Nalfurafine hydrochloride, a selective κ opioid receptor agonist, has no reinforcing effect on intravenous self-administration in rhesus monkeys.

Nalfurafine hydrochloride [(E)-N-[17-(cyclopropylmethyl)-4,5α-epoxy-3,14-dihydroxymorphinan-6ß-yl]-3-(furan-3-yl)-N-methylprop-2-enamide monohydrochloride; nalfurafine] is used in Japan as an antipruritic for the treatment of intractable pruritus in patients undergoing hemodialysis or with chronic liver disease. It is a potent and selective agonist at the κ opioid receptor, but also has weak and partial agonist activity at µ opioid receptors. Opioids, especially those acting at µ receptors, carry a risk of abuse. This is an important factor in the consideration of therapeutic risk vs. benefit in clinical use and the potential for misuse as a public health problem. It is therefore necessary to carefully evaluate the reinforcing effects of nalfurafine. To this end, we investigated intravenous self-administration of nalfurafine in rhesus monkeys. The number of self-administration of nalfurafine at doses of 0.0625, 0.125 and 0.25 µg/kg/infusion was not higher than that of saline in rhesus monkeys that frequently self-administered pentazocine (0.25 mg/kg/infusion). These results indicate that nalfurafine has no reinforcing effect in rhesus monkeys in the intravenous self-administration paradigm.

One year long-term study on abuse liability of nalfurafine in hemodialysis patients.

Nalfurafine (nalfurafine hydrochloride, TRK-820, Remitch®) was launched as an anti-pruritic for uremic pruritus in hemodialysis patients in Japan in 2009. Since the drug is an opioid that mainly binds to κ-receptors and possesses κ-agonistic pharmacological properties and also binds partially, but very weakly, to µ-receptors, the abuse liability of the drug was assessed by using questionnaires in patients enrolled in a clinical trial evaluating the efficacy and safety of the drug. The clinical trial was conducted for up to 52 weeks in patients subjected to regular hemodialysis. End-stage renal disease (ESRD) patients with uremic pruritus (n = 146) were administered nalfurafine 5 µg intravenously after each hemodialysis session. 81 ESRD patients without uremic pruritus served as non-treatment controls. All pruritus patients answered the 3 questionnaires of "the Addiction Research Centre Inventory (ARCI)", "modified Short Opiate Withdrawal Scale (SOWS)", which provides a range of signs and symptoms of opiate withdrawal, and Severity of Dependence Scale (SDS), which measures the dependence potential of the drug. The control patients were tested with the ARCI and modified SOWS questionnaires. There were no significant differences between the nalfurafine group and control group in the ARCI and modified SOWS scales. Thus, no evidence of abuse liability was indicated in the results. Also, no significant differences in the blood pressure, respiratory rate, body temperature and pupil diameter were shown between the two groups.

Efficacy and safety of a novel ĸ-agonist for managing intractable pruritus in dialysis patients.

BACKGROUND: Our previous placebo-controlled, prospective, double-blind study demonstrated that a new opioid ĸ-receptor agonist, nalfurafine hydrochloride, effectively reduced treatment-resistant pruritus in 337 hemodialysis patients. Thus, we designed this study to evaluate prospectively the efficacy, safety, addiction liability, and pharmacokinetics of nalfurafine given orally for 1 year. METHODS: This open-label study examined the effects and adverse drug reactions (ADRs) of 52-week oral administration of nalfurafine hydrochloride (5 µg/day) in 211 hemodialysis patients with a treatment-resistant itch. RESULTS: Of 211 patients, 145 completed the study as scheduled. The mean pruritus value assessed by the visual analogue scale was 75.2 mm during the pre-observation period, which decreased significantly to 50.9 and 30.9 mm in week 2 and 52, respectively, indicating a long-lasting efficacy. ADRs occurred in 103 patients (48.8%). Frequent ADRs were insomnia (sleep disturbance, 19.4%), constipation (7.1%) and increased blood prolactin (3.3%), similar to previous reports. Regarding addiction liability, it appeared unlikely that nalfurafine hydrochloride was abused. After the start of treatment, plasma drug levels reached a steady state in week 2 with no apparent tendency of systemic accumulation. CONCLUSIONS: Nalfurafine hydrochloride, orally administered at 5 µg/day for 52 weeks to hemodialysis patients, produced a long-term suppression of pruritus without significant safety problems.

Psychosocial withdrawal characteristics of nicotine compared with alcohol and caffeine.

The purpose of the present study was to observe the psychosocial characteristics of withdrawal from cigarette smoking in comparison with those from caffeine (CAF) and alcoholic (ALC) beverage withdrawal. Twenty-seven healthy volunteers at a medial level of dependence on both cigarettes (nicotine, NCT) and either CAF or ALC, as judged by the DSM-IV-TR criteria for substance dependence, participated in this study. The participants were required to abstain from smoking and either CAF or ALC for 7 days, each one after another, with a 7-day interval. The order of abstinence was counterbalanced among the participants. Psychosocial parameters, including a desire for substances, social activity function, well-being, withdrawal symptoms, and vital signs, were assessed during the withdrawal periods. The study protocol was approved by the Jikei University Review Board. The results indicated that there were no differences in the maximum level of desire for a substance and the influence on social activity function between NCT and other substances during the withdrawal periods. As for withdrawal symptoms, NCT caused a more intensive degree of irritability than CAF or ALC, and a more intensive degree of difficulty concentrating and restlessness than did withdrawal from ALC. However, the subjective well-being questionnaire indicated no differences in these symptoms between NCT and other substances. The present results suggest that there are no significant differences in psychosocial manifestations regarding the difficulty in abstaining from NCT, CAF, and ALC.

Effects of ifenprodil on the discriminative stimulus effects of cocaine in rhesus monkeys.

Ifenprodil is a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist which prefers NR2B-containing NMDA receptors to NR2A-containing NMDA receptors. It has been reported that ifenprodil suppresses morphine-induced place preference in mice. In this study, the effects of ifenprodil on the discriminative stimulus effects of cocaine were examined in rhesus monkeys. Five monkeys were trained to discriminate cocaine at 0.25 or 0.5 mg/kg im from saline using a standard two-lever drug-discrimination paradigm under a fixed-ratio schedule of food reinforcement. A single dose of cocaine (0.06-0.5 mg/kg) produced a dose-dependent increase in cocaine-appropriate response, and training doses produced 100% cocaine-lever response in each monkey. Pretreatment with ifenprodil (1 or 2 mg/kg, i.v.) blocked the cocaine-appropriate response when low doses of cocaine were used. The results suggest that NR2B-containing NMDA receptor-mediated mechanisms modulate the discriminative stimulus effects of cocaine in rhesus monkeys.

[Clinical features of nicotine dependence].

Nicotine dependence is characterized by weak dependence potential and less ability to produce psychotoxicity and social disturbance. A two-compartment model consisting of "dependence" and "dependence syndrome" was used to clarify clinical features of nicotine dependence. "Dependence" was defined by drug liking. "Dependence syndrome" was defined by a compulsion to take a drug, and drug-induced pathological symptoms (withdrawal syndrome and acute disorders) and social disturbance. Nicotine produced a mild or the least degree of drug liking and withdrawal syndrome, without any significant social disturbance, or acute disorders. Thus, nicotine dependence differed from other forms of drug dependence in that nicotine was not associated with "dependence syndrome". This review also introduced other current topics of nicotine dependence. First, adolescence is regarded as a risk factor for the development of nicotine dependence, whereas the involvement of gender difference (female) in this respect is controversial. Secondly, many smokers feel difficulties in quitting smoking in spite of the weak dependence potential of nicotine, which is known as the "nicotine paradox". Several working hypotheses have been presented to explain this phenomenon. For example, nicotine has relatively strong conditioning effects and/or dependence liability compared with other drugs of abuse. However, further studies should be carried out to clarify clinical characteristics of the "nicotine paradox".

Clinical features of nicotine dependence compared with those of alcohol, methamphetamine, and inhalant dependence.

A new clinical evaluation form was developed to compare the clinical features of nicotine dependence with those associated with other abused drugs. A new scoring system for clinical evaluation was developed. The form consisted of five scoring items: subjective effects, liking (of drug), withdrawal syndrome, acute psychic and physical disorders, and social disturbance. A preliminary clinical investigation was performed to test the validity of the evaluation form. Study subjects were those showing dependence on nicotine (cigarette smoking, n = 40), alcohol (n = 39), methamphetamine (n = 31), and inhalants (n = 30), who fulfilled the DSM-IV-TR criteria for drug dependence disregarding the state of "a maladaptive pattern of substance use, leading to clinically significant impairment or distress," and gave written informed consent for participation in the study. Nicotine caused a mild or the least degree of subjective effects, liking, and psychic and physical withdrawal symptoms, without any significant social disturbance or acute disorders. With alcohol, liking, withdrawal syndrome, and acute physical disorders were prominent. Methamphetamine produced the most serious acute psychic disorders, with intensive acute physical disorders and psychic withdrawal symptoms. Inhalants were characterized by an intensive degree of acute psychic disorders. As for social disturbance, alcohol, methamphetamine, and inhalants showed more significant influence than nicotine. Our study findings revealed that the clinical features of drug dependence could be evaluated by using the new clinical evaluation form. Further study is required to clarify the clinical features of nicotine dependence compared with those of other drugs of dependence.

[Studies on clinical characteristics of nicotine dependence using a two compartment model of drug dependence].

The purpose of the present study was to develop a new clinical evaluation form to compare the clinical characteristics of nicotine dependence with those associated with other drugs of abuse, using a two-compartment model consisting of "drug dependence" and "dependence syndrome". The evaluation form consisted of five scoring items: subjective effects, drug liking, withdrawal syndrome, acute psychic and acute physical disorders, and social disturbance. "Drug dependence" was defined by positive scores on the "drug liking" item. "Dependence syndrome" was defined by positive scores on drug-induced pathological symptoms (withdrawal syndrome, and acute psychic and physical disorders) and social disturbance. The subjects were dependent on nicotine (cigarette smoking) (n = 114), alcohol (n = 101), methamphetamine (n = 90), inhalants (n = 63), and benzodiazepines (n = 39). All subjects met the DSM-IV-TR criteria for drug dependence. Nicotine produced a mild or the least degree of drug liking and withdrawal syndrome, without any significant social disturbance, or acute disorders. The other four drugs produced more intensive degrees of withdrawal syndrome and acute psychic and physical symptoms, with more significant social disturbance than nicotine. The present study indicated that nicotine dependence differed from other forms of drug dependence in that nicotine was not associated with "dependence syndrome".

[Studies on clinical features of nicotine dependence in comparison with those of alcohol and methamphetamine dependence using a two compartment model of drug dependence].

The purpose of the present study was to develop a new clinical evaluation form to compare the clinical features of nicotine dependence with those associated with alcohol and methamphetamine dependence, using a two compartment model consisting of "drug dependence" and "dependence syndrome". The evaluation form consisted of six scoring items: subjective effects, tolerance, drug liking, social disturbance, withdrawal syndrome, and acute psychic and acute physical disorders. "Drug dependence" was defined by positive scores on the "drug liking" item. "Dependence syndrome" was defined by positive scores on drug-induced pathological symptoms (withdrawal syndrome, and acute psychic and physical disorders) and social disturbance. The subjects were dependent on nicotine (n = 68), alcohol (n = 62), or methamphetamine (n = 55). All subjects met DSM-IV diagnostic criteria for drug dependence. Nicotine produced a mild degree of drug liking and psychic withdrawal symptoms, but did not cause significant physical withdrawal symptoms, acute psychic or physical disorders or social disturbance. Alcohol and methamphetamine produced a moderate degree of drug liking and significant levels of withdrawal syndrome, acute disorders and social disturbance. Thus, in the present study, nicotine dependence differed from other forms of drug dependence in that nicotine was not associated with "dependence syndrome".

Brain regions mediating the discriminative stimulus effects of nicotine in rats.

The involvement of cerebral regions in the discriminative stimulus (DS) effects of nicotine was studied using rats. Substitution tests with nicotine administered into the medial prefrontal cortex, nucleus accumbens, and ventral tegmental area, all of which are located on the mesolimbocortical dopaminergic neurons, and into the dorsal hippocampus and medial habenular nucleus, which possess high densities of nicotinic cholinergic receptors, were conducted in rats trained to discriminate nicotine (0.5 mg/kg s.c.) from saline solution in a two-lever, food-reinforced, operant task. Nicotine administered into the medial prefrontal cortex substituted for nicotine (0.5 mg/kg s.c.), whereas nicotine administered into the nucleus accumbens and ventral tegmental area partially substituted for sc injected nicotine. However, nicotine administered into the dorsal hippocampus and medial habenular nucleus did not substitute for sc injected nicotine. These results suggest that the medial prefrontal cortex is primarily involved in the DS effects of nicotine, whereas the nucleus accumbens and ventral tegmental area are partially involved.