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

Do initial responses to drugs predict future use or abuse?

Individuals vary in their initial reactions to drugs of abuse in ways that may contribute to the likelihood of subsequent drug use. In humans, most drugs of abuse produce positive subjective states such as euphoria and feelings of well-being, which may facilitate repeated use. In nonhumans, many drugs initially increase locomotor activity and produce discriminative stimulus effects, both of which have been considered to be models of human stimulant and subjective states. Both humans and nonhumans vary in their sensitivity to early acute drug effects in ways that may predict future use or self-administration, and some of these variations appear to be genetic in origin. However, it is not known exactly how the initial responses to drugs in either humans or nonhumans relate to subsequent use or abuse. In humans, positive effects of drugs facilitate continued use of a drug while negative effects discourage use, and in nonhumans, greater genetic risk for drug intake is predicted by reduced sensitivity to drug aversive effects; but whether these initial responses affect escalation of drug use, and the development of dependence is currently unknown. Although early use of a drug is a necessary step in the progression to abuse and dependence, other variables may be of greater importance in the transition from use to abuse. Alternatively, the same variables that predict initial acute drug effects and early use may significantly contribute to continued use, escalation and dependence. Here we review the existing evidence for relations between initial direct drug effects, early use, and continued use. Ultimately, these relations can only be determined from systematic longitudinal studies with comprehensive assessments from early drug responses to progression of problem drug use. In parallel, additional investigation of initial responses in animal models as predictors of drug use will shed light on the underlying mechanisms.

Effects of cold pressor pain on the abuse liability of intranasal oxycodone in male and female prescription opioid abusers

BACKGROUND

Approximately 1.9 million persons in the U.S. have prescription opioid use disorders often with concomitant bodily pain, but systematic data on the impact of pain on abuse liability of opioids is lacking. The purpose of this study was to determine whether pain alters the intranasal abuse liability of oxycodone, a commonly prescribed and abused analgesic, in males and females.

METHODS

Sporadic prescription opioid abusers (10 females, 10 males) participated in this mixed (between and within-subject), randomized inpatient study. Experimental sessions (n=6) tested intranasal placebo, oxycodone 15 or 30 mg/70 kg during cold pressor testing (CPT) and a warm water control. Observer- and subject-rated drug effect measures, analgesia, physiologic and cognitive effects were assessed.

RESULTS

The CPT significantly increased blood pressure, heart rate, pain, stress, and "opiate desire" compared to the no-pain control but did not alter opioid liking, high or street value. Intranasal oxycodone produced effects within 10 min, significantly decreasing pain and significantly increasing subjective measures of abuse liability (e.g., high). Females had higher ratings of street value, high, and liking for one or both active doses.

CONCLUSIONS

The CPT was a reliably painful and stressful stimulus that did not diminish the abuse liability of intranasal oxycodone. Females were more sensitive to oxycodone on several abuse liability measures that warrant further follow-up. Snorting oxycodone rapidly produced psychoactive effects indicative of substantial abuse liability.

Subjective, psychomotor, and physiological effects of oxycodone alone and in combination with ethanol in healthy volunteers

RATIONALE

Nonmedical use of prescription opioids is sometimes accompanied by the ingestion of ethanol. Whether ethanol increases the abuse liability-related effects of prescription opioids has not been determined.

OBJECTIVE

The purpose of this study was to characterize the subjective, psychomotor, and physiological effects of oxycodone, a widely prescribed and abused opioid, and ethanol, alone and in combination.

METHODS

Fourteen volunteers participated in a randomized, crossover trial in which they were exposed to placebo, oxycodone (10 mg), two doses of ethanol (0.3 and 0.6 g/kg), and oxycodone combined with the lower dose and the higher dose of ethanol on separate sessions.

RESULTS

Several abuse liability-related subjective effects (drug liking, take again, pleasant bodily sensations) were not increased by the low dose of ethanol or oxycodone alone relative to placebo, but were when the two were combined. Self-reported liking of the higher dose of ethanol was higher than that of placebo, but oxycodone neither increased nor decreased this effect. Psychomotor and cognitive performance was not affected by any of the active drug conditions. Absorption of ethanol was decreased by oxycodone.

CONCLUSIONS

In this study, 10 mg of oral oxycodone combined with a low dose of ethanol generated abuse liability-related effects, but when tested separately, they did not. Further psychopharmacological investigations of this combination are warranted in light of these findings and the fact that nonmedical use of prescription opioids is sometimes accompanied by use of ethanol.

Oxycodone lengthens reproductions of suprasecond time intervals in human research volunteers

Oxycodone, a popularly used opioid for treating pain, is widely abused. Other drugs of abuse have been shown to affect time perception, which, in turn, may affect sensitivity to future consequences. This may contribute to continued use. This study evaluated the effect of oxycodone on time perception in normal healthy volunteers. For this within-subject, double-blind design study, participants performed a temporal reproduction task before and after receiving placebo or oxycodone (15 mg, orally) over six outpatient sessions. Participants were first trained with feedback to reproduce three standard intervals (1.1, 2.2, and 3.3 s) in separate blocks by matching response latency from a start signal to the duration of that block's standard interval. During testing, participants were instructed to reproduce the three intervals from memory without feedback before and after drug administration. Oxycodone significantly lengthened time estimations for the two longer intervals relative to placebo. These results suggest that opioids alter temporal processing for intervals greater than 1 s, raising questions about the effect of these drugs on the valuation of future consequences.

Subjective, psychomotor, and physiological effects of pregabalin alone and in combination with oxycodone in healthy volunteers

Pregabalin is an anticonvulsant drug indicated for neuropathic disorders and fibromyalgia. Some chronic pain patients suffering from these disorders take both this drug and an opioid for pain relief. Pregabalin is a scheduled drug under the Controlled Substances Act. The subjective effects of this drug have not been well-characterized, and the extent to which it alters the subjective effects of opioids has not been studied to the best of our knowledge. Using a double-blind, randomized, crossover design, 16 healthy volunteers were administered (in separate sessions) capsules containing placebo, 75 mg pregabalin, 150 mg pregabalin, 10 mg oxycodone, and 75 mg pregabalin combined with 10 mg oxycodone. Subjective, psychomotor, and physiological measures were assessed during each of the five sessions. Pregabalin produced dose-related increases in some subjective effects and decreased respiration rate, but did not impact on psychomotor performance. Abuse liability-related subjective effects such as drug liking and desire to take the drug again were not increased by either pregabalin dose. Oxycodone produced increases in several subjective effects, including ratings of drug liking. When 75 mg pregabalin was combined with oxycodone some subjective effects were altered relative to placebo, in contrast to when each drug was tested alone. Liking of oxycodone was not increased by 75 mg pregabalin. However, recent studies have suggested that this drug is abused, and we would recommend that further psychopharmacological studies with pregabalin are warranted, including a study assessing its abuse liability across a range of doses in sedative abusers.

The subjective, reinforcing, and analgesic effects of oxycodone in patients with chronic, non-malignant pain who are maintained on sublingual buprenorphine/naloxone

Some sources suggest that significant misuse of opioid drugs exists among patients with chronic pain. However, the risk factors and motivation behind their abuse may differ from those of other opioid abusers. This study sought to examine the abuse liability of oxycodone among patients with chronic, non-malignant pain who met the DSM-IV criteria for opioid abuse. Eighteen opioid-dependent patients with chronic pain lived on an in-patient unit of the New York State Psychiatric Institute during the 7-week study. Participants were given oral oxycodone (0, 10, 20, 40, and 60 mg/70 kg) while maintained on various doses of sublingual buprenorphine/naloxone (Bup/Nx; 2/0.5, 8/2, and 16/4 mg/day). Doses of both medications were administered under double-blind conditions. Oxycodone produced an overall positive, but less robust, subjective profile than previously reported in recreational opioid users without pain. Furthermore, unlike our findings in recreational opioid users and more similar to effects in non-drug-abusing individuals, oxycodone failed to serve as a reinforcer. As for the maintenance drug, Bup/Nx produced a dose-related reduction in some of the effects of acutely administered oxycodone. These data suggest that sublingual Bup/Nx has the potential as an analgesic medication and further research should investigate its use in treating patients with chronic pain who abuse opioids.

Intravenous oxycodone, hydrocodone, and morphine in recreational opioid users: abuse potential and relative potencies

RATIONALE

Nonmedical use and abuse of prescription opioids is an increasing public health problem. Intravenous (IV) administration of opioid analgesics intended for oral use is not uncommon; yet, little is known about the relative abuse potential of these drugs when administered intravenously to recreational opioid abusers without physical dependence.

METHODS

This inpatient study employed a double-blind, randomized, within-subject, placebo-controlled design to examine the relative abuse potential of IV doses of oxycodone, hydrocodone, and morphine. Nine healthy adult participants reporting recreational opioid use and histories of IV opioid use completed 11 experimental sessions, including one active-dose practice session. IV doses were infused over 5 min and included three identical doses of each opioid (5, 10, and 20 mg/10 ml) and saline placebo. Physiological, subjective, and performance effects were collected before and for 6 h after drug administration.

RESULTS

All three opioids produced prototypical mu agonist effects (e.g., miosis; increased ratings of liking) that were generally dose-related. Pharmacodynamic effects were observed within 5 min of IV administration. Physiological effects were more prolonged than subjective effects for all three drugs. While the magnitude of effects was generally comparable across drugs and qualitatively similar, valid potency assays indicated the following potency relationship: oxycodone > morphine > hydrocodone.

CONCLUSIONS

There were modest potency differences between oxycodone, hydrocodone, and morphine, but their overall profile of effects was similar, indicating significant abuse potential when administered intravenously.

Human abuse liability assessment of oxycodone combined with ultra-low-dose naltrexone

RATIONALE

Prescription opioid abuse has risen dramatically in the United States as clinicians have increased opioid prescribing for alleviation of both acute and chronic pain. Opioid analgesics with decreased risk for abuse are needed.

OBJECTIVE

Preclinical and clinical studies have shown that opioids combined with ultra-low-dose naltrexone (NTX) may have increased analgesic potency and have suggested reduced abuse or dependence liability. This study addressed whether addition of ultra-low-dose naltrexone might decrease the abuse liability of oxycodone (OXY) in humans.

MATERIALS AND METHODS

This double-blind, placebo-controlled study systematically examined the subjective and physiological effects of combining oral OXY and ultra-low NTX doses in 14 experienced opioid abusers. Seven acute drug conditions given at least 5 days apart were compared in a within-subject crossover design: placebo, OXY 20 mg, OXY 40 mg, plus each of the active OXY doses combined with 0.0001 and 0.001 mg NTX.

RESULTS

The methods were sensitive to detecting opioid effects on abuse liability indices, with significant differences between all OXY conditions and placebo as well as between 20 and 40 mg OXY doses on positive subjective ratings (e.g., "I feel a good drug effect" or "I like the drug"), on observer- and participant-rated opioid agonist effects, and on a drug-versus-money value rating. There were no significant differences or evident trends associated with the addition of either NTX dose on any abuse liability indices.

CONCLUSIONS

The addition of ultra-low-dose NTX to OXY did not decrease abuse liability of acutely administered OXY in experienced opioid abusers.

Abuse liability of oxycodone as a function of pain and drug use history

The relationship between pain and prescription opioid abuse is poorly understood. Determining whether a patient is seeking additional opioid medications in order to alleviate pain or to abuse the drugs can be difficult. The present study was designed to evaluate two variables that may influence the abuse liability of opioids: drug use history and the presence or absence of experimentally induced pain. Eighteen healthy participants completed this outpatient study. One group was abusing prescription opioids (N=9) and one group had used prescription opioids medically but did not abuse them (N=9). All participants completed twelve sessions during which the effects of orally delivered oxycodone (0, 15, 30mg/70kg, PO) were examined. One dose was tested per day under double-blind conditions and sessions were separated by at least 48h. During the first "sample" session each week, participants were given $10 and the dose that was available later that week. During the second "choice" session, participants could self-administer either money or the previously sampled dose. Six sessions involved repeated hand immersions in cold water (4 degrees C) and six sessions involved immersions in warm water (37 degrees C). Most of the positive subjective effects of oxycodone were similar between the groups, but oxycodone self-administration significantly differed between groups. Non-abusers self-administered active doses of oxycodone only when they were in pain while abusers self-administered oxycodone regardless of the pain condition. These data suggest that an assessment of the reinforcing effects of opioids may be a sensitive method for differentiating opioid abusers from non-abusers.

Psychopharmacological effects of oxycodone in healthy volunteers: roles of alcohol-drinking status and sex

BACKGROUND

Studies have shown that alcohol-drinking status modulates psychopharmacological effects of several drugs. We sought to determine if drinking status modulates the effects of a prescription opioid, oxycodone, in healthy volunteers. We included sex of the volunteer in the statistical analyses since this is a factor that is known to alter several pharmacodynamic effects of opioids in nonhumans and humans.

METHODS

Fifteen light drinkers (eight males) and 14 moderate drinkers (eight males) participated in a crossover, randomized, double-blind study in which they received 0, 10, and 20mg of oxycodone (p.o.). Dependent measures were subjective, psychomotor/cognitive, reinforcing, and physiological effects.

RESULTS

Self-reported alcohol-drinking status did not modulate the effects of oxycodone. However, there were a number of Sex x Dose interactions with females reporting more and larger unpleasant effects than males (e.g., visual analog scale ratings of "nauseated" greater in females than in males).

CONCLUSIONS

Studies have established that moderate drinkers report a greater degree of abuse liability-related effects than do light drinkers with several different drugs, including diazepam, amphetamine, and nitrous oxide, but we were unable to establish this with the prescription opioid, oxycodone. However, we did observe sex differences in several subjective effects of oxycodone, a finding that is consistent with the extant literature showing sex differences in pharmacodynamic effects of opioids.

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.

A possible link between sensation-seeking status and positive subjective effects of oxycodone in healthy volunteers

Sensation-seeking is a personality trait that is linked to use and abuse of drugs. Laboratory studies have established that high sensation seekers, as measured by different instruments, are more likely to report abuse liability-related subjective effects from drugs such as nicotine, alcohol, and d-amphetamine than low sensation seekers. One class of drugs that has not been studied to date in this fashion is opioids. Accordingly, a retrospective analysis encompassing five studies that examined oxycodone effects, including its abuse liability-related effects, was conducted in subjects categorized as high or low sensation seekers. In addition, because there appear to be sex differences in how males and females respond to opioids, this factor was taken into account in the analysis. Seventy one subjects who scored on the lower end (15 and 19 low sensation-seeking males and females, respectively) or the higher end (23 and 14 high sensation-seeking males and females) of the Disinhibition subscale of the Sensation-Seeking Scale-Form V were studied for their responses to 0, 10, and 20mg of oral oxycodone. Ratings of "pleasant bodily sensations" were significantly higher after oxycodone administration than placebo only in male and female high sensation seekers. Ratings of "take again," "drug liking," "carefree," and "elated (very happy)" also tended to differentiate high from low sensation seekers although Group x Dose interactions were only marginally significant with the latter three ratings. Male and female low sensation seekers and female high sensation seekers reported dysphoric effects (e.g., ratings of nauseated) particularly after administration of the 20mg oxycodone dose. The results of this analysis provide suggestive evidence that high sensation seekers are more likely to experience greater positive subjective effects from oxycodone than low sensation seekers, but likelihood of experiencing negative effects is more complex (involving both sensation-seeking status and sex).

The prescription opioid, oxycodone, does not alter behavioral measures of impulsivity in healthy volunteers

This study examined the effects of oral oxycodone, a prescription opioid, on several measures of impulsive behavior in healthy volunteers. Volunteers (n=12) participated in a four-session, double-blind, randomized design in which they received capsules containing oxycodone (5, 10, and 20 mg) or placebo. From 70 min to approximately 120 min after ingesting the capsules, subjects completed five impulsivity tasks: delay and probability discounting task, balloon analogue risk task (BART), go/no-go task, stop task, and simple reaction time test. Mood questionnaires were also completed at fixed time points in the sessions. Oxycodone produced prototypic changes in mood in a dose-related manner, but did not affect performance on any of the impulsivity tasks. Lack of effect on impulsivity stands in contrast to other studies in which other psychoactive drugs including ethanol, delta-9-tetrahydrocannabinol, and amphetamine altered behavior on one or more behavioral measures of impulsivity.

Putative human pheromone androstadienone attunes the mind specifically to emotional information

The putative human pheromone Delta4,16-androstadien-3-one (androstadienone), a non-androgenic steroid found in sweat and saliva, modulates psychological, physiological and hormonal responses without detection as an odor. To determine the specific psychological processes altered by androstadienone, four studies were completed by 50 men and women after solutions of 250 microM androstadienone or clove-odor control carrier, on separate days, were applied to their upper lip: (1) face pairs were subliminally presented, with one face neutral and the other happy or angry. Androstadienone accelerated speed to locate a subsequent dot probe appearing on the same side as emotional faces, without affecting overall reaction times, indicating that androstadienone specifically enhanced automatic attention to emotional information. (2) In two Stroop paradigms, emotional or mismatched color words interfered with ink color identification. Androstadienone slowed ink color identification of emotional words, demonstrating greater allocation of attentional resources towards emotional information, with no effect on the cognitive Stroop. (3) To test effects on social cognition, participants performed two working memory tasks with distinct stimuli, neutral faces or shapes. Androstadienone did not alter attention to either the social or nonsocial images. (4) The ameliorative effects of androstadienone on self-reported attentiveness were replicated, consistent with increased attention to emotional visual stimuli. Moreover, androstadienone did not alter positive or negative mood, as participants were alone during testing, which removed emotional stimuli from social interactions with a tester. Taken together, these findings demonstrate that subliminal androstadienone guides psychological resources to specifically engage stimuli with emotional significance and does not alter attention to social or general cognitive information.

Within-subject comparison of the psychopharmacological profiles of oral hydrocodone and oxycodone combination products in non-drug-abusing volunteers

BACKGROUND

Non-medical use and abuse of prescription opioids is a significant problem in the United States. Little attention has been paid to assessing the relative psychopharmacological profile (including abuse liability-related effects) of specific prescription opioids. The purpose of this study was to directly compare the psychopharmacological profile of two widely prescribed and abused oral opioid combination products within the same subject.

METHODS

Twenty non-drug-abusing volunteers participated in a crossover, randomized, double-blind study in which they received, all p.o.: placebo; 975 mg acetaminophen (ACET); 10mg oxycodone (OXY)/487 mg ACET; 20mg OXY/975 mg ACET; 15 mg hydrocodone (HYD)/487 mg ACET; and 30mg HYD/975 mg ACET. OXY and HYD doses were chosen to equate the drugs on an objective measure of opiate effects: miosis. Dependent measures were subjective, psychomotor/cognitive, reinforcing, and physiological effects, and relative potency estimates.

RESULTS

In general, the two opioid combination products at equi-miotic doses produced similar prototypic opiate-like effects and psychomotor impairment, and of similar magnitude. The higher dose of OXY/ACET produced slightly more abuse liability-related subjective effects than the higher dose of HYD/OXY, but also produced slightly more negative effects. Neither drug at either dose functioned as a reinforcer, as measured by the Multiple Choice Procedure. Relative potency ratios indicated that OXY/ACET was approximately 1.5 times more potent than HYD/ACET.

CONCLUSIONS

Consistent with a recent study published in this journal using identical doses of HYD and OXY (without ACET) in prescription opioid abusers (Walsh, S.L., Nuzzo, P.A., Lofwall, M.R., Holtman Jr., J.R., 2008. The relative abuse liability of oral oxycodone, hydrocodone and hydromorphone assessed in prescription drug abusers. Drug Alcohol Depend. 198, 191-202), we found little difference in the pharmacodynamic effects of HYD/ACET and OXY/ACET in non-drug-abusing volunteers.

The relative abuse liability of oral oxycodone, hydrocodone and hydromorphone assessed in prescription opioid abusers

Abuse of prescription opioids has risen precipitously in the United States. Few controlled comparisons of the abuse liability of the most commonly abused opioids have been conducted. This outpatient study employed a double-blind, randomized, within-subject, placebo-controlled design to examine the relative abuse potential and potency of oral oxycodone (10, 20 and 40 mg), hydrocodone (15, 30 and 45 mg), hydromorphone (10, 17.5 and 25mg) and placebo. Healthy adult volunteers (n=9) with sporadic prescription opioid abuse participated in 11 experimental sessions (6.5h in duration) conducted in a hospital setting. All three opioids produced a typical mu opioid agonist profile of subjective (increased ratings of liking, good effects, high and opiate symptoms), observer-rated, and physiological effects (miosis, modest respiratory depression, exophoria and decrements in visual threshold discrimination) that were generally dose-related. Valid relative potency assays revealed that oxycodone was roughly equipotent to or slightly more potent than hydrocodone. Hydromorphone was only modestly more potent (less than two-fold) than either hydrocodone or oxycodone, which is inconsistent with prior estimates arising from analgesic studies. These data suggest that the abuse liability profile and relative potency of these three commonly used opioids do not differ substantially from one another and suggest that analgesic potencies may not accurately reflect relative differences in abuse liability of prescription opioids.

Subjective, psychomotor, and physiological effects profile of hydrocodone/acetaminophen and oxycodone/acetaminophen combination products

OBJECTIVES

To compare within the same individuals two typically prescribed doses of hydrocodone/acetaminophen and oxycodone/acetaminophen products for their subjective, psychomotor, and physiological effects in healthy volunteers.

DESIGN

A randomized, placebo-controlled, double-blind, crossover, six-session clinical laboratory study, enrolling 16 healthy participants (27.2 +/- 4.4 years of age). Participants received 5 mg hydrocodone/325 mg acetaminophen, 10 mg hydrocodone/650 mg acetaminophen, 5 mg oxycodone/325 mg acetaminophen, 10 mg oxycodone/650 mg acetaminophen, 650 mg acetaminophen, and placebo in different sessions.

RESULTS

Oxycodone/acetaminophen and hydrocodone/acetaminophen at the 5-mg opioid dose produced few subjective effects and no significant psychomotor impairment. Relative to placebo, the 10-mg oxycodone combination produced a wider spectrum of subjective effects that were statistically significant than did the 10-mg hydrocodone combination. The 10-mg oxycodone combination also produced a greater degree of miosis than the 10-mg hydrocodone combination. Both drug combinations impaired psychomotor performance at the 10-mg opioid dose.

CONCLUSIONS

The results of this study, albeit in pain-free individuals, may inform physicians who prescribe, and pharmacists who dispense, two widely prescribed opioid/acetaminophen combination products on how patients might be feeling from the drugs. Patients prescribed either of the two opioid/acetaminophen combination products may experience a number of subjective effects, including effects that would contraindicate certain activities, and they should be cautioned accordingly. However, this study documented rather large differences in magnitude of subjective effects between 10 mg oxycodone/650 mg acetaminophen and placebo, and physicians and pharmacists, and ultimately patients, should be aware of these differences.

Genetic and early environmental contributions to alcohol's aversive and physiological effects

Genetic and early environmental factors interact to influence ethanol's motivational effects. To explore these issues, a reciprocal cross-fostering paradigm was applied to Fischer and Lewis rats. The adult female offspring received vehicle or the kappa opioid antagonist nor-BNI (1 mg/kg) followed by assessments of conditioned taste aversion (CTA), blood alcohol concentrations (BACs) and hypothermia induced by 1.25 g/kg intraperitoneal ethanol. CTA acquisition in the in-fostered Fischer and Lewis animals did not differ; however, the Fischer maternal environment produced stronger acquisition in the cross-fostered Lewis rats versus their in-fostered counterparts. CTAs in the Fischer rats were not affected by cross-fostering. In extinction, the in-fostered Lewis animals displayed stronger aversions than the Fischer groups on two trials (of 12) whereas the cross-fostered Lewis differed from the Fischer groups on nine trials. Despite these CTA effects, Lewis rats exhibited higher BACs and stronger hypothermic responses than Fischer with no cross-fostering effects in either strain. No phenotypes were affected by nor-BNI. These data extend previous findings dissociating the aversive and peripheral physiological effects of ethanol in female Fischer and Lewis rats, and highlight the importance of genetic and early environmental factors in shaping subsequent responses to alcohol's motivational effects in adulthood.

Acute effects of opioids on memory functions of healthy men and women

INTRODUCTION

Although several psychotropic drugs can acutely induce an anterograde impairment of memory which impedes new learning, they do not produce retrograde impairments, reducing memory for information learned prior to the drug being administered. However, both anterograde and retrograde memory impairments have been reported following an acute dose of morphine in palliative care patients (Kamboj et al., Pain 117:388-395, 2005).

OBJECTIVE

The present study was designed to determine: (1) whether similar amnestic effects would be found after a single oral dose of either morphine or oxycodone in healthy volunteers, (2) how generalisable such effects were across a broader range of memory tasks and (3) whether men and women showed a differential response.

MATERIALS AND METHODS

A double-blind, placebo-controlled crossover design was used with 18 participants (nine men, nine women) who were administered 10 mg morphine, 5 mg oxycodone and placebo on three separate test days.

RESULTS

On a working memory task, subtle impairments were found in women following both opioids whilst in men only following morphine. On an episodic memory task, women made significantly more source attribution errors after oxycodone and men made more after placebo. Most gender differences were weight related and a range of other measures showed no drug-induced impairments.

CONCLUSION

We conclude that these standard doses of opioids have only marginal effects on memory. If these findings can be extrapolated to patients with pain, then clinicians can feel confident in prescribing them on an outpatient basis without impacting on patients' daily functioning.

Abuse liability of prescription opioids compared to heroin in morphine-maintained heroin abusers

Abuse of prescription opioid medications has increased dramatically in the United States during the past decade, as indicated by a variety of epidemiological sources. However, few studies have systematically examined the relative reinforcing effects of commonly abused opioid medications. The current double-blind, placebo-controlled in-patient study was designed to compare the effects of intravenously delivered fentanyl (0, 0.0625, 0.125, 0.187, and 0.250 mg/70 kg), oxycodone (0, 6.25, 12.5, 25, and 50 mg/70 kg), morphine (0, 6.25, 12.5, 25, and 50 mg/70 kg), buprenorphine (0, 0.125, 0.5, 2, and 8 mg/70 kg), and heroin (0, 3.125, 6.25, 12.5, and 25 mg/70 kg) in morphine-maintained heroin abusers (N=8 completers maintained on 120 mg per day oral morphine in divided doses (30 mg q.i.d.)). All of the participants received all of the drugs tested; drugs and doses were administered in non-systematic order. All of the drugs produced statistically significant, dose-related increases in positive subjective ratings, such as 'I feel a good drug effect' and 'I like the drug.' In general, the order of potency in producing these effects, from most to least potent, was fentanyl>buprenorphine>or=heroin >morphine=oxycodone. In contrast, buprenorphine was the only drug that produced statistically significant increases in ratings of 'I feel a bad drug effect' and it was the only drug that was not self-administered above placebo levels at any dose tested. These data suggest that the abuse liability of buprenorphine in heroin-dependent individuals may be low, despite the fact that it produces increases in positive subjective ratings. The abuse liabilities of fentanyl, morphine, oxycodone, and heroin, however, appear to be similar under these experimental conditions.

Within-subject comparison of the psychopharmacological profiles of oral oxycodone and oral morphine in non-drug-abusing volunteers

RATIONALE

Nonmedical use and abuse of prescription opioids is a significant problem in the USA. Little attention has been paid to assessing the relative psychopharmacological profile (including abuse liability-related effects) of specific prescription opioids.

OBJECTIVES

The aim of this study is to directly compare the psychopharmacological profile of two oral opioids within the same subject.

METHODS

A randomized, placebo-controlled, crossover study was done in which 20 non-drug-abusing volunteers ingested 10 and 20 mg of oxycodone, 30 and 60 mg of morphine, and placebo in separate sessions. Drug doses were equated on an objective measure of opiate effects: miosis. Subjective, psychomotor, reinforcing, and physiological effects of the opioids were assessed.

RESULTS

In general, the two opioids at equimiotic doses produced similar prototypic opiate-like effects and psychomotor impairment of similar magnitude. However, several effects were found only with 20 mg oxycodone. Both drugs produced abuse liability-related subjective effects but also dysphoric effects, particularly with 60 mg morphine. Neither drug at either dose functioned as a reinforcer, as measured by the Multiple Choice Procedure. Relative potency ratios indicated an average oxycodone/morphine [corrected] ratio of 1:3 [corrected]

CONCLUSIONS

The psychopharmacological profile of oxycodone and morphine at equimiotic doses had many similarities; however, differences were found in producing abuse liability-related and dysphoric effects. In the medical community, it is commonly accepted that oral oxycodone is 1.5 to 2 times as potent as oral morphine in producing analgesia; using this ratio, although patients may experience similar degrees of pain relief, those receiving oxycodone may be experiencing stronger and potentially different psychopharmacological effects.

Early maternal separation and sex differences in the aversive effects of amphetamine in adult rats

Early life stress increases vulnerability to psychostimulant abuse, sometimes in a sex-dependent manner. These effects are presumably produced by modulation of neurobiological reward mechanisms; however, drug intake is also influenced by sensitivity to the drug's aversive properties, and little is known about the effects of early life stress on stimulant aversion. To assess this possibility, Sprague-Dawley rat litters experienced daily separation from the dam for 3 h (MS) or 15 min (H) on post-natal days 2-14; control litters (AFR) experienced twice-weekly routine animal facility care only. As adults, the animals were tested for conditioned taste aversions (CTA) induced by 1.5, 2.0 or 3.0 mg/kg d-amphetamine administered intraperitoneally over three acquisition trials followed by six drug-free extinction trials (n=7-8/sex/dose/rearing group). All groups acquired significant aversions compared to their vehicle-treated controls, but differential rearing had no effect on CTA acquisition or extinction. Collapsed across rearing groups, females exhibited significantly stronger aversions and slower extinction than their male counterparts at the low 1.5 mg/kg dose, and unlike the males, failed to fully extinguish relative to their vehicle controls at 1.5 and 2.0 mg/kg. These data underscore the importance of sex differences in assays of stimulant abuse liability, and further support the hypothesis that the effects of post-natal stress on the reinforcing efficacy of psychostimulants may be predominantly due to modulation of reward mechanisms.

Open-label study of the safety and effectiveness of long-term therapy with extended-release tramadol in the management of chronic nonmalignant pain

BACKGROUND

Tramadol ER* is a once-daily oral analgesic for management of moderate-to-moderately severe chronic pain in adults who require around-the-clock treatment of pain. This study evaluated long-term safety of tramadol ER and effectiveness outcomes in the management of chronic, nonmalignant pain.

METHODS

Patients enrolled directly for approximately 1 year of open-label tramadol ER treatment if they had chronic, nonmalignant pain (n = 919), or 'rolled over' for 38 weeks of open-label tramadol ER treatment if they completed either of two 12-week, placebo-controlled studies of tramadol ER for low back pain (n = 72) or osteoarthritis (n = 61). Tramadol ER was titrated to a dose of 300 mg once daily (patients >or= 75 years) or 300-400 mg once daily (patients < 75 years).

RESULTS

A total of 257 (24%) patients completed the study. Common adverse events, regardless of treatment relationship, were nausea, dizziness (excluding vertigo), and constipation. Mean scores for current pain intensity (from 0 = no pain to 100 = extreme pain) and least, worst, and average pain intensity over the past week improved at every post-baseline visit. At each post-baseline visit, > 50% of patients provided a global assessment rating of good, very good, or excellent. Study limitations were mandatory titration to 400 mg in some patients, concomitant analgesic therapy as a confounding variable, and lack of a placebo comparator.

CONCLUSIONS

Individualized dose titration and limiting once-daily therapy with tramadol ER to the maximum recommended daily dose of 300 mg may balance tolerability and analgesic effects of tramadol ER in patients with chronic, nonmalignant pain.

Neuropsychological Consequences of Opiate Use

Approximately 3.7 million individuals have used heroin and other opiate substances in their lifetime. Despite increasing knowledge of the effects of heroin, it remains the most abused opiate and use among adults has recently increased. The empirical literature examining the neurocognitive effects of acute and chronic opioid use remains limited; however, findings to date suggest that the use of opiates has both acute and long-term effects on cognitive performance. Neuropsychological data indicate deficits in attention, concentration, recall, visuospatial skills and psychomotor speed with both acute and chronic opioid use. The long-term effects of opiate use appear to have the greatest impact on executive functions, including the ability to shift cognitive set and inhibit inappropriate response tendencies. Factors that contribute to addiction and recovery are also discussed, as it is difficult to disentangle the effects of opiate use on cognitive performance from other factors that may affect neurobehavioral measures.

Psychoactive drug abuse in older adults

BACKGROUND

Misuse and abuse of legal and illegal drugs constitute a growing problem among older adults.

OBJECTIVE

This article reviews the prevalence, risks and protective factors, and screening and diagnosis of drug abuse in older adults. Treatment concerns and the consequences of drug problems are examined briefly.

METHODS

MEDLINE and PsychInfo were searched using the terms substance-related disorders, drug-use disorders, abuse, dependency, opioid-related disorders, stimulant-related disorders, cocaine-related disorders, marijuana-related disorders, and withdrawal syndrome. The review included articles published in English between January 1, 1990, and May 31, 2006.

RESULTS

Despite a wealth of information on the epidemiology and treatment of alcohol abuse in older adults, few comparable data are available on drug abuse in this population. The evidence suggests that although illegal drug use is relatively rare among older adults compared with younger adults and adolescents, there is a growing problem of the misuse and abuse of prescription drugs with abuse potential. It is estimated that up to 11% of older women misuse prescription drugs and that nonmedical use of prescription drugs among all adults aged > or =50 years will increase to 2.7 million by the year 2020. Factors associated with drug abuse in older adults include female sex, social isolation, history of a substance-use or mental health disorder, and medical exposure to prescription drugs with abuse potential. No validated screening or assessment instruments are available for identifying or diagnosing drug abuse in the older population. Special approaches may be necessary when treating substance-use disorders in older adults with multiple comorbidities and/or functional impairment, and the least intensive approaches should be considered first.

CONCLUSIONS

Psychoactive medications with abuse potential are used by at least 1 in 4 older adults, and such use is likely to grow as the population ages. The treatment of disorders of prescription drug use in older adults may involve family and caretakers, and should take into account the unique physical, emotional, and cognitive factors of aging. Further research is needed on the epidemiologic, health services, and treatment aspects of drug abuse in older adults, as well as the development of appropriate screening and diagnostic tools.

Assessment of the aversive and rewarding effects of alcohol in Fischer and Lewis rats

RATIONALE

Application of the Fischer-Lewis genetic model of drug abuse to the study of alcohol's motivational properties has been limited.

OBJECTIVES

To assess the aversive and rewarding effects of ethanol in Fischer and Lewis rats.

MATERIALS AND METHODS

Fischer and Lewis rats underwent a four-trial combined conditioned taste aversion/conditioned place preference procedure (CTA/CPP; 0, 1, 1.25, or 1.5 g/kg IP ethanol). Others received 0, 1, or 1.5 g/kg followed by tail blood sampling at 15-, 60- and 180-min post-injection. In additional groups, hypothermia to 0, 1.5, and 3 g/kg was assessed before and 30- and 60-min post-injection.

RESULTS

All alcohol-treated groups except low-dose Lewis acquired CTA after one trial. Fischer rats developed stronger CTAs than Lewis at 1.25 and 1.5 g/kg. Ethanol-induced reward in taste or place conditioning was not evident in either strain. Lewis animals showed overall higher peak blood alcohol concentrations, but hypothermia did not vary by strain.

CONCLUSION

Compared to Fischer, Lewis rats are less sensitive to alcohol's aversive effects as assessed in the CTA paradigm. The behavioral differences observed are not due to hypothermia, but pharmacokinetic differences may contribute. These data underscore the importance of genetic factors and the aversive effects of initial drug exposures in modeling vulnerability to abuse. In addition to its application with other drugs, the Fischer-Lewis model may be useful for investigating the biobehavioral bases of alcohol abuse.

Effects of an opioid (oxycodone/paracetamol) and an NSAID (bromfenac) on driving ability, memory functioning, psychomotor performance, pupil size, and mood

OBJECTIVE

It has been suggested that driving a car is relatively safe when the driver is treated with nonsteroid anti-inflammatory drugs than when he or she is treated with opioid analgesics. However, the evidence for this statement is scarce. The objective of this study was to determine the effects of a nonsteroid anti-inflammatory drug (bromfenac 25 mg and 50 mg) and an opioid (oxycodone/paracetamol 5/325 mg and 10/650 mg), and placebo on driving ability, memory functioning, psychomotor performance, pupil size, and mood.

METHODS

Out of 30 healthy volunteers, 18 completed this randomized, double-blind, placebo-controlled crossover study, before the study had to be stopped due to bromfenac being pulled out from the market. One hour after administration of the drugs, the participants performed a standardized driving test during normal traffic. Thereafter, driving quality, mental effort and mental activation during driving were assessed. A laboratory test battery was performed 2.5 hours after administration of the drug. Visual analog scales assessing mood and pupil measurements were performed on several occasions during each test day.

RESULTS

Both analgesics did not significantly affect performance in any test. However, volunteers reported that significantly more effort was needed to perform the driving test when treated with oxycodone/paracetamol, and that they experienced increased sedation and reduced alertness. Also, the pupil size was significantly decreased. In contrast, subjective assessments after both doses of bromfenac matched that of placebo.

DISCUSSION

No significant impairment in behavior was found in the volunteers for both bromfenac and oxycodone/paracetamol. The lack of impairment from oxycodone/paracetamol may have been related to the participants reporting increased effort during driving while under the influence of this drug.

Abuse of prescription drugs and the risk of addiction

Abuse of several categories of prescription drugs has increased markedly in the United States in the past decade and is now at alarming levels for certain agents, especially opioid analgesics and stimulants. Prescription drugs of abuse fit into the same pharmacological classes as their non-prescription counterparts. Thus, the potential factors associated with abuse or addiction versus safe therapeutic use of these agents relates to the expected variables: dose, route of administration, co-administration with other drugs, context of use, and expectations. Future scientific work on prescription drug abuse will include identification of clinical practices that minimize the risks of addiction, the development of guidelines for early detection and management of addiction, and the development of clinically effective agents that minimize the risks for abuse. With the high rates of prescription drug abuse among teenagers in the United States, a particularly urgent priority is the investigation of best practices for effective prevention and treatment for adolescents, as well as the development of strategies to reduce diversion and abuse of medications intended for medical use.

Major increases in opioid analgesic abuse in the United States: concerns and strategies

The problem of abuse of and addiction to opioid analgesics has emerged as a major issue for the United States in the past decade and has worsened over the past few years. The increases in abuse of these opioids appear to reflect, in part, changes in medication prescribing practices, changes in drug formulations as well as relatively easy access via the internet. Though the use of opioid analgesics for the treatment of acute pain appears to be generally benign, long-term administration of opioids has been associated with clinically meaningful rates of abuse or addiction. Important areas of research to help with the problem of opioid analgesic abuse include the identification of clinical practices that minimize the risks of addiction, the development of guidelines for early detection and management of addiction, the development of opioid analgesics that minimize the risks for abuse, and the development of safe and effective non-opioid analgesics. With high rates of abuse of opiate analgesics among teenagers in the United States, a particularly urgent priority is the investigation of best practices for treating pain in adolescents as well as the development of prevention strategies to reduce diversion and abuse.

Characterization of the antinociceptive effect of oxycodone in male and female rats

A number of investigators have shown that sex plays an important role in the analgesic effects of opioids. Typically, the antinociceptive responsiveness to mu opioid agonists such as morphine is greater in male than in female rats. The effect of sex on kappa opioid analgesia is less known. The present study was conducted to examine sex-related differences in responsiveness to oxycodone (putative kappa/mu opioid agonist). This information is important since oxycodone is widely used clinically for treatment of pain. The present results indicated that oxycodone had a greater antinociceptive response in female rats compared to male rats. This sex specific responsiveness to oxycodone, however, was lost with chronic administration. The greater antinociception in female rats was even more prominent with U50,488H (selective kappa agonist). Further, low (subanalgesic) doses of oxycodone and U50,488H enhanced the sensitivity to pain (hyperalgesia) to a greater extent in male than in female rats. This is in contrast to the previously shown greater hyperalgesic effect of subanalgesic doses of the mu opioid agonist, morphine, in female than in male rats. The present findings suggest that sexual dimorphism in the effect of opioids is related to the opioid receptors on which they predominately act.

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.

Endogenous opiates and behavior: 2003

This paper is the 26th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2003 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

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.