for their patients taking opioids to engage in potentially dangerous routine tasks.

DISCUSSION

This review assesses the current literature regarding opioids as they relate to neurocognitive function, driving performance, and accident risk. Manuscripts are categorized by study context and subject matter: controlled experimental administration, illicit use, prescription use, retrospective forensic toxicology, and polydrug consumption.

CONCLUSION

Illicit use, initiation of therapy, and opioid use in combination with other psychoactive medications are contexts most clearly associated with impairment of driving-related functions and/or operation of a motor vehicle. Clinicians should counsel patients on the risk of impairment when initiating therapy, when co-prescribing opioids and other psychoactive drugs, or when a patient is suspected of having an opioid use disorder.

The role of the opioid system in decision making and cognitive control: A review

The opioid system regulates affective processing, including pain, pleasure, and reward. Restricting the role of this system to hedonic modulation may be an underestimation, however. Opioid receptors are distributed widely in the human brain, including the more “cognitive” regions in the frontal and parietal lobes. Nonhuman animal research points to opioid modulation of cognitive and decision-making processes. We review emerging evidence on whether acute opioid drug modulation in healthy humans can influence cognitive function, such as how we choose between actions of different values and how we control our behavior in the face of distracting information. Specifically, we review studies employing opioid agonists or antagonists together with experimental paradigms of reward-based decision making, impulsivity, executive functioning, attention, inhibition, and effort. Although this field is still in its infancy, the emerging picture suggests that the mu-opioid system can influence higher-level cognitive function via modulation of valuation, motivation, and control circuits dense in mu-opioid receptors, including orbitofrontal cortex, basal ganglia, amygdalae, anterior cingulate cortex, and prefrontal cortex. The framework that we put forward proposes that opioids influence decision making and cognitive control by increasing the subjective value of reward and reducing aversive arousal. We highlight potential mechanisms that might underlie the effects of mu-opioid signaling on decision making and cognitive control and provide directions for future research.

Intact responses to non-drug rewards in long-term opioid maintenance treatment

Disruption of non-drug reward processing in addiction could stem from long-term drug use, addiction-related psychosocial stress, or a combination of these. It remains unclear whether long-term opioid maintenance treatment (OMT) disrupts reward processing. Here, we measured subjective and objective reward responsiveness in 26 previously heroin-addicted mothers in >7 years stable OMT with minimal psychosocial stress and illicit drug use. The comparison group was 30 healthy age-matched mothers (COMP). Objective reward responsiveness was assessed in a two-alternative forced-choice task with skewed rewards. Results were also compared to performance from an additional 968 healthy volunteers (meta-analytic approach). We further compared subprocesses of reward-based decisions across groups using computational modelling with a Bayesian drift diffusion model of decision making. Self-reported responsiveness to non-drug rewards was high for both groups (means: OMT = 6.59, COMP = 6.67, p = 0.84, BF₁₀ = 0.29), yielding moderate evidence against subjective anhedonia in this OMT group. Importantly, the mothers in OMT also displayed robust reward responsiveness in the behavioral task (t₁₉ = 2.72, p = 0.013, BF₁₀ = 3.98; d = 0.61). Monetary reward changed their task behavior to the same extent as the local comparison group (reward bias OMT = 0.12, COMP = 0.12, p = 0.96, BF₁₀ = 0.18) and in line with data from 968 healthy controls previously tested. Computational modelling revealed that long-term OMT did not even change decision subprocesses underpinning reward behavior. We conclude that reduced sensitivity to rewards and anhedonia are not necessary consequences of prolonged opioid use.

Readiness and recovery: Transferring between methadone and buprenorphine/naloxone for the treatment of opioid use disorder

Long-acting opioids are prescribed as part of treatment for opioid use disorders; methadone and buprenorphine are well researched and commonly prescribed for the treatment of opioid use disorder. Meta-analysis suggests that buprenorphine has a slightly poorer retention rate in treatment as compared to methadone. Benefits of buprenorphine/naloxone include greater ease in ceasing treatment and less use of illicit opioids while in treatment as compared to methadone. There are a number of qualitative and mixed-method studies that ask patients about their experiences of methadone maintenance and buprenorphine maintenance treatment. This research aimed to understand perspectives of receiving buprenorphine/naloxone for the treatment of opioid use disorder. A qualitative descriptive approach was used. Seven participants with a current diagnosis of opioid use disorder treated with buprenorphine/naloxone were interviewed. Thematic analysis extracted four themes: drivers for opioid substitution treatment change; readiness for buprenorphine/naloxone substitution treatment; absence of effect from buprenorphine/naloxone; and an increased sense of citizenship on buprenorphine/naloxone. This study identified a number of factors influencing participants' decision-making in transferring between methadone and buprenorphine/naloxone for the treatment of their opioid use disorder. Methadone was preferred by those seeking sedation and wishing to continue using other opioids, and buprenorphine/naloxone was most effective for participants no longer wishing to experience sedation and seeing opioid abstinence as an end point in their recovery. Changing treatment expectations are important to consider when determining medication selection and highlight the importance of quality information when determining the most suitable medication for the treatment of opioid use disorder.

Self-reported cumulative medical opioid exposure and subjective responses on first use of opioids predict analgesic and subjective responses to placebo-controlled opioid administration

BACKGROUND AND OBJECTIVES

To expand the evidence base needed to enable personalized pain medicine, we evaluated whether self-reported cumulative exposure to medical opioids and subjective responses on first opioid use predicted responses to placebo-controlled opioid administration.

METHODS

In study 1, a survey assessing cumulative medical opioid exposure and subjective responses on first opioid use was created (History of Opioid Medical Exposure (HOME)) and psychometric features documented in a general sample of 307 working adults. In study 2, 49 patients with chronic low back pain completed the HOME and subsequently rated back pain intensity and subjective opioid effects four times after receiving saline placebo or intravenous morphine (four incremental doses) in two separate double-blinded laboratory sessions. Placebo-controlled morphine effects were derived for all outcomes.

RESULTS

Two HOME subscales were supported: cumulative opioid exposure and euphoric response, both demonstrating high test-retest reliability (Intraclass Correlation Coefficients > 0.93) and adequate internal consistency (Revelle's Omega Total = 0.73-0.77). In study 2, higher cumulative opioid exposure scores were associated with significantly greater morphine-related reductions in back pain intensity (p=0.02), but not with subjective drug effects. Higher euphoric response subscale scores were associated with significantly lower overall perceived morphine effect (p=0.003), less sedation (p=0.04), greater euphoria (p=0.03) and greater desire to take morphine again (p=0.02).

DISCUSSION

Self-reports of past exposure and responses to medical opioid analgesics may have utility for predicting subsequent analgesic responses and subjective effects. Further research is needed to establish the potential clinical and research utility of the HOME.

TRIAL REGISTRATION NUMBER

NCT02469077.

Clinical pain, abstraction, and self-control: being in pain makes it harder to see the forest for the trees and is associated with lower self-control

OBJECTIVES

Although abstract thinking is a fundamental dimension of human cognition, it has received scant attention in research on pain and cognition. We hypothesized that physical pain impairs abstraction, because when people experience pain at high intensity levels, attention becomes concretely focused on the self in the here and now, where little else matters than finding relief for the pain they are currently experiencing. We also examined the relationship between pain and self-control, predicting that pain would debilitate self-control.

PATIENTS AND METHODS

Abstraction and self-reported self-control were assessed in 109 patients with musculoskeletal pain. The influence of specific pain qualities, such as pain intensity, pain interference with daily activities, pain duration, and pain persistence, was examined. Furthermore, we assessed other factors (e.g., anxiety, depression, and fatigue) that could be assumed to play a role in the pain experience and in cognitive performance.

RESULTS

Higher pain intensity and persistence were associated with less abstract thinking. Furthermore, self-control decreased with greater pain intensity, persistence, and self-reported pain interference with daily activities. Self-reported depressive symptoms mediated the overall relationship between pain and self-control.

CONCLUSION

Abstraction is compromised in patients reporting higher pain intensity and persistence. Different dimensions of pain also predict lower self-control although depression seems to account for the relationship between overall pain and self-control. The current study is the first to report an association between clinical musculoskeletal pain and abstraction. The results suggest that pain patients may suffer from a broader range of cognitive disadvantages than previously believed.

Acute impairing effects of morphine related to driving: A systematic review of experimental studies to define blood morphine concentrations related to impairment in opioid-naïve subjects

OBJECTIVE

The objective of this study was to look for dose- and concentration-effect relationships in experimental studies on single-dose administration of morphine on traffic-relevant behavioral tests by a systematic literature review and possibly to see whether a dose/concentration could be defined below which few or no tests would be affected.

METHODS

Searches for corresponding literature were conducted using MEDLINE, EMBASE, and PsycINFO, throughout March of 2016. The search strategy consisted of words colligated to cognitive and psychomotor functions of relevance to driving, in relation to morphine administration. The tests were arranged in main groups, and tests showing impairment were categorized by doses as well as calculated plasma concentrations.

RESULTS

Fifteen studies were included in the review. Impairment after the administration of a single intravenously dose of morphine was found in some of the tests on reaction time, attention, and visual functions. No impairment was observed in tests on psychomotor skills and en-/decoding. Tests on reaction time appeared to be less sensitive to the morphine administration, whereas tests on visual functions and attention appeared to be the most sensitive to the morphine administration. Single-dose administration of morphine with dosages up to 5 mg appeared to cause very few effects on traffic-relevant performance tasks. At higher dosages, impairment was found on various tasks but with no clear dose-effect relationship. Plasma morphine concentrations less than 50 nmol/L are most probably accompanied by few effects on traffic-relevant performance tasks.

CONCLUSIONS

A plasma morphine concentration of 50 nmol/L (approximately 14.3 ng/mL) could represent an upper level, under which there is little accompanying road traffic risk. A single dose of 5 mg morphine IV and analgetic equivalence doses of fentanyl, hydromorphone, oxycodone, and oxymorphone are presented with the suggestion that few traffic-relevant effects will appear after such doses.

The Abuse Potential of Prescription Opioids in Humans-Closing in on the First Century of Research

While opioids are very effective analgesics for treating acute pain, humans have struggled with opiate addiction for millenia. An opium abuse epidemic in the early 1900's led the US government to develop a systematic research infrastructure and scientific plan to produce new compounds with analgesic properties but without abuse liability. This review describes the techniques that were developed for testing in the human laboratory, including empirically derived outcome measures and required elements for human abuse potential assessment. The evaluation and characterization of semi-synthetic and synthetic opioids, including full mu opioid agonists, partial agonists and mixed agonist-antagonists, are described across several decades of research. Finally, the prescription opioid epidemic beginning in the 1990's in the US led to a resurgence in abuse potential evaluations, and the application of these methods to the study of novel abuse-deterrent formulations is discussed.

Impaired psychomotor ability and attention in patients with persistent pain: a cross-sectional comparative study

Background and aims

Patients with pain have shown cognitive impairment across various domains. Although the pain qualities vary among patients, research has overlooked how cognitive performance is affected by the duration and persistence of pain. The current study sought to fill this gap by examining how qualitatively different pain states relate to the following cognitive functions: sustained attention, cognitive control, and psychomotor ability.

Patients and methods

Patients with musculoskeletal pain in primary care were divided into three pain groups: acute pain (duration <3 months), regularly recurrent pain (duration >3 months), and persistent pain (duration >3 months). These groups were then compared with healthy controls. The MapCog Spectra Test, the Color Word Test, and the Grooved Pegboard Test were used to measure sustained attention, cognitive control, and psychomotor ability, respectively.

Results

Patients with persistent pain showed significantly worse sustained attention and psychomotor ability compared with healthy controls. The acute pain group showed a significant decrease in psychomotor ability, and the regularly recurrent pain group showed a significant decrease in sustained attention. These results remained unchanged when age, education, and medication were taken into account.

Conclusion

Persistent musculoskeletal pain seems to impair performance on a wider range of cognitive tasks than acute or regularly recurrent pain, using pain-free individuals as a benchmark. However, there is some evidence of impairment in psychomotor ability among patients with acute pain and some impairment in sustained attention among patients with regularly recurrent pain.

Implications

Caregivers may need to adjust communication methods when delivering information to cognitively impaired patients.

Pharmacodynamic effects of oral oxymorphone: abuse liability, analgesic profile and direct physiologic effects in humans

Oxymorphone is a semisynthetic μ-opioid agonist, marketed as a prescription analgesic purported to be twice as potent as oxycodone for pain relief. Oral formulations of oxymorphone were reintroduced in the United States in 2006 and reports of abuse ensued; however, there are limited data available on its pharmacodynamic effects. The current study aimed to examine the direct physiologic effects, relative abuse liability, analgesic profile and overall pharmacodynamic potency of oxymorphone in comparison with identical doses of oxycodone. Healthy, non-dependent opioid abusers (n = 9) were enrolled in this within-subject, double-blind, placebo-controlled, 3-week inpatient study. Seven experimental sessions (6.5 hours) were conducted, during which an oral dose of immediate-release formulations of oxymorphone (10, 20 and 40 mg), oxycodone (10, 20 and 40 mg) or placebo was administered. An array of physiologic, abuse liability and experimental pain measures was collected. At identical doses, oxymorphone produced approximately twofold less potent effects on miosis, compared with oxycodone. Oxymorphone also produced lesser magnitude effects on measures of respiratory depression, two experimental pain models and observer-rated agonist effects. However, 40 mg of oxymorphone was similar to 40 mg of oxycodone on several abuse-related subjective ratings. Formal relative potency analyses were largely invalid because of the substantially greater effects of oxycodone. Overall, oxymorphone is less potent on most pharmacodynamic measures, although at higher doses, its abuse liability is similar to oxycodone. These data suggest that the published clinical equianalgesic estimates may not be consistent with the observed direct physiologic effects of opioids, results of experimental pain models or abuse liability measures, as assessed in the human laboratory.

Relationship between endogenous opioid function and opioid analgesic adverse effects

BACKGROUND AND OBJECTIVES

Our recent work indicates that endogenous opioid activity influences analgesic responses to opioid medications. This secondary analysis evaluated whether endogenous opioid activity is associated with degree of opioid analgesic adverse effects, and whether chronic pain status and sex affect these adverse effects.

METHODS

Using a double-blind, randomized, placebo-controlled, crossover design, 51 subjects with chronic low back pain and 38 healthy controls participated in 3 separate sessions, undergoing 2 laboratory-evoked pain tasks (ischemic and thermal) after receiving placebo, naloxone, or morphine. Endogenous opioid system function was indexed by the difference in pain responses between the placebo and naloxone conditions. These measures were examined for associations with morphine-related adverse effects.

RESULTS

Chronic pain subjects reported significantly greater itching and unpleasant bodily sensations with morphine than controls (P < 0.05). Across groups, only 6 of 112 possible associations between adverse effects and blockade effects were significant. For the ischemic task, higher endogenous opioid function was associated with greater itching (visual analog scale [VAS]; P < 0.05), numbness (tolerance; P < 0.001), dry mouth (tolerance; P < 0.05), and unpleasant bodily sensations (VAS; P < 0.05). For the thermal task, higher endogenous opioid function was associated with greater numbness (VAS; P < 0.05) and feeling carefree (VAS; P < 0.05). There were no significant main or interaction effects of chronic pain status or sex on these findings.

CONCLUSIONS

No consistent relationships were observed between endogenous opioid function and morphine-related adverse effects. This is in stark contrast to our previous observation of strong relationships between elevated endogenous opioid function and smaller morphine analgesic effects.

Effects of oxycodone on brain responses to emotional images

RATIONALE

Evidence from animal and human studies suggests that opiate drugs decrease emotional responses to negative stimuli and increase responses to positive stimuli. Such emotional effects may motivate misuse of oxycodone (OXY), a widely abused opiate. Yet, we know little about how OXY affects neural circuits underlying emotional processing in humans.

OBJECTIVE

We examined effects of OXY on brain activity during presentation of positive and negative visual emotional stimuli. We predicted that OXY would decrease amygdala activity to negative stimuli and increase ventral striatum (VS) activity to positive stimuli. Secondarily, we examined the effects of OXY on other emotional network regions on an exploratory basis.

METHODS

In a three-session study, healthy adults (N = 17) received placebo, 10 and 20 mg OXY under counterbalanced, double-blind conditions. At each session, participants completed subjective and cardiovascular measures and underwent functional MRI (fMRI) scanning while completing two emotional response tasks.

RESULTS

Our emotional tasks reliably activated emotional network areas. OXY produced subjective effects but did not alter either behavioral responses to emotional stimuli or activity in our primary areas of interest. OXY did decrease right medial orbitofrontal cortex (MOFC) responses to happy faces.

CONCLUSIONS

Contrary to our expectations, OXY did not affect behavioral or neural responses to emotional stimuli in our primary areas of interest. Further, the effects of OXY in the MOFC would be more consistent with a decrease in value for happy faces. This may indicate that healthy adults do not receive emotional benefits from opiates, or the pharmacological actions of OXY differ from other opiates.

Effects of three therapeutic doses of codeine/paracetamol on driving performance, a psychomotor vigilance test, and subjective feelings

RATIONALE

Some recent pharmacoepidemiological studies revealed an elevated risk of driving accidents after opioid analgesics uses. Among analgesics, codeine is often associated with paracetamol in numerous pharmaceutical specialties.

OBJECTIVES

The objective of this study was to evaluate the dose-effect relationship of three usual therapeutic doses of codeine/paracetamol on driving ability, psychomotor performance, subjective alertness, in link with blood concentrations in healthy young volunteers.

METHODS

Driving performance, responses to psychomotor vigilance tests, and scales reflecting alertness were evaluated during the morning after drug intake in a double-blind, randomized, placebo-controlled study. Sixteen healthy volunteers (23.4 ± 2.7 years old, 8 men and 8 women) participated in this balanced, cross-over study. Three doses of codeine/paracetamol (20/400, 40/800, 60/1200 mg) were evaluated against placebo. Two blood samples were collected, 1 and 4 h after drug intake. In serum, codeine and morphine concentrations were determined in serum using high-performance liquid chromatography electrospray ionization-tandem mass spectrometry, and paracetamol concentrations using fluorescence polarization immunoassay.

RESULTS

Driving and psychomotor performance were not affected by any of the three codeine/paracetamol doses. However, significant, though modest, correlations were observed between the driving parameters and both morphine and codeine blood concentrations.

CONCLUSIONS

This study did not reveal any significant impairment in performance due to the three therapeutic doses used in healthy young volunteers. However, the relationships between drug blood concentration and behavioral measures suggest that an inter-subject variability in blood concentration may influence the power of the observed drug effect.

Abuse liability and reinforcing efficacy of oral tramadol in humans

BACKGROUND

Tramadol, a monoaminergic reuptake inhibitor, is hepatically metabolized to an opioid agonist (M1). This atypical analgesic is generally considered to have limited abuse liability. Recent reports of its abuse have increased in the U.S., leading to more stringent regulation in some states, but not nationally. The purpose of this study was to examine the relative abuse liability and reinforcing efficacy of tramadol in comparison to a high (oxycodone) and low efficacy (codeine) opioid agonist.

METHODS

Nine healthy, non-dependent prescription opioid abusers (6 male and 3 female) participated in this within-subject, randomized, double blind, placebo-controlled study. Participants completed 14 paired sessions (7 sample and 7 self-administration). During each sample session, an oral dose of tramadol (200 and 400 mg), oxycodone (20 and 40 mg), codeine (100 and 200 mg) or placebo was administered, and a full array of abuse liability measures was collected. During self-administration sessions, volunteers were given the opportunity to work (via progressive ratio) for the sample dose or money.

RESULTS

All active doses were self-administered; placebo engendered no responding. The high doses of tramadol and oxycodone were readily self-administered (70%, 59% of available drug, respectively); lower doses and both codeine doses maintained intermediate levels of drug taking. All three drugs dose-dependently increased measures indicative of abuse liability, relative to placebo; however, the magnitude and time course of these and other pharmacodynamic effects varied qualitatively across drugs.

CONCLUSIONS

This study demonstrates that, like other mu opioids, higher doses of tramadol function as reinforcers in opioid abusers, providing new empirical data for regulatory evaluation.

Can patients receiving opioid maintenance therapy safely drive? A systematic review of epidemiological and experimental studies on driving ability with a focus on concomitant methadone or buprenorphine administration

OBJECTIVE

To perform a systematic review of the present scientific literature on the treatment with methadone or buprenorphine related to (1) traffic accident risk in epidemiological studies and (2) their effects on cognitive and psychomotor functions of relevance to driving in experimental studies.

METHODS

Searches for corresponding literature were conducted in MEDLINE, EMBASE, and PsycINFO throughout March and June of 2010. The search strategy consisted of words colligated to accident risk and culpability, in addition to cognitive and psychomotor functions of relevance to driving, all in relation to methadone or buprenorphine administration. In total, 59 studies were included.

RESULTS

Early epidemiological studies found no substantial difference in motor vehicle accident risk between methadone maintenance therapy patients (MMPs) and control groups. However, more recent studies have found an increased risk of traffic accident involvement for both MMPs and buprenorphine maintenance therapy patients (BMPs). In experimental studies, impairments of cognitive and psychomotor functions have been observed among both MMPs and BMPs when compared to control groups. When comparing MMPs with BMPs, the latter appeared to be less impaired than MMPs, but this difference may be unrelated to the maintenance therapy. Further impairments have been observed among MMPs after single doses, after an additional versus regular daily dosing, in multiple versus single dosing, and after long-term treatment compared to baseline levels. All studies showed impairments among opioid-naïve subjects after the administration of a comparatively low and single dose of either methadone or buprenorphine.

CONCLUSIONS

Both methadone and buprenorphine were confirmed as having impairing potentials in opioid-naïve subjects. At least some opioid maintenance therapy patients are observed having only slight impairments of relevance to driving. Knowing this when approaching the question of ability to drive, an individual evaluation of the driving performance, pertaining to the opioid maintained patient, may be the most useful and conclusive procedure.

Human experimental pain models for assessing the therapeutic efficacy of analgesic drugs

Pain models in animals have shown low predictivity for analgesic efficacy in humans, and clinical studies are often very confounded, blurring the evaluation. Human experimental pain models may therefore help to evaluate mechanisms and effect of analgesics and bridge findings from basic studies to the clinic. The present review outlines the concept and limitations of human experimental pain models and addresses analgesic efficacy in healthy volunteers and patients. Experimental models to evoke pain and hyperalgesia are available for most tissues. In healthy volunteers, the effect of acetaminophen is difficult to detect unless neurophysiological methods are used, whereas the effect of nonsteroidal anti-inflammatory drugs could be detected in most models. Anticonvulsants and antidepressants are sensitive in several models, particularly in models inducing hyperalgesia. For opioids, tonic pain with high intensity is attenuated more than short-lasting pain and nonpainful sensations. Fewer studies were performed in patients. In general, the sensitivity to analgesics is better in patients than in healthy volunteers, but the lower number of studies may bias the results. Experimental models have variable reliability, and validity shall be interpreted with caution. Models including deep, tonic pain and hyperalgesia are better to predict the effects of analgesics. Assessment with neurophysiologic methods and imaging is valuable as a supplement to psychophysical methods and can increase sensitivity. The models need to be designed with careful consideration of pharmacological mechanisms and pharmacokinetics of analgesics. Knowledge obtained from this review can help design experimental pain studies for new compounds entering phase I and II clinical trials.

The impact of long-term maintenance treatment with buprenorphine on complex psychomotor and cognitive function

INTRODUCTION

Despite the fact that buprenorphine is effective, well tolerated and due to its pharmacological profile a very safe drug, the impact of long-term buprenorphine substitution therapy on complex psychomotor and cognitive function predicting driving ability is not yet clear. Therefore, a prospective comparison between patients receiving sublingual buprenorphine and a control group of untreated, healthy volunteers was performed.

METHODS

Treated and untreated subjects were matched for age and sex, with three control subjects selected for every buprenorphine patient. Patients using unreported drugs were included in the intention-to-treat (ITT) analysis; the remaining patients were analysed as the per-protocol (PP) group. The test battery comprised the assessment of: performance during stress, visual orientation, concentration, attention, vigilance and reaction time. The primary endpoint was defined as the sum of the relevant scores of the tests after z-transformation of the individual scores.

RESULTS

30 patients with sublingual buprenorphine treatment (7.7±3.9 mg per day) were matched to 90 controls. 19 patients were excluded from the PP-analysis because of additional unreported drug intake. Significant non-inferiority could be demonstrated for the PP-group (p<0.05) as well as for the ITT-group (p<0.001).

CONCLUSION

Patients receiving a stable dose of sublingual buprenorphine showed no significant impairment of complex psychomotor or cognitive performance as compared to healthy controls. However intake of illicit drugs as well as the lack of social reliability are major problems in this specific patients group. Despite of the absence of a relevant impact of the drug on driving ability, those patients do not seem to be qualified for getting their driving license.

Evaluation of potential sex differences in the subjective and analgesic effects of morphine in normal, healthy volunteers

RATIONALE

Sex differences in the analgesic effects of mu-opioid agonists have been documented extensively in rodents and, to a lesser extent, in non-human primates. To date, there have been few experimental studies investigating this effect in humans, and the conclusions have been equivocal.

OBJECTIVES

The aims of the present study were to examine potential sex differences in the analgesic, subjective, performance, and physiological effects of morphine in human research volunteers.

METHODS

Using a double-blind outpatient procedure, the present study investigated the effects of intramuscular morphine (0, 5, and 10 mg/70 kg, i.m.) in men (N = 8) and women (N = 10). The primary dependent measure was analgesia, as assessed by the cold pressor and mechanical pressure tests. Secondary dependent measures included subjective, performance, and physiological effects of morphine, as well as plasma levels of morphine.

RESULTS

No differences in the analgesic and performance effects of morphine were observed between men and women, but significant differences in morphine's subjective effects were found. Specifically, men reported greater positive effects, whereas women reported greater negative effects after morphine administration.

CONCLUSIONS

These data suggest that, in humans, there are sex differences in the subjective mood-altering effects of morphine but, based on this limited sample, there is little evidence for sex differences in its analgesic effects.

Comparative cognitive and subjective side effects of immediate-release oxycodone in healthy middle-aged and older adults

This study measured the objective and subjective neurocognitive effects of a single 10-mg dose of immediate-release oxycodone in healthy, older (> 65 years), and middle-aged (35 to 55 years) adults who were not suffering from chronic or significant daily pain. Seventy-one participants completed 2 separate study days and were blind to medication condition (placebo, 10-mg oxycodone). Plasma oxycodone concentration peaked between 60 and 90 minutes postdose (P < .01) and pupil size, an indication of physiological effects of the medication, peaked at approximately 90 to 120 minutes postdose (P < .01). Significant declines in simple and sustained attention, working memory, and verbal memory were observed at 1 hour postdose compared to baseline for both age groups with a trend toward return to baseline by 5 hours postdose. For almost all cognitive measures, there were no medication by age-interaction effects, which indicates that the 2 age groups exhibited similar responses to the medication challenge. This study suggests that for healthy older adults who are not suffering from chronic pain, neurocognitive and pharmacodynamic changes in response to a 10-mg dose of immediate-release oxycodone are similar to those observed for middle-aged adults.

PERSPECTIVE

Study findings indicate that the metabolism, neurocognitive effects, and physical side effects of oral oxycodone are similar for healthy middle-aged and older adults. Therefore, clinicians should not avoid prescribing oral opioids to older adults based on the belief that older adults are at higher risk for side effects than younger adults.

Randomized double-blind placebo controlled crossover study of acetaminophen, ibuprofen, acetaminophen/hydrocodone, and placebo for the relief of pain from a standard painful stimulus

OBJECTIVES

The objective was to compare subjects' change in perceived acute pain from an identical painful stimulus after receiving three separate, commonly used pain medications and placebo.

METHODS

This was an institutional review board-approved, randomized, double-blind crossover study of healthy human volunteers. Subjects received 1000 mg of acetaminophen, 800 mg of ibuprofen, the combination of 650 mg of acetaminophen with 10 mg of hydrocodone, or placebo (800 mg of lactose) in a randomized order over four separate occasions each 1 week apart. Prior to receiving the drug on each study day, subjects placed their nondominant hand in a bath of 0 degrees C water for 45 seconds. The bath was divided into two sections; the larger was the reservoir of cooled water monitored at 0 degrees C, and the other half was filled from constant overflow. Water drained from the overflow section into the cooling unit and was then pumped up into the base of the reservoir through a diffusion grid. Subjects completed a 100-mm visual analog scale (VAS) representing perceived pain during the exposure. The cold water exposure and VAS were repeated 1 hour after receiving the study drug, and then subjects were observed for side effects for 4 hours. Data were compared using descriptive statistics, 95% confidence intervals (CIs), and repeated-measures analysis of variance (ANOVA).

RESULTS

Twenty-five subjects were enrolled. The mean VAS preexposure was 56.9 mm (+/-15.1 mm; range = 5 to 92 mm). The mean decrease in VAS after receiving the study drug for acetaminophen was 10.2% (95% CI = -1.4 to 20.4), for ibuprofen was -6.6% (95% CI = -16.5 to 3.20), for acetaminophen/hydrocodone was 9.5% (95% CI = 1.4 to 20.4), and for placebo was -6.9% (95% CI = -15.2 to 1.4). The range in change in pain scores for all agents was -91.3% to 57.6%. Mild side effects (nausea, dizziness, or somnolence) were reported in 11 subjects (44%) after receiving acetaminophen/hydrocodone; no other side effects were reported.

CONCLUSIONS

There was a wide range of changes in pain scores from this identical painful stimulus after receiving the study medications. Acetaminophen and acetaminophen/hydrocodone resulted in a similar decrease in pain (10.2 and 9.5%), while ibuprofen and placebo had a similar lack of effect (-6.6 and -6.9%). Forty-four percent of subjects receiving acetaminophen/hydrocodone reported mild side effects; no other side effects were seen. In this noninflammatory pain model, the VAS is not able to distinguish differences in pain relief between acetaminophen and acetaminophen/hydrocodone or ibuprofen and placebo.

Assessing analgesic actions of opioids by experimental pain models in healthy volunteers - an updated review

AIM

Experimental pain models may help to evaluate the mechanisms of action of analgesics and target the clinical indications for their use. This review addresses how the efficacy of opioids can be assessed in human volunteers using experimental pain models. The drawback with the different study designs is also discussed.

METHOD

A literature search was completed for randomized controlled studies which included human experimental pain models, healthy volunteers and opioids.

RESULTS

Opioids with a strong affinity for the micro-opioid receptor decreased the sensation in a variety of experimental pain modalities, but strong tonic pain was attenuated more than short lasting pain and non-painful sensations. The effects of opioids with weaker affinity for the micro-opioid receptor were detected by a more narrow range of pain models, and the assessment methods needed to be more sensitive.

CONCLUSION

The way the pain is induced, assessed and summarized is very important for the sensitivity of the pain models. This review gives an overview of how different opioids perform in experimental pain models. Generally experimental pain models need to be designed with careful consideration of pharmacological mechanisms and pharmacokinetics of analgesics. This knowledge can aid the decisions needed to be taken when designing experimental pain studies for compounds entering phase 1 clinical trials.

Sensorimotor gating and attentional set-shifting are improved by the mu-opioid receptor agonist morphine in healthy human volunteers

Prepulse inhibition (PPI) of the acoustic startle response (ASR) has been established as an operational measure of sensorimotor gating. Animal and human studies have shown that PPI can be modulated by dopaminergic, serotonergic, and glutamatergic drugs and consequently it was proposed that impaired sensorimotor gating in schizophrenia parallels a central abnormality within the corresponding neurotransmitter systems. Recent animal studies suggest that the opioid system may also play a role in the modulation of sensorimotor gating. Thus, the present study investigated the influence of the mu-opioid receptor agonist morphine on PPI in healthy human volunteers. Eighteen male, non-smoking healthy volunteers each received placebo or 10 mg morphine sulphate (p.o.) at a 2-wk interval in a double-blind, randomized, and counterbalanced order. PPI was measured 75 min after drug/placebo intake. The effects of morphine on mood were measured by the Adjective Mood Rating Scale and side-effects were assessed by the List of Complaints. Additionally, we administered a comprehensive neuropsychological test battery consisting of tests of the Cambridge Neuropsychological Test Automated Battery and the Rey Auditory Verbal Learning Test. Morphine significantly increased PPI without affecting startle reactivity or habituation. Furthermore, morphine selectively improved the error rate in an attentional set-shifting task but did not influence vigilance, memory, or executive functions. These results imply that the opioid system is involved in the modulation of PPI and attentional set-shifting in humans and they raise the question whether the opioid system plays a crucial role also in the regulation of PPI and attentional set-shifting in schizophrenia.

Assessing cognition and psychomotor function under long-term treatment with controlled release oxycodone in non-cancer pain patients

BACKGROUND

The therapeutic use of opioids can be associated with altered cognition and impaired psychomotor function. Several studies have demonstrated the impact of opioid therapy on psychomotor performance and cognition, but no data exist about the effect of long-term treatment with controlled release oxycodone (CRO) on driving ability.

METHODS

Thirty patients suffering from chronic non-cancer pain who had been treated with stable doses of CRO where included in a prospective trial and compared with 90 healthy volunteers (matched pairs). A computerized test battery that was developed to assess the driving ability of traffic delinquents in Germany was employed. Attention reaction, visual orientation, motor coordination and vigilance were evaluated. The data from a total of 11 parameters were assessed and for each test a relevant score was defined. As the primary endpoint the sum score of the three relevant scores was determined. A weaker statistical means to assess the patients' performance is to compare the test results with an age-independent control group. Individuals performing worse than the 16th percentile of this control group are considered to be unable to drive according to German legislation.

RESULTS

Significant non-inferiority could not be demonstrated for the primary endpoint. However, driving ability as defined as a result above the 16th percentile did not differ significantly between the patients receiving CRO and the age-independent control group.

CONCLUSION

The use of CRO does not prohibit driving, but individual assessment is necessary.

The effects of tramadol on static and dynamic pupillometry in healthy subjects--the relationship between pharmacodynamics, pharmacokinetics and CYP2D6 metaboliser status

OBJECTIVES

The main objective of the present study was to provide information on whether static and dynamic pupillometry can be used for pharmacodynamic profiling, particularly when investigating opioid-like drugs, such as tramadol.

METHODS

Healthy subjects (n = 26) participated in this randomised, double-blind, placebo-controlled, crossover Phase 1 study. Of these, 20 extensive metabolisers (EMs) with respect to polymorphic isoenzyme cytochrome P450 2D6 (CYP2D6) received up to 150 mg of tramadol-HCl and placebo. The 6 poor metabolisers (PMs) with respect to CYP2D6 received 100 mg tramadol-HCl and placebo.

RESULTS

In EMs, serum concentrations of the enantiomers of tramadol and of O-demethylated metabolite (M1) increased with increasing doses. Comparing the 100-mg dose between EMs and PMs, the latter exhibited higher serum concentrations of both enantiomers of tramadol. Serum concentrations of (+)-M1 remained below the lower limit of quantification, and that of (-)-M1 were lower than those in EMs. In EMs, doses from 100 mg tramadol-HCl on induced a significant (P<0.05) miosis as compared with placebo. The maximum mean differences from placebo after dosing with 50, 100 and 150 mg tramadol-HCL were -0.5, -0.8 and -1.1 mm, respectively, indicating a dose-dependent character of the changes. Dynamic pupillometry revealed significant (P<0.05) effects for the amplitude, latency and duration of reaction. The amplitude and velocity of constriction were decreased only at the highest dose; whereas, the changes of the amplitude reached statistical significance (P<0.05). Both the latency and reaction duration behaved in a dose-dependent manner. For the latency, significant changes compared with placebo (P<0.05) were found at the 150-mg dose level, while the reaction duration was already significantly (P<0.05) decreased from the 100-mg dose on. The velocity of redilatation did not respond at all. In PMs, no effect on the initial pupil diameter was found. Although the statistical analysis failed to demonstrate any significant change from placebo for the dynamic pupillometry, the effect-time profiles of EMs and PMs were comparable. For both metaboliser groups, a decrease of amplitude, velocity of constriction and reaction duration as well as an increase of latency was observed. In principle, the direction and magnitude of changes were comparable between EMs and PMs. Most important was the finding that the time course of effects was completely different between both groups of metabolisers. In EMs, effects slowly reached a maximum between 4 h and 10 h after dosing and diminished until 24 h; whereas, in PMs, both maximum effects and the return to baseline occurred much earlier, at approximately 3 h and 8 h, respectively.

CONCLUSIONS

The EMs and PMs of CYP2D6 treated with tramadol behaved differently in static and dynamic pupillometry. The reason for this could largely be explained with the aid of the metaboliser status and the pharmacokinetic properties of tramadol. In EMs, the pupillometric response was mainly driven by the (+)-M1, which comprises the mu action component of tramadol; whereas, in PMs, the non-mu component appears to play an important role. Thus, pupillometry was found to be useful in pharmacodynamic profiling and provides a good correlation with the pharmacokinetics.

A review of drug use and driving: epidemiology, impairment, risk factors and risk perceptions

The existing literature on the prevalence of drug driving, the effects of drugs on driving performance, risk factors and risk perceptions associated with drug driving was reviewed. The 12-month prevalence of drug driving among the general population is approximately 4%. Drugs are detected commonly among those involved in motor vehicle accidents, with studies reporting up to 25% of accident-involved drivers positive for drugs. Cannabis is generally the most common drug detected in accident-involved drivers, followed by benzodiazepines, cocaine, amphetamines and opioids. Polydrug use is common among accident-involved drivers. Studies of impairment indicate an undeniable association between alcohol and driving impairment. There is also evidence that cannabis and benzodiazepines increase accident risk. The most equivocal evidence surrounds opioids and stimulants. It is apparent that drugs in combination with alcohol, and multiple drugs, present an even greater risk. Demographically, young males are over-represented among drug drivers. Although there is an association between alcohol use problems and drink driving, it is unclear whether such an association exists between drug use problems and drug driving. Evidence surrounding psychosocial factors and driving behaviour is also equivocal at this stage. While most drivers perceive drug driving to be dangerous and unacceptable, there is less concern about impaired driving among drug drivers and drink drivers than from those who have not engaged in impaired driving. Risk perceptions differ according to drug type, with certain drugs (e.g. cannabis) seen as producing less impairment than others (e.g. alcohol). It is concluded that drug driving is a significant problem, both in terms of a general public health issue and as a specific concern for drug users.

The cognitive effects of opioids

Successful opioid therapy often depends on achieving a balance between analgesic effectiveness and side effects. The risk of opioid-induced cognitive impairment often hinders clinicians and patients from initiating or optimizing opioid therapy. Despite subjective experiences of mental dullness and sedation, objective tests of cognitive functioning do not always demonstrate marked changes following opioid administration. To guide clinical practice, as well as patient and family teaching, pain management nurses should be familiar with literature regarding this topic. The purpose of this article is to review the empiric literature on opioids and cognitive functioning, including the relationships among pain, cognition, delirium, and opioids. In general, research reflects minimal to no significant impairments in cognitive functioning. If impairment does occur, it is most often associated with parenteral opioids administered to opioid-naive individuals. Some evidence suggests that opioids may actually enhance cognitive function and decrease delirium in some patient populations. This article describes this research and explores the clinical implications of the research in this area.

Effect of oral ketorolac and gender on human cold pressor pain tolerance

1. Although the analgesic effect of opioids on experimental cold pressor (CP) pain has been well demonstrated, the analgesic effect of non-steroidal anti-inflammatory drugs (NSAIDs) on experimental CP pain has been less reliable, a finding complicated by inconsistencies in how CP analgesic effect is measured. 2. In the present study, a clinically relevant CP response of pain tolerance was used to assess the previously undescribed analgesic efficacy of the potent NSAID ketorolac (10 mg, p.o.), on CP pain across gender in a sample of normal subjects (n = 50). 3. Using a placebo-controlled crossover design, neither a main nor interaction effect for ketorolac on CP pain tolerance was detected. When examined by gender, male subjects exhibited a large placebo response to CP pain under study conditions, whereas women (albeit less pain tolerant at baseline) evidenced no placebo effect but a modest-to-good NSAID analgesic response. 4. Findings on the gender-specific placebo and analgesic NSAID response, integrated with the current literature, indicate that the lack of NSAID analgesic efficacy in the CP pain model may be related to unexamined and differential effects of how gender affects NSAID analgesic effect.

Characterizing the subjective, psychomotor, and physiological effects of oral propoxyphene in non-drug-abusing volunteers

BACKGROUND

The subjective, psychomotor, and physiological effects of a widely prescribed prescription opioid, propoxyphene, have not been studied in a population of non-drug-abusing people. The drug also has potential for abuse and it was of interest in the present study to determine if the drug had any abuse liability-related subjective effects in this population.

METHODS

Eighteen volunteers participated in a crossover, randomized, double-blind study in which they received, all p.o., placebo; 50 mg propoxyphene napsylate; 100 mg propoxyphene napsylate; 200 mg propoxyphene napsylate; 40 mg morphine sulfate; and 2 mg lorazepam. Measures were assessed before and for 300 min after drug administration.

RESULTS

Both morphine and lorazepam produced subjective effects. There were no statistically significant subjective effects obtained with any dose of propoxyphene in the group as a whole, but approximately 30-50% of the subjects did appear to experience subjective effects from the drug. Drug liking was not consistently observed in this subset. Propoxyphene, unlike lorazepam, did not impair psychomotor or cognitive performance. Both propoxyphene and morphine produced miosis.

CONCLUSIONS

There was a lack of statistically significant subjective effects of propoxyphene in the group as a whole, including a propoxyphene dose that was twice as high as the typical clinically-prescribed dose of 100 mg. However, there were some subjects who did report effects, consistent with the notion that patients differ in their sensitivity to opioid effects.

Antitussive activity of sigma-1 receptor agonists in the guinea-pig

1. Current antitussive medications have limited efficacy and often contain the opiate-like agent dextromethorphan (DEX). The mechanism whereby DEX inhibits cough is ill defined. DEX displays affinity at both NMDA and sigma receptors, suggesting that the antitussive activity may involve central or peripheral activity at either of these receptors. This study examined and compared the antitussive activity of DEX and various putative sigma receptor agonists in the guinea-pig citric-acid cough model. 2. Intraperitoneal (i.p.) administration of DEX (30 mg kg(-1)) and the sigma-1 agonists SKF-10,047 (1-5 mg kg(-1)), Pre-084 (5 mg kg(-1)), and carbetapentane (1-5 mg kg(-1)) inhibited citric-acid-induced cough in guinea-pigs. Intraperitoneal administration of a sigma-1 antagonist, BD 1047 (1-5 mg kg(-1)), reversed the inhibition of cough elicited by SKF-10,047. In addition, two structurally dissimilar sigma agonists SKF-10,047 (1 mg ml(-1)) and Pre-084 (1 mg ml(-1)) inhibited cough when administered by aerosol. 3. Aerosolized BD 1047 (1 mg ml(-1), 30 min) prevented the antitussive action of SKF-10,047 (5 mg kg(-1)) or DEX (30 mg kg(-1)) given by i.p. administration and, likewise, i.p. administration of BD 1047 (5 mg kg(-1)) prevented the antitussive action of SKF-10,047 given by aerosol (1 mg ml(-1)). 4. These results therefore support the argument that antitussive effects of DEX may be mediated via sigma receptors, since both systemic and aerosol administration of sigma-1 receptor agonists inhibit citric-acid-induced cough in guinea-pigs. While significant systemic exposure is possible with aerosol administration, the very low doses administered (estimated <0.3 mg kg(-1)) suggest that there may be a peripheral component to the antitussive effect.

Long term effects of oral sustained release morphine on neuropsychological performance in patients with chronic non-cancer pain

Morphine is increasingly used in patients with chronic non-cancer pain, but a major concern associated with chronic use relates to possible cognitive side-effects. The aim of this long-term prospective study was to evaluate the cognitive impact of oral sustained release morphine in patients with non-cancer pain. A battery of neuropsychological tests to explore attention, psychomotor speed and memory was administered. The effects of morphine on pain, quality of life, mood, subjective memory impairment and side-effects were also investigated. Evaluations were performed at baseline in patients free from opioids and then after 3, 6 and 12 months. Twenty-eight patients were included: 18 received oral sustained morphine (range 40-140 mg/day), ten patients stopped morphine prematurely because of side-effects or insufficient pain relief and were followed as a control group. There was no impairment of any neuropsychological variable over time in the morphine treated patients in comparison with the control group. Two measures of information processing speed - the Stroop interference score and the digit symbol test were improved at 6 and 12 months and there were significant correlations with the pain relief and improvement of mood. Self-reported memory impairment improved notably in responders to morphine. Morphine induced persisting effects on pain, and to a lesser extent on quality of life and mood. The visual analog scale score for side-effects increased at 12 months and essentially consisted of gastrointestinal disorders. This study demonstrates that 12 months treatment with oral morphine does not disrupt cognitive functioning in patients with chronic non-cancer pain and instead results in moderate improvement of some aspects of cognitive functioning, as a consequence of the pain relief and concomitant improvement of well-being and mood.

Acute psychotropic effects of bilateral subthalamic nucleus stimulation and levodopa in Parkinson's disease

High-frequency deep brain stimulation (DBS) of the subthalamic nucleus (STN) improves the motor symptoms of Parkinson's disease (PD). Opposite changes in mood, such as mania or depression, have been reported after surgery, but it is not known whether these side effects are specifically related to STN DBS. To learn whether STN DBS also influences the limbic loop, we investigated acute subjective psychotropic effects related to levodopa or bilateral STN DBS. After a median postoperative follow-up of 12 months, 50 PD patients completed the Addiction Research Center Inventory (ARCI), assessing subjective psychotropic effects in four conditions: off-drug/on-stimulation; off-drug/off-stimulation; on-drug/off-stimulation; and on-drug/on-stimulation. Both levodopa and STN DBS improved all the ARCI subscales, indicating subjective feelings of well being, euphoria, increase in motivation, and decrease in fatigue, anxiety, and tension. A suprathreshold dose of levodopa was significantly more effective than STN DBS, using the same electrical parameters as for chronic stimulation, on four of the five ARCI subscales. We concluded that 1) both STN DBS and levodopa have synergistic acute beneficial psychotropic effects in PD, 2) the psychotropic effects of both treatments need to be considered in the long-term management of chronic STN DBS, and 3) the results indicate an involvement of the limbic STN in mood disorders of PD.