Pulsed nicotine infusions as a model for smoking: validating a tool to explore nicotine thresholds in humans.

RATIONALE: No previous studies examined the discriminative stimulus effects of intravenous (IV) nicotine in humans. OBJECTIVES: To evaluate a pulsed IV nicotine infusion procedure designed to mimic inhaled nicotine delivery and to identify a range of nicotine doses that may capture the threshold doses for the subjective and discriminative stimulus effects of nicotine. By determining these thresholds, we can gain valuable insights into the addictive threshold of nicotine. METHODS: Eleven participants had 2 Test Sessions following overnight abstinence from smoking. Test Session 1 examined participants' ability to discriminate 0.1 mg nicotine/pulse nicotine from saline. Test Session 2 examined if participants can discriminate 0.05, 0.025, and 0.0125 mg nicotine/pulse of nicotine from saline. These nicotine doses were delivered as a cluster of 4 pulsed-nicotine infusions of 2-second duration with a 28-second interval between each pulse. RESULTS: The lowest doses of nicotine that produced greater responses than saline for discrimination, subjective effects, and heart rate ranged from 0.05 to 0.1 mg nicotine/pulse. CONCLUSIONS: These findings support the validity of our pulsed-infusion procedure as a model for nicotine delivery by smoking and its utility in examining factors that may impact the addictive threshold of nicotine.

Threshold for the pleasurable effects of nicotine are lower than its reinforcing effects during self-administration.

A recent study demonstrated that during a single sampling period, 0.1 mg of intravenous (IV) nicotine (vs. placebo) was found to be the threshold for subjective and physiological drug effects. The present study is a secondary analysis evaluating whether the threshold for subjective and physiological effects is similar when the subject has repeated opportunities to choose blinded doses of nicotine versus placebo. We also examined whether cigarette craving, withdrawal, and rate of nicotine metabolism affected nicotine reinforcement, defined by a greater number of nicotine choices than placebo. Young adult (n = 34; 68% male), daily smokers had five laboratory sessions after overnight abstinence. After sampling an IV dose of nicotine (0.0125, 0.025, 0.05, 0.1, or 0.2 mg/70 kg) versus saline (placebo), participants completed a nicotine self-administration (NSA) procedure that included 10 opportunities to self-administer IV dose of nicotine or placebo. The threshold for subjective positive effects of nicotine during the NSA was equal to or lower than the sampling period, 0.05-0.1 mg versus 0.1 mg. The threshold for nicotine-induced heart rate increase was higher during the NSA than during the sampling period (0.2 mg vs. 0.1 mg). Higher baseline craving and nicotine metabolite ratio (NMR) were associated with nicotine reinforcement at 0.2 mg and 0.1 mg doses, respectively (p < .05). The results suggest that subjective effects during NSA are reported at doses lower than the sampling period. Taken together, tobacco products thought to be subthreshold for reinforcement should be carefully evaluated for their subjective effects, including their discriminative stimulus effects. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Development of pulsed intravenous nicotine infusions as a model for inhaled nicotine in humans.

RATIONALE: Although nicotine from cigarettes is delivered in puff-sized amounts, most preclinical and human intravenous (IV) nicotine studies have used bolus or continuous infusions. OBJECTIVES: To determine the feasibility of a pulsed-nicotine infusion model in smokers. METHODS: Following overnight abstinence, 12 adult smokers underwent 5 laboratory sessions. Using a crossover design, in each session, participants were assigned to 1 of 5 conditions: (1) high/fast: 1.0 mg nicotine delivered over 5 pulsed-infusions, then 15 saline infusions; (2) high/slow: 1.0 mg nicotine delivered over 20 pulsed-infusions; (3) low/fast: 0.2 mg nicotine delivered over 5 pulsed-infusions, then 15 saline infusions; (4) low/slow: 0.2 mg nicotine delivered over 20 pulsed-infusions; and (5) placebo: Saline delivered over 20 pulsed-infusions. Subjective drug effects, urges to smoke, nicotine withdrawal, and cognitive performance were measured in each session. RESULTS: Both the high/fast and high/slow conditions were associated with greater "head rush" and "high" (p < 0.05). The high/fast condition also provided greater suppression of urges to smoke and nicotine withdrawal (p < 0.05), indexed by the Questionnaire of Urges to Smoke-Brief, and the Minnesota Nicotine Withdrawal Scale, respectively. The high/fast and high/slow conditions produced greater increases in heart rate (p < 0.01) than saline. Finally, there were no main effects of dosing conditions on cognitive performance, indexed by the continuous performance test. CONCLUSIONS: These findings demonstrate the feasibility of pulsed-nicotine infusions to model nicotine delivery by smoking. This model could inform future studies testing novel smoking cessation therapies and tobacco regulatory studies testing the impact of nicotine reduction approaches.

Opioid-induced analgesia among persons with opioid use disorder receiving methadone or buprenorphine: A systematic review of experimental pain studies.

BACKGROUND: Treating acute pain among persons with opioid use disorder (OUD) on opioid agonist therapy (OAT) is complex, and the therapeutic benefits of opioids remain unclear when weighted against their abuse potential and respiratory depressant effects. METHODS: We conducted a systematic review of experimental pain studies examining opioid-induced analgesia among persons with OUD on OAT. We searched multiple databases from inception to July 30, 2021. Study quality was assessed by previously established validity measures. RESULTS: Nine studies were identified, with a total of 225 participants, of whom 63% were male, and 37% were female. Six studies included methadone-maintained persons with OUD; four studies included buprenorphine-maintained persons with OUD; and three studies included healthy persons as comparison groups. Either additional doses of OAT or other opioids - morphine, oxycodone, hydromorphone, or remifentanil - were administered. In seven studies, persons with OUD on OAT did not experience analgesia, despite receiving opioid doses up to 20 times greater than those clinically used to treat severe pain among the opioid naïve. Conversely, in two studies, high-potency opioids did produce analgesia, albeit with greater abuse potential. Notably, persons with OUD on OAT remained vulnerable to respiratory depression. CONCLUSIONS: Although persons with OUD on OAT can derive analgesic effects from opioids, high-potency compounds may be required to achieve clinically significant pain relief. Further, persons with OUD on OAT may remain vulnerable to opioid-induced abuse potential and respiratory depression. Together, these finding have clinical, methodological, and mechanistic implications for the treatment of acute pain in the context of OAT.

The Pharmacology of Buprenorphine Microinduction for Opioid Use Disorder.

Although expanding the availability of buprenorphine-a first-line pharmacotherapy for opioid-use disorder (OUD)-has increased the capacity of healthcare systems to offer treatment, starting this medication is fraught with significant barriers. Standard induction regimens require persons with OUD to taper and discontinue full opioid agonists and experience opioid withdrawal prior to the first dose of buprenorphine. Further, emerging evidence indicates that precipitated withdrawal during induction may impact long-term treatment outcomes. Microinduction is a novel approach that, by harnessing buprenorphine's unique pharmacological profile, may allow circumventing the needed for prolonged opioid tapers, and reduce the risk of precipitated withdrawal-holding promise to enhance treatment access. In this review, we examine the pharmacological basis for microinduction and appraise the evidence of this approach to improve clinical outcomes among persons with OUD. First, we highlight the potential dose-dependent effects of buprenorphine on two key neuroadaptations at the mu-opioid receptor (MOR)-resensitization and upregulation. We then focus on how microinduction may reverse these chronic MOR neuroadaptations, allowing the maintenance of an adequate opioid tone, and thereby potentially circumventing opioid withdrawal. Second, we describe the clinical evidence available, derived from observational reports and open-label studies, examining the potential efficacy of microinduction. Despite significant heterogeneity-exemplified by variable buprenorphine formulations, daily doses, and schedules of administration-these data provide preliminary support for the feasibility of microinduction. Finally, we provide new mechanistic, methodological, and clinical insights to guide future translational research, as well as randomized, placebo-controlled clinical trials in this compelling agenda of pharmacotherapy development.

Threshold dose for intravenous nicotine self-administration in young adult non-dependent smokers.

RATIONALE: Reducing nicotine content of inhaled tobacco products may prevent nicotine addiction, but the threshold for nicotine reinforcement has not been systematically evaluated in controlled human laboratory studies. OBJECTIVES: The current study uses a novel double-blind placebo-controlled intravenous (IV) nicotine self-administration (NSA) model to determine threshold for subjective effects of nicotine and nicotine reinforcement using a forced choice self-administration procedure. METHODS: Young adults (n = 34) had 5 laboratory sessions after overnight nicotine abstinence. In each session, participants sampled and rated the subjective effects of an IV dose of nicotine (0.0125, 0.025, 0.05, 0.1, or 0.2 mg nicotine/70 kg bodyweight) versus saline (placebo), then were given a total of 10 opportunities to self-administer either the IV dose of nicotine or placebo. RESULTS: Mixed effect models revealed a significant effect of nicotine dose for positive (i.e., "stimulatory" and "pleasurable"; p < .0001) effects, but not "aversive" effects during sampling period. Post hoc comparisons showed that higher doses (i.e., 0.1 and 0.2 mg) were associated with greater stimulatory, pleasurable, and physiological effects than placebo and lower doses. Mixed effect models revealed that only the highest dose (i.e., 0.2 mg) was consistently preferred over placebo. Sex differences were generally weak (p = .03-.05). CONCLUSIONS: Using our IV nicotine NSA model, the threshold for detecting positive effects of nicotine in young adult smokers is about 0.1 mg, but a higher dose of nicotine, 0.2 mg, is required to produce a consistent nicotine reinforcement. Regarding the regulatory impact, our findings further support the value of nicotine reinforcement threshold as a tobacco regulatory target.

The effects of inhaled flavors on intravenous nicotine.

Menthol is the only available flavor in combusted tobacco cigarettes; however, e-cigarettes are available in thousands of flavors. Research on flavors and rewarding properties of nicotine is limited. The present study sought to examine the acute rewarding effects of flavors inhaled from an e-cigarette, in combination with intravenous (IV) nicotine among cigarette smokers. In the present study, 24 menthol-preferring young adult (aged 18 to 30) cigarette smokers were tested under 3 different e-cigarette flavor conditions (menthol, green apple, or menthol + green apple) in a within-subject cross-over design. During each test session, each participant received 3 IV infusions (saline, 0.25 mg/70 kg nicotine, 0.5 mg/70 kg nicotine) administered 1 hr apart. The main outcome measures assessed cardiovascular, subjective, and cognitive domains. Compared with green apple or green apple + menthol, menthol produced higher ratings of "cooling" (ps < 0.01). Craving was rated higher following administration of green apple and the combined menthol + apple flavor compared to menthol alone (ps < 0.05). As expected, IV-nicotine dose-dependently increased the ratings of subjective liking/disliking and peak heart rate, improved cognitive performance, and reduced smoking urges (all ps < 0.05). These subjective, cognitive, and physiological effects of nicotine were not affected by any flavor condition. The present findings did not support an interaction between IV-nicotine dose and inhaled flavor for acute effects of nicotine. Green apple flavor, alone or in combination with menthol, could result in higher craving or insufficiently alleviate craving, relative to menthol flavor alone. Additional research is warranted to examine extended exposure to inhaled flavors on the rewarding and addictive effects of nicotine. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Buprenorphine treatment for opioid use disorder: recent progress.

Introduction: Opioid use disorder (OUD) has risen globally and is exerting an enormous toll on public health in many countries, particularly in the United States (US). Buprenorphine (BUP) has become one of the mainstays of pharmacological treatment for OUD and newer delivery methods have been developed to improve its effectiveness in treatment. Areas covered: We provide a review of BUP products available for OUD, with a focus on the newer long-acting formulations. A literature search was conducted using PubMed, Google Scholar, and ClinicalTrials.gov to find randomized clinical trials of long-acting BUP products. Four randomized clinical trials were found: two with BUP implant and two with subcutaneous injectable BUP. Expert opinion: In these clinical trials, new BUP formulations were found to be non-inferior to sublingual (SL) BUP and more effective than placebo in reducing opioid use. Longer-acting formulations can improve flexibility in dosing but superiority over existing SL BUP with regards to outcomes needs to be ascertained. There is a need for more comparative studies between longer-acting BUP formulations and currently available SL BUP. Future studies should also include other clinically meaningful outcomes such as quality of life measures, long-term remission rates, and cost-effectiveness.

Hyperprolactinemia associated with psychotropics--a review.

INTRODUCTION: Different classes of psychotropics can cause hyperprolactinemia to varying degrees. Among antipsychotics, typical agents and risperidone are the most frequent and significant offenders. In this review we discuss the pathophysiology, offending medications, assessment and management of hyperprolactinemia. METHODS: We did a literature review between 1976 and 2008 using PubMed, MEDLINE, PsychINFO and Cochrane database. Search terms used were prolactin, hyperprolactinemia, psychotropics, antipsychotics, typical antipsychotics, atypical antipsychotics, antidepressants and SSRIs. RESULTS: Prolactin elevation is more common with antipsychotics than with other classes of drugs. Typical antipsychotics are more prone to cause hyperprolactinemia than atypical agents. Management options include discontinuation of offending medication, switching to another psychotropic, supplementing concurrent hormonal deficiencies and adding a dopamine agonist or aripiprazole. CONCLUSION: Clinicians need to be alert about the potential for hyperprolactinemia and its manifestations with these medications. Prolactin levels need to be monitored and other causes of hyperprolactinemia ruled out in suspected cases.