Effect of gabapentin-like compounds on development and maintenance of morphine-induced conditioned place preference

Gabapentin and D-cycloserine alone and in combination with naloxone in methadone-maintained humans responding under a naloxone novel-response discrimination procedure

The present study examined the impact of the N-type calcium channel blocker gabapentin (GBP) and the partial glycine agonist D-cycloserine (CYC) to attenuate the behavioral effects of naloxone in opioid-dependent humans responding under a naloxone discrimination procedure. Methadone-maintained participants were trained to distinguish between a low dose of naloxone (0.15 mg/70 kg, i.m.; i.e., drug A) and placebo (i.e. drug B) under an instructed novel-response drug discrimination procedure, in which participants identify the drug condition as 'A', 'B', or 'N' (neither A nor B - 'novel'). Once the discrimination was acquired, doses of CYC (0, 500, and 625 mg) and GBP (0, 100, 200, and 400 mg) each alone and in combination with the training dose of naloxone were tested. GBP alone produced only placebo-appropriate responding and did not significantly alter naloxone discrimination when coadministered with naloxone, though it modestly reduced naloxone-induced visual analog scale ratings of drug 'strength'. CYC alone also produced predominantly placebo-appropriate responding and did not modulate naloxone-appropriate responding, but increased ratings of bad effects and decreased ratings of like placebo relative to naloxone alone at the 500 mg dose. These null findings regarding the modulation of naloxone discrimination highlight the limited efficacy of GBP and CYC in this context, contributing to the understanding of pharmacological interactions with opioid antagonists and their potential implications for opioid withdrawal treatment.

Spinal Cord Stimulation Paradigms and Alleviation of Neuropathic Pain Behavior in Experimental Painful Diabetic Polyneuropathy

OBJECTIVES

Spinal cord stimulation (SCS) is an alternative treatment option for painful diabetic polyneuropathy (PDPN). Differential target multiplexed (DTM)-SCS is proposed to be more effective than conventional (Con)-SCS. Animal studies are essential for understanding SCS mechanisms in PDPN pain relief. Although the Von Frey (VF) test is the gold standard for preclinical pain research, it has limitations. Operant testing using the conditioned place preference (CPP) test provides insights into spontaneous neuropathic pain relief and enhances the translatability of findings. This study aims to 1) use the CPP test to evaluate Con- and DTM-SCS effects on spontaneous neuropathic pain relief in PDPN animals and 2) investigate the correlation between mechanical hypersensitivity alleviation and spontaneous neuropathic pain relief.

MATERIAL AND METHODS

Diabetes was induced through streptozotocin injection in 32 rats; 16 animals developed PDPN and were implanted with a quadripolar lead. Rats were conditioned for Con-SCS (n = 8) or DTM-SCS (n = 7), and a preference score compared with sham was determined. After conditioning, a 30-minute SCS protocol was conducted. Mechanical sensitivity was assessed using VF before, during, and after SCS.

RESULTS

There were no significant chamber preference changes for DTM-SCS (p = 0.3449) or Con-SCS (p = 0.3632). Subgroups of responders and nonresponders were identified with significant increases in preference score for responders for both DTM-SCS (-266.6 to 119.8; p = 0.0238; n = 4) and Con-SCS (-350.7 to 88.46; p = 0.0148; n = 3). No strong correlation between SCS-induced spontaneous neuropathic pain relief and effects on mechanical hypersensitivity in PDPN animals is noted.

CONCLUSIONS

The CPP test is a valuable tool to test the efficacy of the pain-relieving potential of various SCS paradigms in PDPN animals. The results of this study show no differences in spontaneous neuropathic pain relief between DTM- and Con-SCS in PDPN animals. Furthermore, there is no correlation between the effect of SCS in spontaneous pain relief and hind paw mechanical hypersensitivity.

Towards Multitargeted Ligands as Pain Therapeutics: Dual Ligands of the Cavα2δ-1 Subunit of Voltage-Gated Calcium Channel and the μ-Opioid Receptor

The synthesis and pharmacological activity of a new series of dual ligands combining activities towards the α2δ-1 subunit of voltage-gated calcium channels (Cavα2δ-1) and the μ-opioid receptor (MOR) as novel pain therapeutics are reported. A careful exploration of the pharmacophores related to both targets, which in principle had few common characteristics, led to the design of novel compounds exhibiting both activities. The construction of the dual ligands started from published Cavα2δ-1 ligands, onto which MOR ligand pharmacophoric elements were added. This exercise led to new amino-acidic substances with good affinities on both targets as well as good metabolic and physicochemical profiles and low potential for drug-drug interactions. A representative compound, (2S,4S)-4-(4-chloro-3-(((cis)-4-(dimethylamino)-4-phenylcyclohexyl)methyl)-5-fluorophenoxy)pyrrolidine-2-carboxylic acid, displayed promising analgesic activities in several in vivo pain models as well as a reduced side-effect profile in relation to morphine.

Oral self-administration of pregabalin in a mouse model and the resulting drug addiction features

Prescription drug abuse is an issue that is rapidly growing globally. Pregabalin, an anticonvulsant, analgesic, and anxiolytic medication, is effective in the management of multiple neurological disorders; however, there is increasing concern regarding its widespread illicit use. It has been previously reported in mice that pregabalin can induce conditioned place preference. In this current investigation, the potential of pregabalin to elicit free-choice drinking in a mouse model of drug addiction, and its effect on recognition and withdrawal behaviors after forced abstinence, were studied. Twenty-two male BALB/c mice were randomly divided into three groups (n = 7-8/group); control, pregabalin-30, and pregabalin-60. The study had three phases: habituation (days 1-5) with free water access, free-choice drinking (days 6-13) with pregabalin groups receiving one water and one pregabalin bottle, and forced abstinence (days 14-21) with free water access. On day 13, the first open field test was conducted, followed by the Novel Object Recognition Test. On day 21, the second open field test was performed, followed by the Tail Suspension Test and Forced Swimming Test. Pregabalin elicited voluntary drinking in the higher-dose group, concurrently causing a decline in recognition memory performance in the novel object recognition test. Moreover, pregabalin induced withdrawal behavior after a period of forced abstinence in the forced swimming and tail suspension tests. This is the first report to establish an animal model of free-choice pregabalin drinking that may be used for further molecular studies and targeted therapy for pregabalin addiction.

Pharmacological Therapy of Pruritus in Primary Biliary Cholangitis: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

GOALS

We aim to summarize the current management of pruritus in primary biliary cholangitis (PBC) by evaluating the efficacy and safety of pharmacological therapies.

BACKGROUND

Pruritus is a common symptom of PBC, and evidence regarding the most effective antipruritic agents available is lacking. New pharmacotherapy for PBC has shown promising antipruritic effects.

STUDY

We performed a systematic literature review and meta-analysis including all available double-blind, randomized, placebo-controlled clinical trials that evaluated the efficacy of pharmacotherapy for the symptomatic management of pruritus in PBC. Pruritus was assessed as either a change from baseline or a postintervention score.

RESULTS

We included 33 studies and 20 medications. Using the visual analog scale, cholestyramine did not significantly improve pruritus compared with placebo [standardized mean differences (SMD): -0.94, 95% CI: -2.05 to 0.17], whereas rifampin and nalfurafine hydrochloride both significantly improved pruritus (SMD: -3.29, 95% CI: -5.78 to -0.80; n=23 and SMD: -0.58, 95% CI: -1.04 to -0.12). In addition, Bezafibrate and linerixibat significantly improved pruritus (SMD: -1.05, 95% CI: -1.41 to -0.68; n=110 and SMD: -0.31, 95% CI: -0.62 to -0.04, respectively). This effect was also present within the subgroup analysis by pruritus scale, where both bezafibrate and linerixibat significantly improved pruritus compared with placebo (SMD: -1.09, 95% CI: -1.54 to -0.65; P <0.001; visual analog scale; as postintervention score and SMD: -0.31, 95% CI: -0.62 to -0.01; P =0.04; numeric rating scale; as a change from baseline score, respectively).

CONCLUSIONS

Bezafibrate and Linerixibat are potential second-line antipruritic medications for PBC, particularly those with moderate to severe pruritus.

α2δ-1 protein drives opioid-induced conditioned reward and synaptic NMDA receptor hyperactivity in the nucleus accumbens

Glutamate NMDA receptors (NMDARs) in the nucleus accumbens (NAc) are critically involved in drug dependence and reward. α2δ-1 is a newly discovered NMDAR-interacting protein that promotes synaptic trafficking of NMDARs independently of its conventional role as a calcium channel subunit. However, it remains unclear how repeated opioid exposure affects synaptic NMDAR activity and α2δ-1-NMDAR interaction in the NAc. In this study, whole-cell patch-clamp recordings showed that repeated treatment with morphine in mice markedly increased the NMDAR-mediated frequency of miniature excitatory postsynaptic currents (mEPSCs) and amplitude of puff NMDAR currents in medium spiny neurons in the NAc core region. Morphine treatment significantly increased the physical interaction of α2δ-1 with GluN1 and their synaptic trafficking in the NAc. In Cacna2d1 knockout mice, repeated treatment with morphine failed to increase the frequency of mEPSCs and amplitude of puff NMDAR currents in the NAc core. Furthermore, inhibition of α2δ-1 with gabapentin or disruption of the α2δ-1-NMDAR interaction with the α2δ-1 C terminus-interfering peptide blocked the morphine-elevated frequency of mEPSCs and amplitude of puff NMDAR currents in the NAc core. Correspondingly, systemically administered gabapentin, Cacna2d1 ablation, or microinjection of the α2δ-1 C terminus-interfering peptide into the NAc core attenuated morphine-induced conditioned place preference and locomotor sensitization. Our study reveals that repeated opioid exposure strengthens presynaptic and postsynaptic NMDAR activity in the NAc via α2δ-1. The α2δ-1-bound NMDARs in the NAc have a key function in the rewarding effect of opioids and could be targeted for treating opioid use disorder and addiction.

Gabapentin increases the abuse liability of alcohol alone and in combination with oxycodone in participants with co-occurring opioid and alcohol use disorder

BACKGROUND

People who have co-occurring Alcohol Use Disorder (AUD) and Opioid Use Disorder (OUD) carry a higher risk of adverse outcomes, including drug overdose. Early clinical and preclinical studies suggested that gabapentin may be effective in treating both disorders. The present study was designed to assess the effects of gabapentin on the subjective and physiological effects of oxycodone (OXY) and alcohol (ALC), alone and in combination.

METHODS

During an 8-week, inpatient, within-subject, randomized, double-blind, placebo-controlled crossover study, non-treatment seeking participants (N = 13; 12 M/1F; 44.1 ± 3 years of age) with OUD and AUD were maintained on oral morphine (120 mg daily). Under gabapentin (1800 mg/day) and placebo (0 mg/day) maintenance, participants completed nine separate test sessions (three sessions per week) during which they received an oral solution containing 0, 15, or 30 mg/70 kg OXY in combination with 0, 0.5, or 0.75 g/kg ALC. During test sessions, subjective effects and physiological responses were assessed repeatedly on 100-mm visual analog scales (VAS). The primary outcome variable was the VAS rating of drug liking after receiving the drug challenge.

RESULTS

Alcohol alone (but not oxycodone alone) produced dose-related increases in several positive subjective responses, including drug liking. Gabapentin significantly increased drug liking when given in combination with ALC and OXY + ALC (p < 0.05). Gabapentin did not clinically compromise respiration or other vital functions.

CONCLUSIONS

Gabapentin may increase the abuse liability of ALC and OXY + ALC in those with co-occurring OUD and AUD.

Comparative Study of the Neurotoxic Effects of Pregabalin Versus Tramadol in Rats

In Egypt, both pregabalin and tramadol misuse increased in the last decade. Although many studies have confirmed the neurotoxic effects of tramadol, those of pregabalin are understudied. The aim of the study is to evaluate the neurotoxic effects of pregabalin compared with tramadol. Thirty male albino rats were included in this experimental study, and they were randomly allocated into three equal groups: group I (normal saline), group II (tramadol misuse), and group III (pregabalin misuse). All rats received the commenced drugs for 1 month. Open field tests were performed on the day of scarification, and after that, cortical samples were taken for immunohistochemical analysis and quantification of dopamine receptors' gene expression. The drug misuse groups showed a significant decrease in weight gain at the end of the study. Open field testing showed the upper hand of controls regarding all of the tested parameters. Tramadol has a more negative impact on the locomotor parameters compared with pregabalin. Both drugs induced relatively low dopamine-1 receptor (D1Rs) expression to dopamine-2 receptors (D2Rs), mimicking the schizophrenia model. Both tramadol and pregabalin were associated with neurotoxic effects in male albino rats. These effects were less noticed with pregabalin. It is suggested that long-term abuse may end in psychosis.

Consuming illicit opioids during a drug overdose epidemic: Illicit fentanyls, drug discernment, and the radical transformation of the illicit opioid market

BACKGROUND

North America continues to face an opioid overdose epidemic, driven by persistent increases in illicit fentanyls and fluctuations in potency leading to uncertainty for consumers. This qualitative study was conducted to better understand how people who inject drugs (PWID) came to recognize fentanyl as a growing adulterant of heroin and the subsequent sensory discernment strategies they employed to continue injecting. Our main objective was to investigate how observations and knowledge are combined as homegrown techniques for detecting fentanyl and minimizing risk. Secondary objectives were to examine the impact of growing fentanyl adulteration on individual drug use behavior.

METHODS

Between April and May 2019, 28 PWID (18 men, 10 women; average age = 38.43 years, SD = 9.26) were purposely recruited from a needle services program in Greensboro, North Carolina. Study participants were interviewed in-person using a qualitative, semi-structured instrument. Interviews were analyzed with a general inductive approach using NVivo12.

RESULTS

Participants described methods for detecting fentanyl in illicit opioids. Sudden increases in the potency of the 'rush' and sharp decreases in the length of the 'high' were chief indicators along with changes in drug color and texture. Heavy sedation was associated with fentanyl use and histamine-releasing effects characterized as 'pins and needles' were ascribed to injecting fentanyl as a component of the rush. Fentanyl's short high helped explain higher injection frequency and heavy sedation was the leading reason for co-using fentanyl with cocaine/crack or methamphetamine.

CONCLUSION

PWID have the capacity to recognize changes to the illicit opioid supply. Study participants navigated unpredictable fluctuations in the illicit opioid market by employing homegrown discernment techniques, modifying drug use behavior, and co-using non-opioid drugs. Researchers and policymakers should involve PWID as subject matter experts to help modernize harm reduction for the fentanyl age with practical strategies to boost resiliency and save lives.

Stimulation and transient inactivation of ventral tegmental area modify reinstatement of acquisition phase of morphine-induced conditioned place preference in male rats

For processing the development of psychological dependency, opioid reinforcement, and opiate-related associative reward, learning, and memory in the brain, the ventral tegmental area (VTA) is considered the key zone. As the responsible region for the morphine role in conditioned place preference (CPP), this area has an important role. So, the present research was conducted to investigate the effects of different intensities of electrical stimulation on VTA utilizing CPP, with two morphine doses. Reversible inactivation of VTA was performed via bilateral microinjection of Lidocaine into this area with two implanted separate cannulas. Our findings indicated that 5 mg/kg morphine-induced CPP was suppressed by 150 μA VTA electrical stimulation. The results also showed that bilateral Intra-VTA administration of Lidocaine significantly decreased the 5 mg/kg morphine-induced CPP acquisition phase in comparison with their respective sham group, which reversed in the reinstatement test. It should be concluded that these findings are important for the detection of mesolimbic nervous system ties and could help to find new ways to attenuate the rewarding action of morphine.

Opioid Tapering/Detoxification Protocols, A Compendium: Narrative Review

OBJECTIVES

The opioid epidemic has put pressure on clinicians to taper their chronic pain patients (CPPs) from opioids. This has resulted in rapid or forced tapers and opioid discontinuation. Partially responsible is lack of information on how to taper (tapering protocols).The objectives of this narrative review were then the following: compile all the published opioid tapering/detoxification protocols from the pain/drug rehabilitation/psychiatric literature whether for inpatient or outpatient use; organize these into general types; compare the types for advantages/disadvantages for use by a clinician in an outpatient setting; and answer some commonly asked questions relating to opioid tapering.

METHODS

Relevant references were identified by a search strategy utilizing the terms tapering, tapering protocols, detoxification, detoxification protocols, withdrawal, dependence, addiction, and drug rehabilitation. These were explored with the term opioids. Identified abstract were reviewed for any study relating to the objectives of this review. Those studies were then included in this review. As this is a narrative review, no quality ratings of these references were performed.

RESULTS

Of 1,922 abstracts identified by this search strategy, 301 were reviewed in detail for potential inclusion. Of these, 104 were utilized in this review. Nine types of opioid tapering protocols were identified and compared in tabular form. Twenty-two questions in reference to opioid tapering were addressed.

CONCLUSIONS

Based on this review, the protocol utilizing the opioid of current use is the simplest to use as it requires no rotation to another opioid and thereby avoids rotation errors. It also has behavior advantages.

Development and validation of a rapid liquid chromatography/tandem mass spectrometry method to quantitate gabapentin and buprenorphine in human serum

RATIONALE

Gabapentin has shown initial promise as an opioid-sparing medication in pain patients as well as a treatment for opioid withdrawal and liquid chriomatography/tandem mass spectrometry (LC/MS/MS) is often used for clinical monitoring. Despite reports of validated tandem mass spectrometric methods for the determination of gabapentin and buprenorphine, mechanisms for the collision-induced fragmentation have not been adequetely described.

METHODS

A rapid analytical method has been developed to determine gabapentinoid, gabapentin, and the partial opioid agonist, buprenorphine, in 20 μL of human serum using LC/MS/MS with a chromatographic run time of 2 min. A simplified sample cleanup procedure using methanol precipitation of serum proteins/lipids followed by evaporation and reconstitution in mobile phase was demonstrated. Gabapentin and buprenorphine were detected following positive ion electrospray ionization using multiple-reaction monitoring. The internal standard approach was used for quantitation with labeled gabapentin-D10 and buprenorphine-D4 serving as internal standards. Using organic reaction principals and stable isotope labels, collision-induced fragmentation mechanisms for both gabapentin and buprenorphine are proposed. The method was validated according to the FDA Guidance for Industry - Bioanalytical Method Validation.

RESULTS

Accuracy was demonstrated by error values ≤15% for buprenorphine and ≤6% for gabapentin. The inter-day precision was ≤4.88% and 15.59% for gabapentin and buprenorphine and the intra-day precision was ≤5.20% and 11.65% for gabapentin and buprenorphine. The lower limit of quantitation corresponded to 10 ng/mL for gabapentin and 1 ng/mL for buprenorphine in serum. Recoveries were 104 ± 2.55% and 85 ± 2.03% for gabapentin and buprenorphine, respectively.

CONCLUSIONS

Concentrations of gabapentin and buprenorphine were determined for five authentic human serum samples to further validate the utility of the method and applicable to therapeutic drug monitoring beyond its use as a drug screening assay. Furthermore, new mechanisms for the collision-induced dissociation of gabapentin and buprenorphine have been proposed.

Potential Benefits of N-Acetylcysteine in Preventing Pregabalin-Induced Seeking-Like Behavior

Substance-use disorder is globally prevalent and responsible for numerous social and medical problems. Pregabalin (Lyrica), typically used to treat diabetic neuropathy, has recently emerged as a drug of abuse. Drug abuse is associated with several neuronal changes, including the downregulation of glutamate transporters such as glutamate transporter 1 and cystine/glutamate antiporter. We investigated the effects of N-acetylcysteine, a glutamate transporter 1 and xCT upregulator, on pregabalin addiction using a conditioned place preference paradigm. Pregabalin (60 mg/kg) was found to induce conditioned place preference when compared to a vehicle. A 100 mg/kg dose of N-acetylcysteine was found to block pregabalin-seeking behaviors. These results support previous findings showing that glutamate transporters play an important role in pregabalin-induced seeking behaviors. N-acetylcysteine may represent a beneficial agent in preventing the abuse potential of pregabalin.

Current Evidence on Abuse and Misuse of Gabapentinoids

This review summarizes current evidence on the abuse and misuse of the gabapentinoids pregabalin and gabapentin. Pharmacovigilance studies, register-based studies, surveys, clinical toxicology studies, and forensic toxicology studies were identified and scrutinized with the goal to define the problem, identify risk factors, and discuss possible methods to reduce the potential for abuse and misuse. Studies found that gabapentinoids are abused and misused and that individuals with a history of psychiatric disorders or substance use disorder seem to be at high risk. Moreover, some evidence supports the notion that patients with opioid use disorders may be at an increased risk of abusing gabapentinoids. Available evidence also suggests that abuse and misuse are more frequent in users of pregabalin compared with users of gabapentin. Health professionals and prescribers should be aware of the risk for misuse of pregabalin and gabapentin, which eventually could lead to abuse, substance dependence, and intoxications. Prescribing to patients belonging to risk populations such as those with psychiatric disorders or substance use disorder should be avoided if possible and, if prescribed, signs of misuse and abuse should be monitored.

Sex differences in pregabalin-seeking like behavior in a conditioned place preference paradigm

Substance abuse is a chronic, relapsing disorder characterized by compulsive drug use regardless of negative consequences. Incremental increases in pregabalin abuse have been observed in Saudi Arabia and throughout the world. In previous studies, the potential for pregabalin abuse with escalating doses of the drug (30, 60, 90, and 120 mg/kg) were investigated in male mice. Notably, researchers have argued that women may exhibit a greater tendency to consume drugs without a prescription to alleviate stress and depression. Moreover, female subjects are more prone to impulsivity in drug intake or abuse than their male counterparts. Therefore, in the present study, we compared the potential for pregabalin abuse between male and female mice using a conditioned place preference paradigm. Male and female BALB/c mice were divided into four groups based on the pregabalin dose administered (30, 60, 90, or 120 mg/kg, intraperitoneal). Preference scores were then calculated and compared between male and female mice in each dosage group. Interestingly, preference scores were significantly higher in female mice than in male mice at dosages of 30 and 120 mg/kg. These findings indicate that female mice may be more prone to pregabalin abuse and tolerance than male mice. These results might be helpful to the healthcare providers and policymakers to consider these sex differences in choosing therapeutic plans and consider alternatives to the misused prescription medications.

Gabapentinoid Benefit and Risk Stratification: Mechanisms Over Myth

INTRODUCTION

Recent years have seen a dramatic escalation of off-label prescribing for gabapentin and pregabalin (gabapentinoids) owing in part to generic versions of each being released over the past two decades, but also in part as a response to increasing calls for multimodal and non-opioid pain management strategies. In this context, several recent articles have been published alleging widespread misuse, with speculations on the unappreciated addictive potential of the gabapentinoid class of drugs. Reports of a 1% population-level abuse prevalence stem from a single internet survey in the UK, and the vanishingly small adverse event outcomes data do not support such frequency. In this targeted narrative review, we aim to disabuse pain physicians and other clinicians, pharmacists, and policymakers of both the positive and negative myths concerning gabapentinoid medications.

RESULTS

Gabapentinoids inhibit the joint action of voltage-gated calcium channel (VGCC) α2δ subunits in conjunction with the n-methyl-D-aspartate (NMDA) receptor, with subsequent downregulation of VGCC expression and excitatory neurotransmitter release, and possibly synaptogenesis as well, through actions on thrombospondins. These activities reduce the likelihood of central sensitization, which explains in part the efficacy of the gabapentinoids in the management of neuropathic pain. Gabapentinoids also facilitate slow-wave sleep, a relatively rare phenomenon among central nerve system-acting agents, which is also thought to explain some of the therapeutic benefit of the class in conditions such as fibromyalgia. The number needed to treat to see benefit overlaps that of the nonsteroidal anti-inflammatory drugs, but with a considerably improved safety profile. Along these lines, in the context of over 50 million prescriptions per year in the USA alone, the gabapentinoids display remarkably low risk, including risks of misuse, abuse, and dependence. Furthermore, the neurobiology of these agents does not lend plausibility to the allegations, as they have never been shown to elicit dopaminergic activity within the nucleus accumbens, and in addition likely confer a "negative-feedback loop" for habituation and dependence by serving as functional NMDA antagonists, possibly through their actions on thrombospondins. Clinical and epidemiological addictionology studies corroborate the lack of any significant addictive potential of the gabapentinoids, and these drugs are increasingly being used in the treatment of addiction to other substances, with excellent results and no evidence of cross-addiction. However, among individuals with other substance use disorders and, in particular opioid use disorder, there are consistent data showing misuse of gabapentinoids in up to 20% of this population. Although there are allegations of using gabapentinoids to amplify the hedonic effects of opioids, the vast majority of misuse events appear to occur in an attempt to ameliorate opioid withdrawal symptoms. Furthermore, rare but potentially serious respiratory depression may occur, again amplified in the context of opioid or other sedative use. Careful risk:benefit assessment and stratification are warranted when prescription of a gabapentinoid is under consideration, in particular among individuals using opioids.

CONCLUSIONS

Gabapentinoids remain a vital tool in the pain physician's multimodal armamentarium, but these drugs may not be effective in every clinical situation. Individuals with central sensitization and pain associated with slow-wave sleep deficits and potentially persons with comorbid addictions may benefit the most. The gabapentinoids appear to possess no addictive potential on their own, based on laboratory and clinical data, but they may be abused by persons with opioid use disorders; consequently, cautious risk stratification must take place.

Gabapentin-induced drug-seeking-like behavior: a potential role for the dopaminergic system

Drugs of abuse represent a growing public health crisis. Accumulating evidence indicates that gabapentin (GBP), a prescription drug, is prone to misuse, abuse, withdrawal, and dependence. Commonly, drugs of abuse modulate the dopaminergic system to induce addiction. In this study, we used the conditioned place preference (CPP) model to investigate the involvement of the dopamine 1 (D1) receptor on the reward and reinforcement behavior of GBP. Under a CPP paradigm, male BALB/c mice were intraperitoneally injected either saline or 100, 200, or 300 mg/kg of GBP and confined to the injection-paired chamber for 30 min. In the pre-conditioning phase, mice were conditioned for 3 days, and baseline data were collected. In the conditioning phase, mice were given once-daily alternating injections of either GBP or saline for 8 days and subsequently assessed in a post-conditioning test. Injections of 300 mg/kg of GBP significantly increased the time spent in the drug-paired chamber compared to the saline-paired chamber. However, lower doses of GBP (100 and 200 mg/kg) showed no effect. Pre-treatment with SKF-83566, a D1 receptor antagonist, attenuated GBP-induced CPP. Thus, for the first time, we show that GBP can induce CPP through a dopaminergic-dependent mechanism.

Mutually beneficial effects of intensive exercise and GABAergic neural progenitor cell transplants in reducing neuropathic pain and spinal pathology in rats with spinal cord injury

Spinal cord injury (SCI) produces both locomotor deficits and sensory dysfunction that greatly reduce the overall quality of life. Mechanisms underlying chronic pain include increased neuro-inflammation and changes in spinal processing of sensory signals, with reduced inhibitory GABAergic signaling a likely key player. Our previous research demonstrated that spinal transplantation of GABAergic neural progenitor cells (NPCs) reduced neuropathic pain while intensive locomotor training (ILT) could reduce development of pain and partially reverse already established pain behaviors. Therefore, we evaluate the potential mutually beneficial anti-hypersensitivity effects of NPC transplants cells in combination with early or delayed ILT. NPC transplants were done at 4 weeks post-SCI. ILT, using a progressive ramping treadmill protocol, was initiated either 5 days post-SCI (early: pain prevention group) or at 5 weeks post-SCI (delayed: to reverse established pain) in male Sprague Dawley rats. Results showed that either ILT alone or NPCs alone could partially attenuate SCI neuropathic pain behaviors in both prevention and reversal paradigms. However, the combination of ILT with NPC transplants significantly enhanced neuropathic pain reduction on most of the outcome measures including tests for allodynia, hyperalgesia, and ongoing pain. Immunocytochemical and neurochemical analyses showed decreased pro-inflammatory markers and spinal pathology with individual treatments; these measures were further improved by the combination of either early or delayed ILT and GABAergic cellular transplantation. Lumbar dorsal horn GABAergic neuronal and process density were nearly restored to normal levels by the combination treatment. Together, these interventions may provide a less hostile and more supportive environment for promoting functional restoration in the spinal dorsal horn and attenuation of neuropathic pain following SCI. These findings suggest mutually beneficial effects of ILT and NPC transplants for reducing SCI neuropathic pain.

Pregabalin: Potential for Addiction and a Possible Glutamatergic Mechanism

Drug addiction remains a prevalent and fatal disease worldwide that carries significant social and economic impacts. Recent reports suggest illicit pregabalin (Lyrica) use may be increasing among youth, however the addictive potential of pregabalin has not been well established. Drug seeking behavior and chronic drug use are associated with deficits in glutamate clearance and activation of postsynaptic glutamatergic receptors. In the current study, we investigated the abuse potential of pregabalin using conditioned place preference (CPP) paradigm. Different doses of pregabalin (30, 60, 90, and 120 mg/kg) were used to assess the seeking behavior in mice. Glutamate homeostasis is maintained by glutamate transporter type-1 (GLT-1), which plays a vital role in clearing the released glutamate from synapses and drug seeking behavior. Therefore, we investigated the role of glutamate in pregabalin-seeking behavior with ceftriaxone (CEF), a potent GLT-1 upregulator. Mice treated with pregabalin 60 and 90 mg/kg doses demonstrated drug seeking-like behavior, which was significantly blocked by CEF pretreatment. These results suggest that pregabalin-induced CPP was successfully modulated by CEF which could serve as a lead compound for developing treatment for pregabalin abuse.

Lack of correlation between the activity of the mesolimbic dopaminergic system and the rewarding properties of pregabalin in mouse

RATIONALE

Pregabalin is a psychoactive drug indicated in the treatment of epilepsy, neuropathic pain, and generalized anxiety disorders. Pregabalin acts on different neurotransmission systems by inactivating the alpha2-delta subunit of voltage-gated calcium channels. In light of this pharmacological property, the hypothesis has been raised that pregabalin may regulate the mesolimbic dopamine pathway and thereby display a potential for misuse or abuse as recently observed in humans. Although some preclinical data support this possibility, the rewarding properties of gabapentinoid are still a matter for debate.

OBJECTIVE

The aim of this work was to evaluate the rewarding properties of pregabalin and to determine its putative mechanism of action in healthy mice.

RESULTS

Pregabalin alone (60 mg/kg; s.c.) produced a rewarding effect in the conditioned place preference (CPP) test albeit to a lower extent than cocaine (30 mg/kg; s.c.). Interestingly, when assessing locomotor activity in the CPP, the PGB60 group, similarly to the cocaine group, showed an increased locomotor activity. In vivo single unit extracellular recording showed that pregabalin had mixed effects on dopamine (DA) neuronal activity in the ventral tegmental area since it decreased the activity of 50% of neurons and increased 28.5% of them. In contrast, cocaine decreased 75% of VTA DA neuronal activity whereas none of the neurons were activated. Intracerebal microdialysis was then conducted in awake freely mice to determine to what extent such electrophysiological parameters influence the extracellular DA concentrations ([DA]ext) in the nucleus accumbens. Although pregabalin failed to modify this parameter, cocaine produced a robust increase (800%) in [DA]ext.

CONCLUSIONS

Collectively, these electrophysiological and neurochemical experiments suggest that the rewarding properties of pregabalin result from a different mode of action than that observed with cocaine. Further experiments are warranted to determine whether such undesirable effects can be potentiated under pathological conditions such as neuropathic pain, mood disorders, or addiction and to identify the key neurotransmitter system involved.

Gabapentin completely neutralized the acute morphine activation in the rat hypothalamus: a c-Fos study

Aim: The molecular mechanism of gabapentin (GBP)–morphine combinational function and its neuro-anatomical sites of action to prevent, to neutralize morphine side effects and also the enhancement its analgesic effect of morphine is unknown. Methods: Morphine (10 mg/kg), saline, co-injection: GBP (150 mg/kg) with morphine (10 mg/kg) were injected by intraperitoneal injection in rats under deep anaesthesia. C-Fos immunohistochemistry technique was used to locate c-Fos expression in rat hypothalamus. Results: Gabapentin in combination with morphine significantly (p < 0.01) attenuated the acute morphine induced c-Fos immunoreactive neuron in hypothalamus. Conclusion: GBP neutralized the morphine sensitization in rat hypothalamus. GBP might neuromodulate and or antagonize the receptor regulatory machinery of morphine sensitization circuit which might work for drug discovery of morphine abuse.

Calcium channel modulation as a target in chronic pain control

Neuropathic pain remains poorly treated for large numbers of patients, and little progress has been made in developing novel classes of analgesics. To redress this issue, ziconotide (Prialt™) was developed and approved as a first-in-class synthetic version of ω-conotoxin MVIIA, a peptide blocker of Cav 2.2 channels. Unfortunately, the impracticalities of intrathecal delivery, low therapeutic index and severe neurological side effects associated with ziconotide have restricted its use to exceptional circumstances. Ziconotide exhibits no state or use-dependent block of Cav 2.2 channels; activation state-dependent blockers were hypothesized to circumvent the side effects of state-independent blockers by selectively targeting high-frequency firing of nociceptive neurones in chronic pain states, thus alleviating aberrant pain but not affecting normal sensory transduction. Unfortunately, numerous drugs, including state-dependent calcium channel blockers, have displayed efficacy in preclinical models but have subsequently been disappointing in clinical trials. In recent years, it has become more widely acknowledged that trans-aetiological sensory profiles exist amongst chronic pain patients and may indicate similar underlying mechanisms and drug sensitivities. Heterogeneity amongst patients, a reliance on stimulus-evoked endpoints in preclinical studies and a failure to utilize translatable endpoints, all are likely to have contributed to negative clinical trial results. We provide an overview of how electrophysiological and operant-based assays provide insight into sensory and affective aspects of pain in animal models and how these may relate to chronic pain patients in order to improve the bench-to-bedside translation of calcium channel modulators.

LINKED ARTICLES

This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.

Addiction-related interactions of pregabalin with morphine in mice and humans: reinforcing and inhibiting effects

The gabapentinoid pregabalin is a rapid-acting anxiolytic and analgesic, possibly suitable in supervised opioid detoxification. However, clinicians have been cautious in using it because of its unknown addictive risk and rising number of mortalities after pregabalin self-medication in opioid abusers. Here, we studied interactions of pregabalin and morphine on reward functions of the dopamine system in mice and the efficacy of pregabalin on withdrawal in opioid addicts. After the treatment of mice with pregabalin and morphine, we used electrophysiology to study neuroplasticity in midbrain slices, self-administration and conditioned place preference tests to investigate the rewarding potential of pregabalin and naloxone-precipitated morphine withdrawal to evaluate opioid withdrawal symptoms. Further, we ran a pilot single-blind, randomized, controlled trial (34 heroin addicts) to evaluate the efficacy and safety of pregabalin in the treatment of opioid withdrawal syndrome. Pregabalin alone did not induce glutamate receptor neuroplasticity of dopamine neurons in the ventral tegmental area, but pre-treatment with pregabalin suppressed morphine-induced neuroplasticity, hyperlocomotion and morphine self-administration. Pregabalin administration after chronic morphine exposure failed to induce any rewarding effects. Instead, pregabalin suppressed withdrawal symptoms in both morphine-treated mice and opioid addicts and was well tolerated. Intriguingly, pregabalin administration after a low dose of morphine strongly facilitated ventral tegmental area neuroplasticity and led to increased conditioned place preference. Pregabalin appears to have the efficacy to counteract both reinforcing and withdrawal effects of opioids, but it also has a potentiating effect when given to mice with existing opioid levels.

How addictive are gabapentin and pregabalin? A systematic review

In the last ten years, gabapentin and pregabalin have been becoming dispensed broadly and sold on black markets, thereby, exposing millions to potential side-effects. Meanwhile, several pharmacovigilance-databases have warned for potential abuse liabilities and overdose fatalities in association with both gabapentinoids. To evaluate their addiction risk in more detail, we conducted a systematic review on PubMed/Scopus and included 106 studies. We did not find convincing evidence of a vigorous addictive power of gabapentinoids which is primarily suggested from their limited rewarding properties, marginal notes on relapses, and the very few cases with gabapentinoid-related behavioral dependence symptoms (ICD-10) in patients without a prior abuse history (N=4). In support, there was no publication about people who sought treatment for the use of gabapentinoids. Pregabalin appeared to be somewhat more addictive than gabapentin regarding the magnitude of behavioral dependence symptoms, transitions from prescription to self-administration, and the durability of the self-administrations. The principal population at risk for addiction of gabapentinoids consists of patients with other current or past substance use disorders (SUD), mostly opioid and multi-drug users, who preferred pregabalin. Pure overdoses of gabapentinoids appeared to be relative safe but can become lethal (pregabalin > gabapentin) in mixture with other psychoactive drugs, especially opioids again and sedatives. Based upon these results, we compared the addiction risks of gabapentin and pregabalin with those of traditional psychoactive substances and recommend that in patients with a history of SUD, gabapentinoids should be avoided or if indispensable, administered with caution by using a strict therapeutic and prescription monitoring.

Abuse Potential of Pregabalin: A Systematic Review

BACKGROUND

Several case reports and epidemiological studies have raised concern about the abuse potential of pregabalin, the use of which has increased substantially over the last decade. Pregabalin is, in some cases, used for recreational purposes and it has incurred attention among drug abusers for causing euphoric and dissociative effects when taken in doses exceeding normal therapeutic dosages or used by alternative routes of administration, such as nasal insufflation or venous injection. The magnitude of the abuse potential and the mechanism behind it are not fully known.

OBJECTIVE

The aim of this study was to present a systematic review of the data concerning the abuse potential of pregabalin.

METHODS

We performed a systematic literature search and reviewed the preclinical, clinical and epidemiological data on the abuse potential of pregabalin.

RESULTS

We included preclinical (n = 17), clinical (n = 19) and epidemiological (n = 13) studies addressing the abuse potential of pregabalin. We also reviewed case reports (n = 9) concerning abuse of pregabalin. The preclinical studies indicated that pregabalin possesses modulatory effects on the GABA and glutamate systems, leaving room for an abuse potential. Further, clinical studies reported euphoria as a frequent side effect in patients treated with pregabalin. The majority of case reports concerning abuse of pregabalin involved patients with a history of substance abuse and, similarly, epidemiological studies found evidence of abuse, especially among opiate abusers.

CONCLUSIONS

Overall, the available literature suggests an important clinical abuse potential of pregabalin and prescribers should pay attention to signs of abuse, especially in patients with a history of substance abuse.

Randomized, placebo-controlled pilot trial of gabapentin during an outpatient, buprenorphine-assisted detoxification procedure

This pilot study examined the efficacy of the N-type calcium channel blocker gabapentin to improve outcomes during a brief detoxification protocol with buprenorphine. Treatment-seeking opioid-dependent individuals were enrolled in a 5-week, double-blind, placebo-controlled trial examining the effects of gabapentin during a 10-day outpatient detoxification from buprenorphine. Participants were inducted onto buprenorphine sublingual tablets during Week 1, were randomized and inducted onto gabapentin or placebo during Week 2, underwent a 10-day buprenorphine taper during Weeks 3 and 4, and then were tapered off gabapentin/placebo during Week 5. Assessments included thrice-weekly opioid withdrawal scales, vitals, and urine drug screens. Twenty-four individuals (13 male; 17 Caucasian, 3 African American, 4 Latino; mean age 29.7 years) participated in the detoxification portion of the study (gabapentin, n = 11; placebo, n = 13). Baseline characteristics did not differ significantly between groups. Self-reported and observer-rated opioid withdrawal ratings were relatively low and did not differ between groups during the buprenorphine taper. Urine results showed a Drug × Time interaction, such that the probability of opioid-positive urines significantly decreased over time in the gabapentin versus placebo groups during Weeks 3 and 4 (OR = 0.73, p = .004). These results suggest that gabapentin reduces opioid use during a 10-day buprenorphine detoxification procedure.

Pregabalin for opioid-refractory pain in a patient with ankylosing spondylitis

Background. Ankylosing spondylitis (AS) is a systemic inflammatory disease with chronic back pain as the most common presenting symptom. We present a case of a male patient with AS reporting symptoms of severe low back pain, buttock pain, and limited spinal mobility. After chronic treatment with opioids, we administered pregabalin at a dose of 300 mg as an analgesic agent while opioids were discontinued. Findings. Pain symptoms improved progressively, and opioids were gradually discontinued without any withdrawal symptoms reported. Conclusions. Pregabalin is potentially useful in the management of pain in patients with AS while effectively managing the discontinuation of opioid treatment.

Pregabalin- and topiramate-mediated regulation of cognitive and motor impulsivity in DBA/2 mice

BACKGROUND AND PURPOSE

Impulsivity is a core symptom in many neuropsychiatric disorders. The main objective of this study was to evaluate the effects of topiramate and pregabalin on the modulation of different impulsivity dimensions in DBA/2 mice.

EXPERIMENTAL APPROACH

The effects of acute and chronic administration of pregabalin (10, 20 and 40 mg·kg(-1) ) and topiramate (12.5, 25 and 50 mg·kg(-1) ) were evaluated in the light-dark box (LDB), hole board test (HBT) and delayed reinforcement task (DRT). α(2A) -Adrenoceptor, D(2) -receptor and TH gene expression were evaluated by real-time PCR in the prefrontal cortex (PFC), accumbens (ACC) and ventral tegmental area (VTA), respectively.

KEY RESULTS

Acute pregabalin administration showed a clear anxiolytic-like effect (LDB) but did not modify novelty-seeking behaviour (HBT). In contrast, topiramate produced an anxiolytic effect only at the highest dose, whereas it reduced novelty seeking at all doses tested. In the DRT, acute pregabalin had no effect, whereas topiramate only reduced motor impulsivity. Chronically, pregabalin significantly increased motor impulsivity and topiramate diminished cognitive impulsivity. Pregabalin decreased α(2A) -adrenoceptor and D(2) -receptor gene expression in the PFC and ACC, respectively, and increased TH in the VTA. In contrast, chronic administration of topiramate increased α(2A) -adrenoceptor and D(2) -receptor gene expression in the PFC and ACC, respectively, and also increased TH in the VTA.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the usefulness of pregabalin in impulsivity-related disorders is related to its anxiolytic properties, whereas topiramate modulates impulsivity. These differences could be linked to their opposite effects on α(2A) -adrenoceptor and D(2) -receptor gene expression in the PFC and ACC, respectively.

Tolerance and withdrawal from prolonged opioid use in critically ill children

OBJECTIVE

After prolonged opioid exposure, children develop opioid-induced hyperalgesia, tolerance, and withdrawal. Strategies for prevention and management should be based on the mechanisms of opioid tolerance and withdrawal.

PATIENTS AND METHODS

Relevant manuscripts published in the English language were searched in Medline by using search terms "opioid," "opiate," "sedation," "analgesia," "child," "infant-newborn," "tolerance," "dependency," "withdrawal," "analgesic," "receptor," and "individual opioid drugs." Clinical and preclinical studies were reviewed for data synthesis.

RESULTS

Mechanisms of opioid-induced hyperalgesia and tolerance suggest important drug- and patient-related risk factors that lead to tolerance and withdrawal. Opioid tolerance occurs earlier in the younger age groups, develops commonly during critical illness, and results more frequently from prolonged intravenous infusions of short-acting opioids. Treatment options include slowly tapering opioid doses, switching to longer-acting opioids, or specifically treating the symptoms of opioid withdrawal. Novel therapies may also include blocking the mechanisms of opioid tolerance, which would enhance the safety and effectiveness of opioid analgesia.

CONCLUSIONS

Opioid tolerance and withdrawal occur frequently in critically ill children. Novel insights into opioid receptor physiology and cellular biochemical changes will inform scientific approaches for the use of opioid analgesia and the prevention of opioid tolerance and withdrawal.

Discriminative stimulus effects of tiagabine and related GABAergic drugs in rats

RATIONALE

Tiagabine is an anticonvulsant drug which may also have sleep-enhancing properties. It acts by inhibiting reuptake at the gamma-aminobutyric acid (GABA) transporter (GAT-1).

OBJECTIVES

The aim of the study was to determine whether tiagabine acted as a discriminative stimulus and, if so, whether other GABAergic compounds would generalise to it.

MATERIALS AND METHODS

Rats were trained to discriminate tiagabine (30 mg/kg p.o.) from vehicle, and generalisation to drugs that modulate GABA was assessed.

RESULTS

Gaboxadol (5-20 mg/kg p.o.), a selective extrasynaptic GABA A agonist, generalised to tiagabine, although the extent of the generalisation was inconclusive. Indiplon (1 mg/kg p.o.), a benzodiazepine-like hypnotic, also partially generalised to tiagabine, although zolpidem and S-zopiclone did not. Baclofen, a GABA B receptor agonist, and gabapentin, which increases synaptic GABA, did not generalise to tiagabine. (+)-Bicuculline (3 mg/kg i.p.), a GABA A receptor antagonist, blocked the tiagabine cue, but the less brain-penetrant salt form, bicuculline methochloride, had no effect.

CONCLUSIONS

These data suggest that tiagabine generates a discriminative stimulus in rats, and provides a central GABA-mediated cue, but is distinct from the other GABAergic compounds tested.

Pruritus in primary biliary cirrhosis: pathogenesis and therapy

Pruritus is a symptom experienced by patients who have primary biliary cirrhosis. It seems to result from pruritogens that (as a result of cholestasis) accumulate in plasma and other tissues, and which lead to altered neurotrasnmission. Administration of medications that change opioid neurotransmission (ie, opiate antagonists) results in relief of pruritus and its behavioral manifestation, scratching. Through unknown mechanisms, other centrally acting medications, including antidepressants, may have ameliorating effects on the pruritus of cholestasis. Stimulating endogenous detoxification pathways in the liver may also lead to the amelioration of pruritus. The removal of pruritogens through administration of nonabsorbable resins, nasobiliary drainage, biliary diversion, plasmapheresis, and various dialysis procedures is reported to decrease pruritus in liver disease, although the substances that are presumably removed are unknown.

Update: new uses for lithium and anticonvulsants

Anticonvulsants are being used clinically as monotherapy and adjuncts in mental illnesses other than affective disorders. This review focuses on the literature for anticonvulsants and lithium in substance use disorders, anxiety disorders, and schizophrenia. Given the abuse potential and other difficulties with prescribing benzodiazepines for alcohol and benzodiazepine withdrawal, anticonvulsants have been considered as an alternative. Promising therapeutic effects have been demonstrated in many of the anxiety disorders, with the greatest number of trials and positive results in posttraumatic stress disorder. Although anticonvulsant and lithium augmentation for schizophrenia is common in practice and has been studied in double-blind, randomized, controlled trials, the sum of the evidence has been inconclusive.

Measuring reward with the conditioned place preference (CPP) paradigm: update of the last decade

Conditioned place preference (CPP) continues to be one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. This is obvious from a steady year-to-year increase in the number of publications reporting the use this model. Since the compilation of the preceding review in 1998, more than 1000 new studies using place conditioning have been published, and the aim of the present review is to provide an overview of these recent publications. There are a number of trends and developments that are obvious in the literature of the last decade. First, as more and more knockout and transgenic animals become available, place conditioning is increasingly used to assess the motivational effects of drugs or non-drug rewards in genetically modified animals. Second, there is a still small but growing literature on the use of place conditioning to study the motivational aspects of pain, a field of pre-clinical research that has so far received little attention, because of the lack of appropriate animal models. Third, place conditioning continues to be widely used to study tolerance and sensitization to the rewarding effects of drugs induced by pre-treatment regimens. Fourth, extinction/reinstatement procedures in place conditioning are becoming increasingly popular. This interesting approach is thought to model certain aspects of relapse to addictive behavior and has previously almost exclusively been studied in drug self-administration paradigms. It has now also become established in the place conditioning literature and provides an additional and technically easy approach to this important phenomenon. The enormous number of studies to be covered in this review prevented in-depth discussion of many methodological, pharmacological or neurobiological aspects; to a large extent, the presentation of data had to be limited to a short and condensed summary of the most relevant findings.

Carnosine ameliorates morphine-induced conditioned place preference in rats

The histidine-containing dipeptide, carnosine (beta-alanyl-L-histidine), is present in high concentrations in mammalian brain of mammals. There are many theories about its biological functions, such as anti-inflammatory agent, free radical scavenger, and protein glycosylation inhibitor, however, the role of carnosine in morphine addiction is less understood. Therefore, the objectives of this study were to determine the effects of carnosine on the development of morphine-induced conditioned place preference (CPP) and investigate its possible mechanism of action in Sprague-Dawley rats. Intraperitioneal (i.p.) injection of carnosine (200, 500, 1000 mg/kg) significantly inhibited the development of morphine-induced CPP in a dose-dependent manner. Although carnosine had no appreciable effect on the levels of histamine in the ventral tegmental area (VTA), nucleus accumbens (NAc) and prefrontal cortex (PFC), it significantly decreased glutamate level in the VTA, dopamine levels in the NAc and PFC, and DOPAC level in the NAc of morphine-treated rats. These results indicate that carnosine inhibits morphine-induced CPP in rats, and its action may be due to modulation of dopaminergic and glutaminergic activity. The study suggests that carnosine has potential as a new anti-addictive drug.

Gabapentin completely attenuated the acute morphine induced c-Fos expression in the rat striatum

The neuro-anatomical sites and molecular mechanism of action of gabapentin (GBP)-morphine interaction to prevent and reverse morphine side effects as well as enhancement of the analgesic effect of morphine is not known. Therefore, we examined the combined effects of GBP-Morphine on acute morphine induced c-Fos expression in rat striatum. The combined effect of GBP-Morphine was examined by means of c-Fos immunohistochemistry. A single intraperitoneal injection (i.p.) of morphine (10 mg/kg), saline (control), co-injection of GBP (150 mg/kg) with morphine (10 mg/kg) was administered under anaesthesia. Ninety minutes after drugs administration the deeply anesthetized rats were perfused transcardially with 4% paraformaldehyde. Serial 40 mum thick sections of brain were cut and processed by immunohistochemistry to locate and quantify the sites and number of neurons with c-Fos immunoreactivity. Detection of c-Fos protein was performed using the peroxidase-antiperoxidase (PAP) detection protocol. Our present study demonstrated that, administration of GBP (150 mg/kg, i.p.) in combination with morphine (10 mg/kg, i.p.) significantly (p < 0.01) attenuated the acute morphine (10 mg/kg, i.p.) induced c-Fos expression in the rat striatum. Present results showed that GBP-morphine combination action prevented the acute morphine induced c-Fos expression in rat striatum. Moreover, this study provides first evidence of neuro-anatomical site and that GBP neutralized the morphine induced activation of rat striatum.

Gabapentin in patients with the pruritus of cholestasis: a double-blind, randomized, placebo-controlled trial

Pruritus is defined as the second order of nociception, the first being pain; thus, there is a rationale to study gabapentin, a drug that increases the threshold to experience nociception. The aim of this double-blind, randomized, placebo-controlled trial was to study the effect of gabapentin on the perception of pruritus and its behavioral manifestation, scratching, in cholestasis. The participants were 16 women with chronic liver disease and chronic pruritus. Hourly scratching activity (HSA) was continuously recorded for up to 48 hours at baseline and on treatment for at least 4 weeks in an inpatient setting. The perception of pruritus was assessed by interviews and by a visual analog score (VAS) of pruritus recorded every hour while patients were awake. Patients were randomized to the study drug (gabapentin or placebo) at a starting dose of 300 mg orally per day in divided doses to a maximum of 2,400 mg or until relief from pruritus. Gabapentin was associated with an increase in mean HSA, in contrast to the placebo, which was associated with a decrease. The mean VAS decreased significantly among those taking the placebo and in some patients on gabapentin. In conclusion, gabapentin did not provide a significant therapeutic advantage over the placebo; in fact, it was associated with an increase in the perception of pruritus and in HSA in some patients.

Analgesia and sedation during mechanical ventilation in neonates

BACKGROUND

Endotracheal intubation and mechanical ventilation are major components of routine intensive care for very low birth weight newborns and sick full-term newborns. These procedures are associated with physiologic, biochemical, and clinical responses indicating pain and stress in the newborn. Most neonates receive some form of analgesia and sedation during mechanical ventilation, although there are marked variations in clinical practice. Clinical guidelines for pharmacologic analgesia and sedation in newborns based on robust scientific data are lacking, as are measures of clinical efficacy.

OBJECTIVE

This article represents a preliminary attempt to develop a scientific rationale for analgesia sedation in mechanically ventilated newborns based on a systematic analysis of published clinical trials.

METHODS

The current literature was reviewed with regard to the use of opioids (fentanyl, morphine, diamorphine), sedative-hypnotics (midazolam), nonsteroidal anti-inflammatory drugs (ibuprofen, indomethacin), and acetaminophen in ventilated neonates. Original meta-analyses were conducted that collated the data from randomized clinical comparisons of morphine or fentanyl with placebo, or morphine with fentanyl.

RESULTS

The results of randomized trials comparing fentanyl, morphine, or midazolam with placebo, and fentanyl with morphine were inconclusive because of small sample sizes. Meta-analyses of the randomized controlled trials indicated that morphine and fentanyl can reduce behavioral and physiologic measures of pain and stress in mechanically ventilated preterm neonates but may prolong the duration of ventilation or produce other adverse effects. Randomized trials of midazolam compared with placebo reported significant adverse effects (P < 0.05) and no apparent clinical benefit; the findings of a meta-analysis suggest that there are insufficient data to justify use of IV midazolam for sedation in ventilated neonates.

CONCLUSIONS

Despite ongoing research in this area, huge gaps in our knowledge remain. Well-designed and adequately powered clinical trials are needed to establish the safety, efficacy, and short- and long-term outcomes of analgesia and sedation in the mechanically ventilated newborn.

Mechanisms of the antinociceptive action of gabapentin

Gabapentin, a gamma-aminobutyric acid (GABA) analogue anticonvulsant, is also an effective analgesic agent in neuropathic and inflammatory, but not acute, pain systemically and intrathecally. Other clinical indications such as anxiety, bipolar disorder, and hot flashes have also been proposed. Since gabapentin was developed, several hypotheses had been proposed for its action mechanisms. They include selectively activating the heterodimeric GABA(B) receptors consisting of GABA(B1a) and GABA(B2) subunits, selectively enhancing the NMDA current at GABAergic interneurons, or blocking AMPA-receptor-mediated transmission in the spinal cord, binding to the L-alpha-amino acid transporter, activating ATP-sensitive K(+) channels, activating hyperpolarization-activated cation channels, and modulating Ca(2+) current by selectively binding to the specific binding site of [(3)H]gabapentin, the alpha(2)delta subunit of voltage-dependent Ca(2+) channels. Different mechanisms might be involved in different therapeutic actions of gabapentin. In this review, we summarized the recent progress in the findings proposed for the antinociceptive action mechanisms of gabapentin and suggest that the alpha(2)delta subunit of spinal N-type Ca(2+) channels is very likely the analgesic action target of gabapentin.

Improving opioid effectiveness: from ideas to evidence

Opioid effectiveness can be improved by individualizing dosing, route of administration and the drug. Particularly in the treatment of chronic non-cancer pain, careful patient selection is essential. The current review concentrates on new ideas about improving opioid effectiveness by increasing efficacy or reducing adverse effects by combining other drugs that modulate opioid receptor mediated effects. These pharmacological "oipioid adjuvants" include e.g. alpha(2)-adrenergic agonists, non-steroidal anti-flammatory analgesics, NMDA-receptor antagonists, CCK-antagonists, gabapentinoids and NK-1 receptor antagonists. The theoretical background and the clinical evidence of these combinations will be discussed.

Add-on gabapentin in the treatment of opiate withdrawal

Gabapentin is an antiepileptic drug shown to be effective in the treatment of pain disorders and appears to be useful as well for several psychiatric disorders, including bipolar disorder, anxiety disorders, alcohol withdrawal and cocaine dependence. Gabapentin, at a dose of 600 mg three times a day, was evaluated as an add-on medication to a standard detoxification regime in seven heroin dependent individuals undergoing outpatient opiate withdrawal treatment. All seven patients successfully completed opiate detoxification and commenced opiate antagonist treatment with naltrexone on day five of withdrawal treatment, as scheduled. No adverse event was noted. Gabapentin appeared to lead a reduction in symptomatic medication and an overall beneficial effect on symptoms of heroin withdrawal.

Reinforcing versus anticonvulsant drugs: effects on intracranial self-stimulation rate-frequency M50 indices

Drugs of abuse, such as amphetamine and morphine, produce reward-related shifts on intracranial self-stimulation (ICSS) thresholds. The facilitatory effects on ICSS thresholds of drugs that act through the GABAergic system, however, are reported to be attributed to their antiseizure and anticonvulsant effects, rather than their reinforcing effects. Using a rate-frequency ICSS paradigm, we examined the effects of amphetamine (a reinforcing drug of abuse that acts via the catecholaminergic system), pentobarbital (a GABA(A) receptor agonist and reinforcing barbiturate with anticonvulsant properties), and gabapentin (a nonspecific GABAergic agonist and anticonvulsant with low abuse potential) on ICSS M(50) indices. All three doses of amphetamine (0.5, 1.0, and 2.0 mg/kg) and pentobarbital (2.5, 5.0, and 10.0 mg/kg) significantly lowered rate-frequency M(50) values. Gabapentin, on the other hand, significantly raised rate-frequency M(50) values, albeit only at the highest dose administered (30 mg/kg). Our results indicate that shifts in ICSS M(50) values produced by pentobarbital are associated with the reinforcing, not the anticonvulsant, effect of pentobarbital. These results are consistent with the view that there is a common system underlying the reinforcing effects of drugs and ICSS reinforcement, and suggest that the reinforcing and anticonvulsant effects of GABA agonists are dissociable.

Beta-phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids and compounds derived from them, including further products of oxidation, condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2001 to June 2002 is reviewed, with 581 references cited.

Pregabalin: a new anxiolytic

Pregabalin (S-[+]-3-isobutylgaba) was designed as a lipophilic GABA (gamma-aminobutyric acid) analogue substituted at the 3'-position in order to facilitate diffusion across the blood-brain barrier. It was originally developed as an anticonvulsant agent, however it has been shown to be effective in the treatment of several disorders including hyperalgesia and behavioural disorders. Although its exact mode of action remains unclear, pregabalin interacts with the same binding site and has a similar pharmacological profile as its predecessor, gabapentin (1-[aminomethyl] cyclohexane acetic acid). Its main site of action appears to be on the alpha(2)delta subunit of voltage-dependent calcium channels, widely distributed throughout the peripheral and central nervous system. Pregabalin appears to produce an inhibitory modulation of neuronal excitability. In healthy volunteers, it is rapidly absorbed with peak blood concentrations within 1 h and it has a bioavailability of approximately 90%. In preclinical trials of anticonvulsant activity, pregabalin is three to ten times more potent than gabapentin. It is well-tolerated and associated with dose-dependent adverse effects (ataxia, dizziness, headache and somnolence) that are mild-to-moderate and usually transient. There are no known pharmacokinetic drug-drug interactions reported to date. Preliminary animal and human studies showed beneficial effects in both ethological and conflict models of anxiety, as well as having some sleep-modulating properties. In Phase II and III trials, pregabalin shows promising anxiolytic action when compared to placebo in generalised anxiety disorder, social phobia and panic disorder.