Subjective, behavioral and physiological responses to intravenous meperidine in healthy volunteers

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.

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.

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.

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

RATIONALE

The subjective, psychomotor, and physiological effects of a widely prescribed and abused prescription opioid, oxycodone, have not been studied in a population of non-drug-abusing people.

OBJECTIVES

To characterize the effects of oxycodone in non-drug-abusing volunteers.

METHODS

Eighteen volunteers participated in a crossover, randomized, double-blind study in which they received, all p.o., placebo, 10 mg oxycodone, 20 mg oxycodone, 30 mg oxycodone, 40 mg morphine, and 2 mg lorazepam. Measures were assessed before and for 300 min after drug administration. End-of-session and 24-h post-session measures were taken to assess residual drug effects and overall subjects' assessments of the drug effects.

RESULTS

Subjective effects of oxycodone were dose related, with the majority of statistically significant effects limited to the two higher doses tested. Oxycodone produced a profile of subjective effects that included both pleasant and unpleasant effects. Morphine in general produced effects similar in magnitude to those of 10 mg and 20 mg oxycodone. Peak liking and drug-wanting ratings were increased by all doses of oxycodone and by morphine, and trough ratings of liking (dislike) were lower in the 20-mg and 30-mg oxycodone conditions, relative to the placebo condition. Post-session ratings of overall liking and drug wanting were not statistically significant, either at the end of the session or 24 h later. Cognitive and psychomotor impairment were obtained with the higher doses of oxycodone, but to a much lesser degree than that of lorazepam. Miosis and exophoria were increased in a dose-related manner by oxycodone.

CONCLUSIONS

Oxycodone produced effects similar to those of other mu opioid agonists. Although oxycodone produced abuse liability-related subjective effects, it also produced unpleasant effects, a phenomenon we have observed in other opioid studies in non-drug-abusing volunteers.

Antagonism of the response rate-decreasing effects of meperidine and morphine by beta-funaltrexamine and naltrexone in squirrel monkeys

Level pressing by squirrel monkeys was maintained under a fixed-ratio 30 schedule of food presentation. The response rate-decreasing effects of meperidine and morphine were examined alone and in combination with several doses of the irreversible, mu-selective opioid antagonist beta-funaltrexamine and the reversible, opioid antagonist naltrexone. beta-Funaltrexamine alone decreased response rates to greater than 50% of control at all doses in two of the four monkeys and at the highest dose in one monkey. In the monkeys in which beta-funaltrexamine decreased rates, beta-funaltrexamine either did not shift the meperidine or the morphine dose-effect curve or it shifted these curves to the left. In the monkeys in which beta-funaltrexamine alone did not decrease rates, it shifted the meperidine and the morphine dose-effect curves to the right. Naltrexone also shifted both the meperidine and morphine dose-effect curves rightward, although not in a dose-dependent manner. These data suggest that the rate-decreasing effects of meperidine and morphine in squirrel monkeys are altered by beta-funaltrexamine and naltrexone in a similar manner, providing additional evidence that the rate-decreasing effects of both meperidine and morphine are mediated by mu-opioid receptors.

The cocaine-like behavioral effects of meperidine are mediated by activity at the dopamine transporter

Meperidine has atypical opioid receptor agonist effects and shares some structural features with the phenyltropane (WIN) analogs of cocaine. In combination with 0.1 mg/kg naltrexone, meperidine produced cocaine-like discriminative stimulus effects in monkeys, whereas morphine was inactive. Both cocaine and meperidine inhibited [3H]dopamine uptake in chopped rat caudate putamen with comparable potencies; meperidine differed from cocaine in that its effects could be characterized as having predominantly a single high-affinity component. Morphine was not active in inhibiting [3H]dopamine uptake, indicating that the effect of meperidine was not via a classic mu-opioid receptor agonist action. Further, meperidine but not morphine displaced [3H]WIN 35,428 (2 beta-carbomethoxy-3 beta-(4-fluorophenyl)tropane) binding. These data suggest that the actions of meperidine that are atypical of opioids are due to activity at the dopamine transporter. In addition, meperidine appears to interact predominantly with the high-affinity component of the dopamine transporter, and this high-affinity component may be the site of importance for the production of cocaine's behavioral effects.

Effects of marijuana history on the subjective, psychomotor, and reinforcing effects of nitrous oxide in humans

An experiment using marijuana users and non-users was conducted to assess whether the reinforcing, subjective, or psychomotor effects of nitrous oxide were influenced by a subject's drug history. Subjects in the first four sessions sampled 40% nitrous oxide in oxygen and 100% oxygen (placebo), and then over the next three sessions, chose which agent they wished to inhale. Choice distributions between the two groups did not differ significantly, and nitrous oxide choice rates were less than 50% in both groups. However, a history of marijuana use appeared to intensify some of the subjective effects induced by nitrous oxide inhalation.

Opioid physical dependence development: effects of single versus repeated morphine pretreatments and of subjects' opioid exposure history

In acute dependence, signs and symptoms of opioid withdrawal are precipitated when an opioid antagonist (naloxone) is administered following acute (e.g. single dose) pretreatment with a mu agonist. This study examined the influence of amount of previous opioid exposure, both immediate and remote, on intensity of precipitated withdrawal effects in an acute dependence model. Two groups of subjects, opioid abusers (n = 20) and nonabusers (n = 20), received either one 15 mg/70 kg IM morphine pretreatment or two such pretreatments spaced 24 h apart. Naloxone challenge (30 mg/70 kg) followed 4.33 h after the second pretreatment. There were clear effects of morphine pretreatment condition (single versus repeated 15 mg) on the intensity of precipitated withdrawal responses elicited by naloxone. More intense effects were seen after the repeated pretreatment, suggesting that physical dependence escalates with repeated opioid exposures spaced at appropriate intervals. Subjects with an opioid abuse history reported greater liking of agonist drug effects than did nonabusers, whereas nonabusers reported more sedating effects. However, an opioid abuse history did not influence the intensity of precipitated withdrawal symptoms and signs. The latter finding suggests that a previous opioid exposure history does not dramatically modulate initial stages of physical dependence development during subsequent opioid exposure episodes.