Preference for an Opioid/Benzodiazepine Mixture over an Opioid Alone Using a Concurrent Choice Procedure in Rhesus Monkeys

Attenuation of the Positive-Reinforcing Effects of Ultra-Potent Fentanyl Analogs, Along with Those of Fentanyl and Heroin, During Daily Treatment with Methocinnamox in Rhesus Monkeys

Without substantial intervention, the opioid crisis is projected to continue, underscoring the need to develop new treatments for opioid use disorder (OUD). One drug under development is the µ opioid receptor antagonist methocinnamox (MCAM), which appears to offer advantages over currently available medications; however, some questions remain about its potential utility, including its ability to block the effects of ultra-potent fentanyl analogs. The goal of this study was to examine its effectiveness in attenuating the abuse-related effects of the fentanyl analogs carfentanil and 3-methylfentanyl in monkeys responding for food or intravenous infusions under a choice procedure. These drugs were compared with fentanyl, heroin, methamphetamine, and cocaine. Food was preferred over saline, and there was a dose-dependent increase in responding for drug over food with no marked decrease in response rates or number of choice trials completed for any of the six drugs studied. Naltrexone (0.032 mg/kg) antagonized choice of µ opioid receptor agonists, producing rightward shifts in dose-effect curves ranging from 27-fold (carfentanil) to 71-fold (heroin). In contrast, naltrexone was less effective in attenuating choice of methamphetamine or cocaine with curves obtained in the presence of naltrexone shifted <3-fold. Daily treatment with 0.032 mg/kg MCAM also antagonized the effects of opioids, shifting curves 20-fold (fentanyl) to 72-fold (heroin) rightward; MCAM did not significantly change dose-effect curves for methamphetamine or cocaine. Thus, antagonism by MCAM is similar across a variety of µ opioid receptor agonists, including ultra-potent fentanyl analogs, further supporting its potential utility as a treatment for OUD. SIGNIFICANCE STATEMENT: Treatments for opioid use disorder (OUD) should attenuate the effects of a variety of opioids, including emerging threats like the ultra-potent fentanyl analogs. The novel µ opioid receptor antagonist MCAM is being developed to treat OUD because it provides long-lasting blockade of the reinforcing effects of heroin and fentanyl. The current study shows that MCAM attenuates the abuse-related effects of the fentanyl analogs carfentanil and 3-methylfentanyl, further supporting the utility of MCAM as a treatment for OUD.

Self-Administration of Fentanyl-Alprazolam Combinations by Rhesus Monkeys Responding under a Progressive-Ratio Schedule

This study evaluated the reinforcing effects of fentanyl, alone or in combination with the benzodiazepine alprazolam, in rhesus monkeys (3 females, 3 males). Subjects were trained to self-administer the opioid remifentanil (0.3 µg/kg/injection) under a progressive-ratio schedule of reinforcement. The reinforcing effects of fentanyl (0.1-10 µg/kg/injection) or alprazolam (1.0-100 µg/kg/injection) alone, or in combinations of fixed proportions (1:1, 1:3, and 3:1 fentanyl:alprazolam, with 1:1 based on the potencies of drugs alone) were evaluated in single-day test sessions (with double determinations). Dose-equivalence analysis was used to determine the extent to which fentanyl and alprazolam combinations differed from additivity. Fentanyl functioned as a positive reinforcer in all monkeys, while alprazolam was a reinforcer in 3 of 6 monkeys only. Therefore, drug combination data were grouped as "alprazolam-taking" and "non-alprazolam-taking" monkeys. For alprazolam-taking monkeys, we observed additive effects for the 3:1 and 1:3 combinations, and a significant supra-additive interaction for the 1:1 combination of fentanyl and alprazolam. For 2 of the 3 non-alprazolam-taking monkeys, the combination of fentanyl and alprazolam resulted in enhanced reinforcing effects relative to either drug alone. However, the one monkey showed primarily inhibitory, or suppressive effects, with the 3:1 dose combination resulting in a relatively modest rightward shift in the fentanyl dose-response function. In summary, our findings show that combining fentanyl and alprazolam generally result in proportion-dependent additive or supra-additive enhancements. These data raise the possibility that the prevalence of opioid-benzodiazepine polydrug abuse may reflect a unique enhancement of these drugs' reinforcing effects, although individual differences may exist. SIGNIFICANCE STATEMENT: Addressing the critical question of the degree to which benzodiazepines can modulate the abuse-related effects of opioids may provide improved pathways to treatment of this common form of polydrug addiction. In the present study, we show that combinations of the opioid fentanyl and the benzodiazepine alprazolam can be more reinforcing than either drug alone in a rhesus monkey model, suggesting that enhancement of reinforcement processes may underlie this prevalent form of polydrug use disorder.

Effects of buprenorphine/lorcaserin mixtures on preference for heroin, cocaine, or saline over food using a concurrent choice procedure in rhesus monkeys

BACKGROUND

The opioid epidemic continues despite the availability of medications, including buprenorphine, for opioid use disorder (OUD); identifying novel and effective treatments is critical for decreasing the prevalence of OUD and ending this crisis. Buprenorphine alone does not markedly attenuate abuse-related effects of nonopioids. Treatment outcomes might be improved by combining buprenorphine with a second medication targeting substance use disorder (SUD), such as lorcaserin, a serotonin_2C (5-HT_2C) receptor selective agonist that decreases abuse-related effects of drugs from several pharmacological classes in preclinical studies.

METHODS

This study investigated the effectiveness of buprenorphine/lorcaserin mixtures to decrease preference for heroin or cocaine in monkeys choosing between food and i.v. infusions.

RESULTS

When saline was available for self-administration, monkeys chose food; when heroin or cocaine was available, monkeys dose-dependently increased choice of infusions. Noncontingent administration of heroin, cocaine, or buprenorphine before sessions increased preference for saline over food. Daily noncontingent administration of buprenorphine increased saline choice, decreased heroin choice, and increased variability across monkeys and sessions; preference for cocaine was not altered. Adding lorcaserin to daily treatment reduced variability such that choice of saline and heroin was consistently less than 20%; choice of cocaine did not change.

CONCLUSIONS

Because buprenorphine/lorcaserin mixtures would not likely alter abuse of cocaine, they might not be useful for treating SUDs; nevertheless, mixtures reduced variability and decreased preference for heroin, compared with buprenorphine alone, perhaps suggesting that a different drug mixture, in which buprenorphine is combined with a second, nonopioid drug, might offer advantages over treatment with buprenorphine alone.

Clonazepam: Indications, Side Effects, and Potential for Nonmedical Use

After participating in this activity, learners should be better able to:• Assess the misuse potential of clonazepam• Characterize the nonmedical use of clonazepam• Identify the health problems associated with long-term use of clonazepam ABSTRACT: Clonazepam, a benzodiazepine, is commonly used in treating various conditions, including anxiety disorders and epileptic seizures. Due to its low price and easy availability, however, it has become a commonly misused medication, both in medical and recreational contexts. In this review, we aim to highlight the behavioral and pharmacological aspects of clonazepam and its history following its approval for human use. We examine the circumstances commonly associated with the nonmedical use of clonazepam and raise points of particular concern. Clonazepam, alone or in combination with other psychoactive substances, can lead to unwanted effects on health, such as motor and cognitive impairment, sleep disorders, and aggravation of mood and anxiety disorders. Prolonged use of clonazepam may lead to physical dependence and tolerance. There is therefore a need to find safer therapeutic alternatives for treating seizures and anxiety disorders. Greater awareness of its frequent nonmedical use is also needed to achieve safer overall use of this medication.

GABAA Receptor Subtypes and the Reinforcing Effects of Benzodiazepines in Remifentanil-Experienced Rhesus Monkeys

BACKGROUND

Opioid-use disorder is associated with a high degree of co-abuse with benzodiazepines. While the mechanisms underlying the co-abuse of opioids and benzodiazepines remain unknown, α1 subunit-containing GABA_A receptors may play a critical role in the reinforcing effects of benzodiazepine-type compounds, depending on whether the monkeys have a history of benzodiazepine or stimulant self-administration. The present study extended our prior research by comparing the reinforcing effects of a compound lacking activity at α1 subunit-containing GABA_A receptors with the reinforcing effects of non-selective GABA_A receptor positive allosteric modulators in monkeys with a history of opioid self-administration.

METHODS

The reinforcing effects of L-838,417 (partial intrinsic efficacy at α2, α3, and α5 subunit-containing GABA_A receptors, but no efficacy at α1 subunit-containing GABA_A receptors, i.e., "α1-sparing compound") were compared with those of the non-selective GABA_A receptor partial modulator MRK-696, and non-selective GABA_A receptor full modulators, triazolam and lorazepam, in rhesus monkeys (n = 3) experienced in remifentanil self-administration under a progressive-ratio schedule of intravenous drug injection.

RESULTS

Neither the partial modulator nor the α1-sparing compound were self-administered above vehicle levels. The full modulators triazolam and lorazepam were self-administered significantly above vehicle levels, albeit at lower levels than remifentanil.

CONCLUSIONS

Our findings suggest that relatively high efficacy at one or more GABA_A receptor subtypes is required for a compound to have reinforcing effects in monkeys with a history of remifentanil self-administration, in contrast to monkeys with benzodiazepine or stimulant self-administration histories.

Correlates of Benzodiazepine Use and Adverse Outcomes Among Patients with Chronic Pain Prescribed Long-term Opioid Therapy

OBJECTIVE

To examine the correlates and odds of receiving overlapping benzodiazepine and opioid prescriptions and whether co-prescription was associated with greater odds of falling or visiting the emergency department.

DESIGN

Cross-sectional study.

SETTING

A large private integrated health system and a Veterans Health Administration integrated health system.

SUBJECTS

Five hundred seventeen adults with musculoskeletal pain and current prescriptions for long-term opioid therapy.

METHODS

A multivariate logistic regression model examined correlates of having overlapping benzodiazepine and opioid prescriptions in the year before enrollment in the cross-sectional study. Negative binomial models analyzed the number of falls in the past three months and past-year emergency department visits. In addition to propensity score adjustment, models controlled for demographic characteristics, psychiatric diagnoses, medications, overall comorbidity score, and opioid morphine equivalent dose.

RESULTS

Twenty-five percent (N = 127) of participants had co-occurring benzodiazepine and opioid prescriptions in the prior year. Odds of receiving a benzodiazepine prescription were significantly higher among patients with the following psychiatric diagnoses: anxiety disorder (adjusted odds ratio [AOR] = 4.71, 95% confidence interval [CI] = 2.67-8.32, P < 0.001), post-traumatic stress disorder (AOR = 2.24, 95% CI = 1.14-4.38, P = 0.019), and bipolar disorder (AOR = 3.82, 95% CI = 1.49-9.81, P = 0.005). Past-year overlapping benzodiazepine and opioid prescriptions were associated with adverse outcomes, including a greater number of falls (risk ratio [RR] = 3.27, 95% CI = 1.77-6.02, P = 0.001) and emergency department visits (RR = 1.66, 95% CI = 1.08-2.53, P = 0.0194).

CONCLUSIONS

Among patients with chronic pain prescribed long-term opioid therapy, one-quarter of patients had co-occurring prescriptions for benzodiazepines, and dual use was associated with increased odds of falls and emergency department visits.

Punishment and reinforcement by opioid receptor agonists in a choice procedure in rats

Intravenous (i.v.) drug self-administration remains the 'gold standard' for assessing abuse potential of drugs. Failure of a drug to maintain self-administration might indicate merely the absence of positive-reinforcing effects but might also indicate presence of aversive effects. Sensitivity to aversive effects is thought to affect the initiation and maintenance of drug use as well as relapse. Choice procedures are used to study positive-reinforcing effects of drugs and to a much lesser extent to study punishing effects of drugs. Experiment 1 compared the μ-opioid receptor agonist remifentanil (0.001-0.01 mg/kg/infusion), the κ-opioid receptor agonist spiradoline (0.0056-0.056 mg/kg/infusion), and histamine (1.0 mg/kg/infusion) in rats choosing between a food pellet only and an i.v. infusion+a food pellet. To test whether a history with one punishing drug affects the punishing effects of a second drug, experiment 2 compared sensitivity with spiradoline in rats with and without a history of histamine punishment. All rats predominantly chose a pellet alone when histamine+a pellet was the alternative, and they predominantly chose remifentanil+a pellet over a pellet alone. In experiment 2, spiradoline was punishing in rats with a history of histamine punishment but not drug-naive rats. This food choice procedure is sensitive to reinforcing and punishing effects of different drugs in the same subjects, suggesting that the procedure is well-suited for studying drug mixtures (e.g. μ and κ agonists) and the impact of different physiological conditions (e.g. pain) on reinforcement and punishment.

Self-administration of benzodiazepine and cocaine combinations by male and female rhesus monkeys in a choice procedure: role of α1 subunit-containing GABAA receptors

RATIONALE

Compounds lacking efficacy at the α1 subunit-containing GABA_A (α1GABA_A) receptor appear to have reduced abuse potential compared with those having measurable efficacy at this receptor, though their self-administration in nonhuman primates is dependent upon past drug experience.

OBJECTIVES

We used a drug vs. drug choice procedure to evaluate the hypothesis that L-838,417, a compound lacking efficacy at αGABA_A receptors, would not enhance cocaine choice in monkeys trained to self-administer cocaine. We also hypothesized that zolpidem, a compound with preferential modulation of ⍺1GABA_A receptors and midazolam, a nonselective benzodiazepine, would enhance cocaine choice in this procedure.

METHODS

One female and three male rhesus monkeys chose between cocaine alone (0.1 mg/kg/injection) vs. the same dose of cocaine combined with midazolam (0.003-0.1 mg/kg/injection), zolpidem (0.003-0.3 mg/kg/injection), or L-838-417 (0.01-0.1 mg/kg/injection). In addition, we evaluated choice between saline and L-838,417 at select doses to determine whether L-838,417 would function as a reinforcer on its own.

RESULTS

Consistent with our hypotheses, midazolam- and zolpidem-cocaine mixtures were chosen over cocaine alone at sufficiently high doses. However, L-838,417-cocaine mixtures also were chosen over cocaine alone in three of four subjects with at least one dose. When available alone vs. saline, L-838,417 did not function as a reinforcer in any subject.

CONCLUSION

Compounds that lack efficacy at α1GABA_A receptors may have low abuse potential compared to classic benzodiazepines, but self-administration of these compounds is context-dependent.

Effects of the synthetic cannabinoid receptor agonist JWH-018 on abuse-related effects of opioids in rhesus monkeys

Opioid abuse remains a public health crisis despite a tremendous outpouring of resources to address the problem. One factor that might complicate this issue is polydrug abuse. While cannabis is increasingly available due to legalization by states, phytocannabinoids do not appear to alter the abuse-related effects of opioids. Synthetic cannabinoids, which are not pharmacologically identical to phytocannabinoids, are also increasingly available, and differences among cannabinoids might affect their interactions with opioids. This study assessed the impact of one synthetic cannabinoid, JWH-018, on the effects of two μ opioid receptor agonists using two procedures that address different aspects of abuse. First, four monkeys could choose to self-administer the opioid remifentanil alone (0.32 μg/kg/infusion) or a mixture containing 0.32 μg/kg/infusion remifentanil and JWH-018 (1-10 μg/kg/infusion). On separate occasions, monkeys could choose between remifentanil available alone or combined with 100 μg/kg/infusion cocaine. While monkeys chose the remifentanil/cocaine mixture over remifentanil alone, they responded equally for remifentanil alone and the remifentanil/JWH-018 mixture. The ability of JWH-018 to reinstate extinguished responding previously maintained by heroin was examined in four other monkeys. When presented with drug-associated stimuli, heroin, but not JWH-018, reinstated responding, and when combined, JWH-018 did not increase the potency of heroin. While opioids and synthetic cannabinoids, including JWH-018, are abused, these results indicate that JWH-018 does not modify the behavioral effects of opioids in monkeys in a manner that would predict greater abuse liability of cannabinoid/opioid mixtures, a result that is consistent with a growing literature on mixtures of opioids and phytocannabinoids.