Evaluation of the effects of lofexidine and clonidine on naloxone-precipitated withdrawal in opioid-dependent humans

The cell-permeant antioxidant D-thiol ester D-cysteine ethyl ester overcomes physical dependence to morphine in male Sprague Dawley rats

The ability of morphine to decrease cysteine transport into neurons by inhibition of excitatory amino acid transporter 3 (EAA3) may be a key molecular mechanism underlying the acquisition of physical and psychological dependence to morphine. This study examined whether co-administration of the cell-penetrant antioxidant D-thiol ester, D-cysteine ethyl ester (D-CYSee), with morphine, would diminish the development of physical dependence to morphine in male Sprague Dawley rats. Systemic administration of the opioid receptor antagonist, naloxone (NLX), elicited pronounced withdrawal signs (e.g., wet-dog shakes, jumps, rears, circling) in rats that received a subcutaneous depot of morphine (150 mg/kg, SC) for 36 h and continuous intravenous infusion of vehicle (20 μL/h, IV). The NLX-precipitated withdrawal signs were reduced in rats that received an infusion of D-CYSee, but not D-cysteine, (both at 20.8 μmol/kg/h, IV) for the full 36 h. NLX elicited pronounced withdrawal signs in rats treated for 48 h with morphine (150 mg/kg, SC), plus continuous infusion of vehicle (20 μL/h, IV) that began at the 36 h timepoint of morphine treatment. The NLX-precipitated withdrawal signs were reduced in rats that received a 12 h infusion of D-CYSee, but not D-cysteine, (both at 20.8 μmol/kg/h, IV) that began at the 36 h timepoint of morphine treatment. These findings suggest that D-CYSee may attenuate the development of physical dependence to morphine and reverse established dependence to the opioid in male Sprague Dawley rats. Alternatively, D-CYSee may simply suppress the processes responsible for NLX-precipitated withdrawal. Nonetheless, D-CYSee and analogues may be novel therapeutics for the treatment of opioid use disorders.

Lipophilic analogues of D-cysteine prevent and reverse physical dependence to fentanyl in male rats

We examined whether co-injections of the cell-permeant D-cysteine analogues, D-cysteine ethyl ester (D-CYSee) and D-cysteine ethyl amide (D-CYSea), prevent acquisition of physical dependence induced by twice-daily injections of fentanyl, and reverse acquired dependence to these injections in freely-moving male Sprague Dawley rats. Injection of the opioid receptor antagonist, naloxone HCl (NLX, 1.5 mg/kg, IV), elicited a series of withdrawal phenomena that included cardiorespiratory and behavioral responses, and falls in body weight and body temperature, in rats that received 5 or 10 injections of fentanyl (125 μg/kg, IV), and the same number of vehicle co-injections. Regarding the development of physical dependence, the NLX-precipitated withdrawal phenomena were markedly reduced in fentanyl-injected rats that had received co-injections of D-CYSee (250 μmol/kg, IV) or D-CYSea (100 μmol/kg, IV), but not D-cysteine (250 μmol/kg, IV). Regarding reversal of established dependence to fentanyl, the NLX-precipitated withdrawal phenomena in rats that had received 10 injections of fentanyl (125 μg/kg, IV) was markedly reduced in rats that received co-injections of D-CYSee (250 μmol/kg, IV) or D-CYSea (100 μmol/kg, IV), but not D-cysteine (250 μmol/kg, IV), starting with injection 6 of fentanyl. This study provides evidence that co-injections of D-CYSee and D-CYSea prevent the acquisition of physical dependence, and reverse acquired dependence to fentanyl in male rats. The lack of effect of D-cysteine suggests that the enhanced cell-penetrability of D-CYSee and D-CYSea into cells, particularly within the brain, is key to their ability to interact with intracellular signaling events involved in acquisition to physical dependence to fentanyl.

L-cysteine ethyl ester prevents and reverses acquired physical dependence on morphine in male Sprague Dawley rats

The molecular mechanisms underlying the acquisition of addiction/dependence on morphine may result from the ability of the opioid to diminish the transport of L-cysteine into neurons via inhibition of excitatory amino acid transporter 3 (EAA3). The objective of this study was to determine whether the co-administration of the cell-penetrant L-thiol ester, L-cysteine ethyl ester (L-CYSee), would reduce physical dependence on morphine in male Sprague Dawley rats. Injection of the opioid-receptor antagonist, naloxone HCl (NLX; 1.5 mg/kg, IP), elicited pronounced withdrawal phenomena in rats which received a subcutaneous depot of morphine (150 mg/kg) for 36 h and were receiving a continuous infusion of saline (20 μL/h, IV) via osmotic minipumps for the same 36 h period. The withdrawal phenomena included wet-dog shakes, jumping, rearing, fore-paw licking, 360° circling, writhing, apneas, cardiovascular (pressor and tachycardia) responses, hypothermia, and body weight loss. NLX elicited substantially reduced withdrawal syndrome in rats that received an infusion of L-CYSee (20.8 μmol/kg/h, IV) for 36 h. NLX precipitated a marked withdrawal syndrome in rats that had received subcutaneous depots of morphine (150 mg/kg) for 48 h) and a co-infusion of vehicle. However, the NLX-precipitated withdrawal signs were markedly reduced in morphine (150 mg/kg for 48 h)-treated rats that began receiving an infusion of L-CYSee (20.8 μmol/kg/h, IV) at 36 h. In similar studies to those described previously, neither L-cysteine nor L-serine ethyl ester (both at 20.8 μmol/kg/h, IV) mimicked the effects of L-CYSee. This study demonstrates that 1) L-CYSee attenuates the development of physical dependence on morphine in male rats and 2) prior administration of L-CYSee reverses morphine dependence, most likely by intracellular actions within the brain. The lack of the effect of L-serine ethyl ester (oxygen atom instead of sulfur atom) strongly implicates thiol biochemistry in the efficacy of L-CYSee. Accordingly, L-CYSee and analogs may be a novel class of therapeutics that ameliorate the development of physical dependence on opioids in humans.

Open label trial of lofexidine-assisted non-opioid induction onto naltrexone extended-release injection for opioid use disorder

Background: Opioid use disorder (OUD) continues to be major public health problem in the US and innovative medication strategies are needed. The extended-release injectable formulation of naltrexone (ER-NTX), an opioid receptor antagonist, is an effective treatment for OUD, but the need for an opioid-free period during the induction phase of treatment is a barrier to treatment success, particularly in the outpatient setting. Lofexidine, an alpha-2-adrenergic agonist, is an effective treatment for opioid withdrawal.Objectives: To evaluate the feasibility, safety, and tolerability of lofexidine for facilitating induction onto ER-NTX in the management of OUD.Methods: In an open-label, uncontrolled, 10-week outpatient clinical trial, 20 adults (four women) with OUD were treated with a fixed-flexible dosing strategy (maximum 0.54 mg 4×/daily) of lofexidine for up to 10 days to manage opioid withdrawal prior to receiving ER-NTX. The COVID-19 pandemic resulted in a modification of the study methods after enrolling 10 participants who attended all visits in person. The second group of 10 participants attended most induction period visits remotely.Results: Overall, 10 of the 20 participants (50%) achieved the primary outcome by receiving the first ER-NTX injection. Rates of induction success did not differ by the presence of fentanyl or remote visit attendance, although the small sample size provided limited statistical power. Six out of 20 participants (30%) initiated on lofexidine required dose adjustments. There were no study-related serious adverse events.Conclusions: This study provides preliminary evidence supporting the feasibility of inducting individuals with OUD onto ER-NTX using lofexidine.

Mechanism of opioid addiction and its intervention therapy: Focusing on the reward circuitry and mu-opioid receptor

Opioid abuse and addiction have become a global pandemic, posing tremendous health and social burdens. The rewarding effects and the occurrence of withdrawal symptoms are the two mainstays of opioid addiction. Mu-opioid receptors (MORs), a member of opioid receptors, play important roles in opioid addiction, mediating both the rewarding effects of opioids and opioid withdrawal syndrome (OWS). The underlying mechanism of MOR-mediated opioid rewarding effects and withdrawal syndrome is of vital importance to understand the nature of opioid addiction and also provides theoretical basis for targeting MORs to treat drug addiction. In this review, we first briefly introduce the basic concepts of MORs, including their structure, distribution in the nervous system, endogenous ligands, and functional characteristics. We focused on the brain circuitry and molecular mechanism of MORs-mediated opioid reward and withdrawal. The neuroanatomical and functional elements of the neural circuitry of the reward system underlying opioid addiction were thoroughly discussed, and the roles of MOR within the reward circuitry were also elaborated. Furthermore, we interrogated the roles of MORs in OWS, along with the structural basis and molecular adaptions of MORs-mediated withdrawal syndrome. Finally, current treatment strategies for opioid addiction targeting MORs were also presented.

Improving Translational Research Outcomes for Opioid Use Disorder Treatments

Purpose of Review

Pharmacotherapies are the most effective means of reducing the harms associated with opioid use disorder (OUD). Translational research seeking to develop novel medications to treat OUD has been challenging due to the complex etiology of addiction. Preclinical outcome measures are often behavioral, and it is difficult, if not impossible, to fully mirror the various emotional and cognitive processes that motivate opioid use in humans. The goal of the current narrative review was to summarize the translational progression of three potential medications for OUD, which had varying levels of success.

Recent Findings

Memantine, lorcaserin, and lofexidine all showed promise in preclinical studies; however, only lofexidine was able to consistently replicate these findings in human subjects, and receive FDA approval. It was the authors' objective to use this review to identify areas of needed improvement in translational research for OUD.

Summary

Preclinical studies vary significantly in their ability to forecast effectiveness in clinical trials. Among the various preclinical models, suppression of opioid self-administration appears to have the best predictive validity. As they model a mostly physiological phenomenon, preclinical assessments of opioid withdrawal also appear to have high predictive validity. In our review of the literature, the authors noted numerous examples of clinical trials that were underpowered, lack precision, and proper outcomes. Better-validated preclinical targets and improved design of proof-of-concept human studies should allow investigators to more efficiently develop and test medications for OUD.

Opioid use disorder

Opioid use disorder (OUD) is a chronic relapsing disorder that, whilst initially driven by activation of brain reward neurocircuits, increasingly engages anti-reward neurocircuits that drive adverse emotional states and relapse. However, successful recovery is possible with appropriate treatment, although with a persisting propensity to relapse. The individual and public health burdens of OUD are immense; 26.8 million people were estimated to be living with OUD globally in 2016, with >100,000 opioid overdose deaths annually, including >47,000 in the USA in 2017. Well-conducted trials have demonstrated that long-term opioid agonist therapy with methadone and buprenorphine have great efficacy for OUD treatment and can save lives. New forms of the opioid receptor antagonist naltrexone are also being studied. Some frequently used approaches have less scientifically robust evidence but are nevertheless considered important, including community preventive strategies, harm reduction interventions to reduce adverse sequelae from ongoing use and mutual aid groups. Other commonly used approaches, such as detoxification alone, lack scientific evidence. Delivery of effective prevention and treatment responses is often complicated by coexisting comorbidities and inadequate support, as well as by conflicting public and political opinions. Science has a crucial role to play in informing public attitudes and developing fuller evidence to understand OUD and its associated harms, as well as in obtaining the evidence today that will improve the prevention and treatment interventions of tomorrow.

Lofexidine versus clonidine for mitigation of opioid withdrawal symptoms: A systematic review

OBJECTIVES

The U.S. Food and Drug Administration recently approved lofexidine, an α-2-adrenergic agonist, as the first non-opioid medication for mitigation of opioid withdrawal symptoms. Clonidine, an α-2-adrenergic agonist, historically was used off-label for this indication. This review aimed to evaluate the effectiveness of lofexidine versus clonidine for mitigation of opioid withdrawal symptoms and to discuss the current role of lofexidine in the management of patients at risk of experiencing opioid withdrawal.

DATA SOURCES

MEDLINE/PubMed, EBSCO, and CENTRAL were searched using the terms "lofexidine," "clonidine," and "opioid withdrawal."

STUDY SELECTION

The literature search included English-language studies involving administration and prescription of lofexidine and clonidine for the management of opioid withdrawal symptoms in adults. Data sources were searched to include articles published between October 1993 and May 2019.

DATA EXTRACTION

Three independent reviewers analyzed the title and abstract of studies to identify studies involving comparisons of lofexidine with clonidine for mitigation of opioid withdrawal symptoms. Reviewers were initially blinded to the individual determinations. Results were then unblinded and discussed among reviewers.

RESULTS

Of the 110 citations screened, 5 articles were included. One study demonstrated a statistically significant reduction in opioid withdrawal symptom severity with lofexidine compared with clonidine, whereas the other 4 studies showed no significant difference. Three studies reported the completion of opioid detoxification treatment, with no significant differences seen. In 1 study that compared lofexidine with placebo, lofexidine caused significant hypotension, bradycardia, and pupillary constriction. Three studies showed significant adverse effects of hypotension and symptoms of feeling unwell with clonidine compared with lofexidine.

CONCLUSION

Lofexidine appears equivalent in efficacy to clonidine, with fewer adverse effects, and it may have a limited role in the management of opioid withdrawal symptoms. However, cost, detoxification venue, and value of other preferred treatment modalities may affect the comparative efficacy of lofexidine to other agents.

Clinical Efficacy and Safety Profile of Lofexidine Hydrochloride in Treating Opioid Withdrawal Symptoms: A Review of Literature

Opioid use disorder (OUD) is a rapidly growing challenge worldwide and is characterized by an increase in dependence on opioids up to a point that a person loses control over the drug use. Multiple drugs are approved for its treatment, including methadone, buprenorphine, and diazepam. Although not approved, clonidine is also used for the treatment of OUD. On May 16, 2018, the United States Food and Drug Administration (FDA) approved a new drug lofexidine hydrochloride for the treatment of opioid withdrawal symptoms. Lofexidine is a centrally acting alpha two receptor agonist. It reduces the neurochemical surge by inhibiting the conversion of adenosine triphosphate (ATP) into cyclic adenosine monophosphate (cAMP) which in turn decrease the sympathetic outflow. This results in the improvement of withdrawal symptoms. When compared with methadone and buprenorphine, it is equally effective in controlling withdrawal symptoms. Its efficacy is also similar to clonidine with a better side effects profile. The adverse effects of lofexidine include bradycardia, hypotension, orthostasis, somnolence, sedation, dry mouth, and rebound elevations in blood pressure and prolongation of QT interval. Lofexidine is contraindicated in patients who are on beta-blockers and angiotensin converting enzyme inhibitors (ACE inhibitors). In our review, we have discussed the clinical efficacy and safety profile of lofexidine in treating opioid withdrawal symptoms and its comparison to other available treatment options.

Pharmacological therapies for management of opium withdrawal

BACKGROUND

Pharmacologic therapies for management of heroin withdrawal have been studied and reviewed widely. Opium dependence is generally associated with less severe dependence and milder withdrawal symptoms than heroin. The evidence on withdrawal management of heroin might therefore not be exactly applicable for opium.

OBJECTIVES

To assess the effectiveness and safety of various pharmacologic therapies for the management of the acute phase of opium withdrawal.

SEARCH METHODS

We searched the following sources up to September 2017: CENTRAL, MEDLINE, Embase, CINAHL, PsycINFO, regional and national databases (IMEMR, Iranmedex, and IranPsych), main electronic sources of ongoing trials, and reference lists of all relevant papers. In addition, we contacted known investigators to obtain missing data or incomplete trials.

SELECTION CRITERIA

Controlled clinical trials and randomised controlled trials on pharmacological therapies, compared with no intervention, placebo, other pharmacologic treatments, different doses of the same drug, and psychosocial intervention, to manage acute withdrawal from opium in a maximum duration of 30 days.

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included 13 trials involving 1096 participants. No pooled analysis was possible. Studies were carried out in three countries, Iran, India, and Thailand, in outpatient and inpatient settings. The quality of the evidence was generally very low.When the mean of withdrawal symptoms was provided for several days, we mainly focused on day 3. The reason for this was that the highest severity of opium withdrawal is in the second to fourth day.Comparing different pharmacological treatments with each other, clonidine was twice as good as methadone for completion of treatment (risk ratio (RR) 2.01, 95% confidence interval (CI) 1.69 to 2.38; 361 participants, 1 study, low-quality evidence). All the other results showed no differences between the considered drugs: baclofen versus clonidine (RR 1.06, 95% CI 0.63 to 1.80; 66 participants, 1 study, very low-quality evidence); clonidine versus clonidine plus amantadine (RR 1.03, 95% CI 0.86 to 1.24; 69 participants, 1 study); clonidine versus buprenorphine in an inpatient setting (RR 1.04, 95% CI 0.90 to 1.20; 1 study, 35 participants, very low-quality evidence); methadone versus tramadol (RR 0.95, 95% CI 0.65 to 1.37; 1 study, 72 participants, very low-quality evidence); methadone versus methadone plus gabapentin (RR 1.17, 95% CI 0.96 to 1.43; 1 study, 40 participants, low-quality evidence), and tincture of opium versus methadone (1 study, 74 participants, low-quality evidence).Comparing different pharmacological treatments with each other, adding amantadine to clonidine decreased withdrawal scores rated at day 3 (mean difference (MD) -3.56, 95% CI -5.97 to -1.15; 1 study, 60 participants, very low-quality evidence). Comparing clonidine with buprenorphine in an inpatient setting, we found no difference in withdrawal symptoms rated by a physician (MD -1.40, 95% CI -2.93 to 0.13; 1 study, 34 participants, very low-quality evidence), and results in favour of buprenorpine when rated by participants (MD -11.80, 95% CI -15.56 to -8.04). Buprenorphine was superior to clonidine in controlling severe withdrawal symptoms in an outpatient setting (RR 0.35, 95% CI 0.19 to 0.64; 1 study, 76 participants). We found no difference in the comparison of methadone versus tramadol (MD 0.04, 95% CI -2.68 to 2.76; 1 study, 72 participants) and in the comparison of methadone versus methadone plus gabapentin (MD -2.20, 95% CI -6.72 to 2.32; 1 study, 40 participants).Comparing clonidine versus buprenorphine in an outpatient setting, more adverse effects were reported in the clonidine group (1 study, 76 participants). Higher numbers of participants in the clonidine group experienced hypotension at days 5 to 8, headache at days 1 to 8, sedation at days 5 to 8, dizziness and dry mouth at days 1 to 10, and nausea at days 1 to 9. Sweating was reported in a significantly higher number of participants in the buprenorphine group at days 1 to 10. We found no difference between groups for all the other comparisons considering this outcome.Comparing different dosages of the same pharmacological detoxification treatment, a high dose of clonidine (1 to 1.2 mg/day) did not differ from a low dose of clonidine (0.5 to 0.6 mg/day) in completion of treatment in an inpatient setting (RR 1.00, 95% CI 0.84 to 1.19; 1 study, 68 participants), however a higher number of participants with hypotension was reported in the high-dose group (RR 3.25, 95% CI 1.77 to 5.98). Gradual reduction of methadone was associated with more adverse effects than abrupt withdrawal of methadone (RR 2.25, 95% CI 1.02 to 4.94; 1 study, 20 participants, very low-quality evidence).

AUTHORS' CONCLUSIONS

Results did not support using any specific pharmacological approach for the management of opium withdrawal due to generally very low-quality evidence and small or no differences between treatments. However, it seems that opium withdrawal symptoms are significant, especially at days 2 to 4 after discontinuation of opium. All of the assessed medications might be useful in alleviating symptoms. Those who receive clonidine might experience hypotension.

Palonosetron and hydroxyzine pre-treatment reduces the objective signs of experimentally-induced acute opioid withdrawal in humans: a double-blinded, randomized, placebo-controlled crossover study

BACKGROUND

Treatments for reducing opioid withdrawal are limited and prone to problematic side effects. Laboratory studies, clinical observations, and limited human trial data suggest 5-HT3-receptor antagonists and antihistamines may be effective.

OBJECTIVES

This double-blind, crossover, placebo-controlled study employing an acute physical dependence model evaluated whether (i) treatment with a 5-HT3-receptor antagonist (palonosetron) would reduce opioid withdrawal symptoms, and (ii) co-administration of an antihistamine (hydroxyzine) would enhance any treatment effect.

METHODS

At timepoint T = 0, healthy (non-opioid dependent, non-substance abuser) male volunteers (N = 10) were pre-treated with either a) placebo, b) palonosetron IV (0.75 mg), or c) palonosetron IV (0.75 mg) and hydroxyzine PO (100 mg) in a crossover study design. This was followed at T = 30 by intravenous morphine (10 mg/70kg). At T = 165, 10 mg/70kg naloxone IV was given to precipitate opioid withdrawal. The objective opioid withdrawal score (OOWS) and subjective opioid withdrawal score (SOWS) were determined 5 and 15 minutes after naloxone administration (T = 170, 180, respectively). Baseline measurements were recorded at T = -30 and T = -15.

RESULTS

Comparison of average baseline OOWS scores with OOWS scores obtained 15 minutes after naloxone was significant (p = 0.0001). Scores from 15 minutes post-naloxone infusion showed significant differences in OOWS scores between treatment groups: placebo, 3.7 ± 2.4; palonosetron, 1.5 ± 0.97; and palonosetron with hydroxyzine, 0.2 ± 0.1333.

CONCLUSIONS

Pretreatment with palonosetron significantly reduced many signs of experimentally-induced opioid withdrawal. Co-administration with hydroxyzine further reduced opioid withdrawal severity. These results suggest that 5-HT3 receptor antagonists, alone or in combination with an antihistamine, may be useful in the treatment of opioid withdrawal.

Pain Modulation and Autonomic Function: The Effect of Clonidine

OBJECTIVE

The α2-agonist clonidine is an analgesic agent, whose yet uncertain action may involve either increase in pain modulation efficiency, change in autonomic function, and/or decrease in anxiety level. The present study aimed to examine the effect of oral clonidine on pain perception in healthy subjects in order to reveal its mode of action.

DESIGN

Randomized, double-blind, placebo-controlled study.

SUBJECTS

Forty healthy subjects.

METHODS

Subjects received either 0.15 mg oral clonidine or placebo. We measured pain parameters of heat pain thresholds, tonic heat stimulus, mechanical temporal summation, offset analgesia (OA) and conditioned pain modulation (CPM); autonomic parameters of deep breathing ratio and heart rate variability indices obtained before, during, and after tonic heat stimulus; and psychological parameters of anxiety and pain catastrophizing.

RESULTS

Clonidine decreased systolic blood pressure (P = 0.022) and heart rate (P = 0.004) and increased rMSSD (P = 0.020), though no effect was observed on pain perception, pain modulation, and psychological parameters. Autonomic changes were correlated with pain modulation capacity; for OA, the separate slope model was significant (P = 0.008); in the clonidine group, more efficient OA was associated with lower heart rate (r = 0.633, P = 0.005), unlike in the placebo group.

CONCLUSIONS

The change in autonomic function that was related to the increase in pain modulation capacity, and the lack of change in anxiety, suggest a combined modulatory-autonomic mode of analgesic action for clonidine.

Is it prime time for alpha2-adrenocepter agonists in the treatment of withdrawal syndromes?

The need to treat withdrawal syndromes is a common occurrence in outpatient, inpatient ward, and intensive care unit (ICU) settings. A PubMed and Google Scholar search using alpha2-adrenoreceptor agonist (A2AA), specific A2AA agents, withdrawal syndrome and nicotine, and alcohol and opioid withdrawal terms was performed. A2AA agents appear to be able to modulate many of the signs and symptoms of significant withdrawal syndromes but are also capable of significant side effects, which can limit clinical use. Non-opioid oral A2AA agent use for opioid withdrawal has been well established. Pharmacologic combination therapy that utilizes A2AA agents for withdrawal syndromes appears promising but requires further formal testing to better define which other agents, under what condition(s), and at what A2AA doses are needed. The A2AA dexmedetomidine may be useful as an adjunctive agent in treating severe alcohol withdrawal syndromes in the ICU. In general, the current data does not support the routine use of A2AA as the primary or sole agent to treat ethanol/alcohol or nicotine withdrawal syndromes. Specific A2AA agents such as lofexidine has been shown to have a primary role in non-opioid-based treatment of opioid withdrawal syndrome and dexmedetomidine in combination with benzodiazepines has been shown to have potential in the treatment of severe ICU-based alcohol withdrawal syndrome.

Opioid-like effects of the neurokinin 1 antagonist aprepitant in patients maintained on and briefly withdrawn from methadone

BACKGROUND

Although opioid substitution therapy is an effective clinical tool used to manage opioid abuse and dependence, concerns regarding the current FDA-approved medications have lead to a search for efficacious, non-opioid medications. Preclinical data indicate that neurokinin 1 (NK1) receptor activity may modulate opioid effects and withdrawal. This investigation sought to examine the ability of the NK1 antagonist aprepitant to alter the effects of methadone as well as withdrawal symptoms induced by brief methadone discontinuation.

METHODS

This blinded, placebo-controlled, within-subjects study consisted of placebo and aprepitant conditions. Experimental assessments occurred on the first three days (days 1-3: placebo or aprepitant + methadone) and again on days 8-10 (aprepitant or placebo + methadone). Fifteen methadone-maintained patients completed the investigation. Outcome measures were the assessments of opioid withdrawal, as well as subjective measures of opioid-like effects.

RESULTS

Statistical trends indicated that aprepitant may reduce opioid withdrawal symptoms. When an active dose of aprepitant was administered an hour before methadone, participants reported less desire to use methadone. However, ratings of methadone "Liking" also appeared to increase.

CONCLUSIONS

These data tentatively suggest that aprepitant has some ability to alleviate withdrawal following methadone abstinence, but also appears to increase subjective indicators of methadone's abuse liability. Since few of the differences between aprepitant and placebo reached statistical significance, these data should only be viewed as preliminary. Findings from other studies indicate that higher doses of aprepitant may be more clinically effective. Further clinical investigations are needed in order to determine whether aprepitant is useful for alleviating opioid withdrawal.

Differential effects of acute and chronic treatment with the α2-adrenergic agonist, lofexidine, on cocaine self-administration in rhesus monkeys

BACKGROUND

Lofexidine, an α2-adrenergic agonist, is being investigated as a treatment for reducing opioid withdrawal symptoms and blocking stress-induced relapse to cocaine taking. Opioid abusers are often polydrug abusers and cocaine is one frequent drug of choice. However, relatively little is known about lofexidine interactions with cocaine. The present study investigated the effects of acute and chronic treatment with lofexidine in a pre-clinical model of cocaine self-administration.

METHODS

Male rhesus monkeys were trained to respond for food (1g) and cocaine (0.01 mg/kg/injection) under a fixed ratio 30 (FR30) or a second order FR2 (VR16:S) schedule of reinforcement. Systematic observations of behavior were conducted during and after chronic treatment with lofexidine.

RESULTS

Acute treatment with lofexidine (0.1 or 0.32 mg/kg, IM) significantly reduced cocaine self-administration but responding for food was less effected. In contrast, chronic treatment (7-10 days) with lofexidine (0.1-0.32 mg/kg/h, IV) produced a leftward shift in the cocaine self-administration dose-effect curve, but had no effect on food-maintained responding. Lofexidine did not produce any observable side effects during or after treatment.

CONCLUSIONS

Lofexidine potentiated cocaine's reinforcing effects during chronic treatment. These data suggest that it is unlikely to be effective as a cocaine abuse medication and could enhance risk for cocaine abuse in polydrug abusers.

Systems pharmacology identifies drug targets for Stargardt disease-associated retinal degeneration

A systems pharmacological approach that capitalizes on the characterization of intracellular signaling networks can transform our understanding of human diseases and lead to therapy development. Here, we applied this strategy to identify pharmacological targets for the treatment of Stargardt disease, a severe juvenile form of macular degeneration. Diverse GPCRs have previously been implicated in neuronal cell survival, and crosstalk between GPCR signaling pathways represents an unexplored avenue for pharmacological intervention. We focused on this receptor family for potential therapeutic interventions in macular disease. Complete transcriptomes of mouse and human samples were analyzed to assess the expression of GPCRs in the retina. Focusing on adrenergic (AR) and serotonin (5-HT) receptors, we found that adrenoceptor α 2C (Adra2c) and serotonin receptor 2a (Htr2a) were the most highly expressed. Using a mouse model of Stargardt disease, we found that pharmacological interventions that targeted both GPCR signaling pathways and adenylate cyclases (ACs) improved photoreceptor cell survival, preserved photoreceptor function, and attenuated the accumulation of pathological fluorescent deposits in the retina. These findings demonstrate a strategy for the identification of new drug candidates and FDA-approved drugs for the treatment of monogenic and complex diseases.

The combination very low-dose naltrexone-clonidine in the management of opioid withdrawal

BACKGROUND

The management of withdrawal absorbs substantial clinical efforts in opioid dependence (OD). The real challenge lies in improving current pharmacotherapies. Although widely used, clonidine causes problematic adverse effects and does not alleviate important symptoms of opioid withdrawal, alone or in combination with the opioid antagonist naltrexone. Very low-dose naltrexone (VLNTX) has been shown to attenuate withdrawal intensity and noradrenaline release following opioid agonist taper, suggesting a combination with clonidine may result in improved safety and efficacy.

OBJECTIVES

We investigated the effects of a VLNTX-clonidine combination in a secondary analysis of data from a double-blind, randomized opioid detoxification trial.

METHODS

Withdrawal symptoms and treatment completion were compared following VLNTX (.125 or .25 mg/day) and clonidine (.1-.2 mg q6h) in 127 individuals with OD undergoing 6-day methadone inpatient taper at a community program.

RESULTS

VLNTX was more effective than placebo or clonidine in reducing symptoms and signs of withdrawal. The use of VLNTX in combination with clonidine was associated with attenuated subjective withdrawal compared with each medication alone, favoring detoxification completion in comparison with clonidine or naltrexone placebo. VLNTX/clonidine was effective in reducing symptoms that are both undertreated and well controlled with clonidine treatment and was not associated with significant adverse events compared with other treatments.

CONCLUSIONS AND SCIENTIFIC SIGNIFICANCE

Preliminary results elucidate neurobiological mechanisms of OD and support the utility of controlled studies on a novel VLNTX + low-dose clonidine combination for the management of opioid withdrawal.

Alpha2-adrenergic agonists for the management of opioid withdrawal

BACKGROUND

Withdrawal is a necessary step prior to drug-free treatment or as the end point of long-term substitution treatment.

OBJECTIVES

To assess the effectiveness of interventions involving the use of alpha2-adrenergic agonists to manage opioid withdrawal.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 3, 2008), MEDLINE (January 1966-July 2008), EMBASE (January 1985-2008 Week 31), PsycINFO (1967 to 7 August 2008) and reference lists of articles. We also contacted manufacturers in the field.

SELECTION CRITERIA

Controlled trials comparing alpha2-adrenergic agonists with reducing doses of methadone, symptomatic medications or placebo, or comparing different alpha2-adrenergic agonists to modify the signs and symptoms of withdrawal in participants who were opioid dependent.

DATA COLLECTION AND ANALYSIS

One author assessed studies for inclusion and undertook data extraction. Inclusion decisions and the overall process were confirmed by consultation between all authors.

MAIN RESULTS

Twenty-four studies, involving 1631 participants, were included. Twenty-one were randomised controlled trials.Thirteen studies compared a treatment regime based on an alpha2-adrenergic agonist with one based on reducing doses of methadone. Diversity in study design, assessment and reporting of outcomes limited the extent of quantitative analysis.Alpha2-adrenergic agonists are more effective than placebo in ameliorating withdrawal, and despite higher rates of adverse effects, are associated with significantly higher rates of completion of treatment.For the comparison of alpha2-adrenergic agonist regimes with reducing doses of methadone, there were insufficient data for statistical analysis, but withdrawal intensity appears similar to or marginally greater with alpha2-adrenergic agonists, while signs and symptoms of withdrawal occur and resolve earlier. Participants stay in treatment longer with methadone. No significant difference was detected in rates of completion of withdrawal with adrenergic agonists compared to reducing doses of methadone, or clonidine compared to lofexidine. Clonidine is associated with more adverse effects than reducing doses of methadone. Lofexidine does not reduce blood pressure to the same extent as clonidine, but is otherwise similar to clonidine

AUTHORS' CONCLUSIONS

Clonidine and lofexidine are more effective than placebo for the management of withdrawal from heroin or methadone. No significant difference in efficacy was detected for treatment regimes based on clonidine or lofexidine, and those based on reducing doses of methadone over a period of around 10 days but methadone is associated with fewer adverse effects than clonidine, and lofexidine has a better safety profile than clonidine.

Mechanisms of withdrawal-associated increases in heroin self-administration: pharmacologic modulation of heroin vs food choice in heroin-dependent rhesus monkeys

Opioid withdrawal can produce a constellation of physiological and behavioral signs, including an increase in opioid self-administration. Different mechanisms mediate different withdrawal signs, and the present study used pharmacologic tools to assess mechanisms underlying withdrawal-associated increases in opioid reinforcement. Five rhesus monkeys were rendered heroin dependent via daily 21-h heroin self-administration sessions. One hour after each heroin self-administration session, monkeys chose between heroin (0-0.1 mg/kg per injection) and food (1 g pellets) during 2-h choice sessions. Under these conditions, heroin maintained a dose-dependent increase in heroin choice, such that monkeys responded primarily for food when low heroin doses were available (0-0.01 mg/kg per injection) and primarily for heroin when higher heroin doses were available (0.032-0.1 mg/kg per injection). Periods of spontaneous withdrawal were intermittently introduced by omitting one 21-h heroin self-administration session, and test drugs were administered during these withdrawal periods. Untreated withdrawal robustly increased heroin choice during choice sessions. Withdrawal-associated increases in heroin choice were completely suppressed by the mu opioid agonist morphine (0.032-0.32 mg/kg/h, i.v.), but not by the alpha-2 noradrenergic agonist clonidine (0.01-0.1 mg/kg/h, i.v.), the dopamine/norepinephrine releaser amphetamine (0.032-0.1 mg/kg/h, i.v.), or the kappa-opioid antagonist 5'-guanidinonaltrindole (1.0 mg/kg, i.m.). The corticotropin-releasing factor 1 antagonist antalarmin (1.0-10 mg/kg per day, i.m.) produced a morphine-like suppression of withdrawal-associated increases in heroin choice in one of three monkeys. These results suggest that mechanisms of withdrawal-associated increases in the relative reinforcing efficacy of opioid agonists may be different from mechanisms of many other somatic, mood-related, and motivational signs of opioid withdrawal.

Antagonist-precipitated and discontinuation-induced withdrawal in morphine-dependent rhesus monkeys

RATIONALE

Upon discontinuation of chronic opioid treatment, withdrawal typically peaks in 1-3 days and decreases markedly within 1 week; however, persistent physiological changes have been reported long after other signs have waned.

OBJECTIVE

The goal of this study was to compare the discriminative stimulus, directly observable signs, and physiological effects of withdrawal in morphine-treated monkeys.

MATERIALS AND METHODS

Monkeys received 5.6 mg/kg/12 h morphine and discriminated 0.0178 mg/kg naltrexone while responding under a fixed-ratio 5 schedule of stimulus-shock termination. Drug discrimination, behavioral observation, and telemetry were used to monitor the emergence of withdrawal, as well as any persistent changes, following discontinuation of morphine treatment.

RESULTS

Naltrexone dose (0.001-0.032 mg/kg, s.c.) was positively related with indices of withdrawal. In the discrimination study, monkeys responded on the naltrexone lever 1-5 days following discontinuation of treatment; thereafter, they responded exclusively on the saline lever. After discontinuation of morphine, the frequency of observable signs peaked within 2-3 days and most were not significantly increased after 5 days. In contrast, increased heart rate and body temperature persisted for 14 days, returning to values obtained prior to discontinuation by 21 days.

CONCLUSIONS

To the extent that discriminative stimulus effects of withdrawal in nonhumans are predictive of subjective reports of withdrawal in humans, these data indicate that effective treatments for opioid dependence must address not only the short-term subjective components of withdrawal but also, and perhaps more importantly, lingering behavioral and physiological effects that might contribute to relapse long after chronic drug use is discontinued.

Novel medications to treat addictive disorders

Recent discoveries about the effects of drugs of abuse on the brain and the mechanisms of their addictions; new chemical compounds, including immunotherapies; and new actions of available medications are offering many opportunities for the discovery and development of novel medications to treat addictive disorders. Furthermore, advancements in the understanding of the genetic and epigenetic basis of drug addiction and the pharmacogenetics of the safety and/or efficacy of the medications are providing opportunities for more individualized pharmacotherapy approaches. Although multiple medications have been investigated for treating addictions, only a handful have shown acceptable safety and efficacy and are approved by the US Food and Drug Administration. This article reviews the current medications that are medically safe and have shown promising results for treating opioid, cocaine, methamphetamine, and cannabis addictions.

Modest opioid withdrawal suppression efficacy of oral tramadol in humans

RATIONALE

Tramadol is in an unscheduled atypical analgesic with low rates of diversion and abuse and mixed pharmacologic actions, including modest opioid agonist activity.

OBJECTIVES

The purpose of the current study was to characterize the opioid withdrawal suppression efficacy of oral tramadol.

MATERIALS AND METHODS

Residential, opioid-dependent adults (n = 10) were maintained on morphine (15 mg subcutaneously, quad in diem) for approximately 6 weeks. Spontaneous opioid withdrawal was produced by substituting placebo for scheduled morphine doses 17.5 h before experimental sessions that occurred twice weekly. The acute effects of placebo, tramadol (50, 100, 200, and 400 mg orally), naloxone (0.1 and 0.2 mg intramuscularly [IM]), and morphine (15 and 30 mg IM) were tested under double-blind, double-dummy, randomized conditions. Outcomes included observer- and subject-rated measures, physiologic indices, and psychomotor/cognitive task performance.

RESULTS

Naloxone and morphine produced prototypic opioid antagonist and agonist effects, respectively. Tramadol 50 and 100 mg produced effects most similar to placebo. Tramadol 200 and 400 mg initially produced significant dose-related increases in ratings of "bad effects" and "feel sick," followed by evidence of opioid withdrawal suppression. Tramadol did not produce significant increases on measures of positive drug effects nor any clinically significant physiologic changes.

CONCLUSIONS

Tramadol 200 and 400 mg show evidence of opioid withdrawal suppression without significant observer- and subject-rated opioid agonist effects. The profile of action did not suggest a high risk for tramadol abuse in opioid dependent individuals. Tramadol may be a useful medication for treating opioid withdrawal.