Opioid challenge evaluation of blockade by extended-release naltrexone in opioid-abusing adults: dose-effects and time-course.
ABSTRACT Oral naltrexone's effectiveness as an opioid antagonist has been limited due to poor patient adherence. A long-acting naltrexone formulation may be beneficial. This study evaluated the effects of extended-release injectable naltrexone (XR-NTX), targeted for a one-month duration of action, in blocking opioid agonist challenge effects in humans.
Outpatient non-dependent opioid abusers (N=27) were randomly assigned to a single double-blind IM administration of 75, 150, or 300 mg XR-NTX. To assess the extent of opioid blockade, hydromorphone challenges (0, 3, 4.5, 6 mg IM in ascending order at 1-h intervals [up to 13.5 mg total]) were given at pretreatment baseline and on days 7, 14, 21, 28, 42, and 56. Opioid blockade was assessed via (1) tolerability of the ascending hydromorphone doses; (2) visual analog scale (VAS) ratings of subjective opioid effects and (3) pupil diameter. Effects on the VAS and pupils were assessed via the slope of the time-action function over ascending hydromorphone doses, with zero slope indicating complete blockade.
Blockade of the VAS "any drug effect" response to 3 mg hydromorphone was complete for 14, 21, and 28 days, respectively, for the XR-NTX doses of 75, 150, and 300 mg. Subjective effects were more readily blocked than was pupil constriction. Higher hydromorphone doses produced only modest increases in agonist effects. With the 300 mg XR-NTX dose the slope of VAS responses remained at or near zero for one month even with maximal cumulative hydromorphone dosing.
These data quantify the month-long opioid blockade underlying XR-NTX's efficacy in opioid dependence treatment.
SourceAvailable from: Richard J Bodnar[Show abstract] [Hide abstract]
ABSTRACT: This paper is the thirty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2012 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).Peptides 10/2013; 50. DOI:10.1016/j.peptides.2013.10.001 · 2.61 Impact Factor
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ABSTRACT: Adherence to oral naltrexone has been poor and can be improved somewhat with behavioral therapy. We compared behavioral naltrexone therapy (BNT) to compliance enhancement (CE) and tested efficacy of single-dose injection naltrexone (XR-NTX; 384mg) with behavioral therapies at further improving adherence to oral naltrexone. A 24-week, randomized, placebo-controlled trial (n=125) compared four treatment conditions following inpatient detoxification and oral naltrexone induction: (1) BNT+XR-NTX; (2) BNT+placebo injection; (3) CE+XR-NTX; and (4) CE+placebo injection. All participants were maintained on oral naltrexone throughout the trial. Primary outcome was retention in treatment. Of 89 randomized participants, 78.7% (70/89) completed 4 weeks, 58.2% (54/89) completed 8 weeks, 47.2% (42/89) completed 12 weeks, and 25.8% (23/89) completed 24 weeks. A Cox proportional hazards regression modeled time to dropout as a function of treatment condition, baseline opioid dependence severity (bags per day of heroin use), and their interaction. Interaction of conditions by baseline severity was significant (X3(2)=9.19, p=0.027). For low-severity patients (≤6 bags/day), retention was highest in the BNT-XR-NTX group (60% at 6 months), as hypothesized. For high-severity (>6 bags/day) patients, BNT-XR-NTX did not perform as well, due to high early attrition. For low-severity heroin users, single-dose XR-NTX improved long-term treatment retention when combined with behavioral therapy. In higher-severity opioid-dependent patients, XR-NTX was less helpful, perhaps because, combined with oral naltrexone, it produced higher blood levels and more withdrawal discomfort. When cost considerations recommend oral naltrexone following XR-NTX, the latter should be phased in slowly. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.Drug and Alcohol Dependence 12/2014; 147. DOI:10.1016/j.drugalcdep.2014.11.028 · 3.28 Impact Factor
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ABSTRACT: Naltrexone is effective in treating opioid dependence by blocking µ, κ and δ opiate receptors. Naltrexone is mainly metabolized to an active metabolite 6β-naltrexol by dihydrodiol dehydrogenase enzymes. Concomitant opioids will not be effective while patients are taking this antagonist. This was a retrospective analysis of urinary excretion data collected from patients being treated with pain between November 2011 and May 2012. Naltrexone, 6β-naltrexol and concomitant opiate concentrations were measured by liquid chromatography-tandem mass spectrometry. Interpatient variability was calculated from first-visit specimens, and intrapatient variability was calculated from patients with two or more visits. Relationships of the metabolic ratio (MR; 6β-naltrexol/naltrexone) with age, gender and urinary pH were also explored. From 88 first-visit patient specimens, the median MR was 3.28 (range 0.73-17.42). The MR was higher in women than men (5.00 vs. 3.14, P< 0.05). The MR showed no association based on age and urinary pH. Eighteen of 88 patients taking oral naltrexone tested positive for concomitant opiate use. Urinary MRs of 6β-naltrexol/naltrexone were highly variable, which may contribute to variability in efficacy, toxicity and patient willingness to take naltrexone as directed. Twenty percent of patients tested positive for opiates and naltrexone, thus showing the importance of monitoring patients taking naltrexone.Journal of analytical toxicology 03/2014; 38(4). DOI:10.1093/jat/bku019 · 2.63 Impact Factor