Dyskinesias occur in response to saline and naltrexone alone after priming with combination of dopaminergic agents and naltrexone in the MPTP parkinsonian monkeys

Storage of motor memory involves the basal ganglia and more precisely the striatum, which receives afferents from all regions of the cerebral cortex. In Parkinsonian (MPTP) monkeys, we observed an increase in the dyskinetic response to dopaminergic agents when combined with opioid antagonists (naloxone or naltrexone) while morphine, attenuated the dyskinetic response. An interesting phenomenon observed after several acute co-administrations of naltrexone with dopaminergic agents was the manifestation of dyskinesias even after the injection of saline or naltrexone alone. However, this phenomenon was not observed when morphine was used in the same conditions. These unexpected observations concerning the acquisition of dyskinesias with saline or naltrexone alone, reported for the first time, might suggest the implication of a learning phenomenon in the induction of levodopa-induced dyskinesias.

Adding Ultralow-Dose Naltrexone to Oxycodone Enhances and Prolongs Analgesia: A Randomized, Controlled Trial of Oxytrex

Oxytrex is a novel drug that combines oxycodone with ultralow-dose naltrexone, an opioid antagonist. Ultralow-dose opioid antagonists have been demonstrated to enhance and prolong opiate analgesia and alleviate opioid tolerance and withdrawal in rodents. This 3-week, Phase II clinical trial assessed safety and analgesic efficacy of Oxytrex in patients with moderate to severe pain from osteoarthritis. Patients with a pain score > or =5 received placebo, oxycodone 4 times a day (qid), Oxytrex qid, or Oxytrex twice a day (bid). All active treatment groups received the same total daily dose and dose escalation of oxycodone starting at 10 and ending at 40 mg/day. Importantly, the Oxytrex bid group received a lower daily dose of naltrexone than Oxytrex qid (0.002 vs 0.004 mg/day). Oxytrex bid produced a 39% reduction in pain intensity, which was significantly greater than that of placebo (P < .001), oxycodone qid (P = .006), and Oxytrex qid (P = .003). Oxytrex bid was also superior to placebo in quality of analgesia (P = .002), duration of pain control each day (P = .05), patients' global assessments (P = .04), and the Western Ontario and MacMaster Universities Osteoarthritis Index total score (P = .03). The incidence of side effects was comparable between active treatments. In this Phase II dose-ranging study, Oxytrex bid demonstrated greater pain relief with a more convenient dosing schedule compared to oxycodone qid.

PERSPECTIVE

Preclinical data have shown ultralow-dose opioid antagonists to enhance and prolong opioid analgesia while reducing analgesic tolerance and physical dependence. Recent molecular pharmacology data show a mechanism of action to be the prevention of aberrant G protein coupling by opioid receptors that underlies opioid tolerance and dependence.

Reinstatement of cocaine-seeking behavior in rats is attenuated following repeated treatment with the opioid receptor antagonist naltrexone

In the present study we show that the endogenous opioid systems play a modulating role in cocaine-induced reinstatement of drug-seeking behavior in rats. We investigated the effect of blockade of opioid receptors on reinstatement of cocaine-seeking behavior by cocaine priming. Drug-naive rats were allowed to initiate self-administration behavior of cocaine (30 and 60 mug per infusion, i.v.) for 5 consecutive daily sessions, and after a 5-day extinction period during which the rats did not receive cocaine, a test for cocaine-induced (1 mg/kg, i.v.) reinstatement followed. The effect of cocaine priming was tested on days 1, 3, and 5 after extinction, while on days 2 and 4 the animals received saline priming. Before each daily reinstatement test, different groups of animals received an injection with the opioid receptor antagonist naltrexone (3 mg/kg, s.c.) or with placebo. We observed that cocaine readily reinstated extinguished responding in the rats, and that this reinstatement responding did not change over the consecutive reinstatement tests. Pretreatment with naltrexone progressively attenuates the cocaine-induced reinstatement, with a significant reduction on days 3 and 5 of reinstatement testing. Discriminative lever-pressing (active versus inactive lever) during reinstatement phase, however, remains present in animals treated with naltrexone. This implies that repeated opioid receptor blockade progressively attenuates cocaine-induced drug-seeking behavior in abstained animals, but this cannot simply be attributed to extinction of cocaine-seeking behavior.

Efficacy and tolerability of long-acting injectable naltrexone for alcohol dependence: a randomized controlled trial

CONTEXT

Alcohol dependence is a common disorder associated with significant morbidity and mortality. Naltrexone, an opioid antagonist, has been shown to be effective for treatment of alcohol dependence. However, adherence to daily oral pharmacotherapy can be problematic, and clinical acceptance and utility of oral naltrexone have been limited.

OBJECTIVE

To determine efficacy and tolerability of a long-acting intramuscular formulation of naltrexone for treatment of alcohol-dependent patients.

DESIGN, SETTING, AND PARTICIPANTS

A 6-month, randomized, double-blind, placebo-controlled trial conducted between February 2002 and September 2003 at 24 US public hospitals, private and Veterans Administration clinics, and tertiary care medical centers. Of the 899 individuals screened, 627 who were diagnosed as being actively drinking alcohol-dependent adults were randomized to receive treatment and 624 received at least 1 injection.

INTERVENTION

An intramuscular injection of 380 mg of long-acting naltrexone (n = 205) or 190 mg of long-acting naltrexone (n = 210) or a matching volume of placebo (n = 209) each administered monthly and combined with 12 sessions of low-intensity psychosocial intervention.

MAIN OUTCOME MEASURE

The event rate of heavy drinking days in the intent-to-treat population.

RESULTS

Compared with placebo, 380 mg of long-acting naltrexone resulted in a 25% decrease in the event rate of heavy drinking days (P = .02) [corrected] and 190 mg of naltrexone resulted in a 17% decrease (P = .07). Sex and pretreatment abstinence each showed significant interaction with the medication group on treatment outcome, with men and those with lead-in abstinence both exhibiting greater treatment effects. Discontinuation due to adverse events occurred in 14.1% in the 380-mg and 6.7% in the 190-mg group and 6.7% in the placebo group. Overall, rate and time to treatment discontinuation were similar among treatment groups.

CONCLUSIONS

Long-acting naltrexone was well tolerated and resulted in reductions in heavy drinking among treatment-seeking alcohol-dependent patients during 6 months of therapy. These data indicate that long-acting naltrexone can be of benefit in the treatment of alcohol dependence.

Determination of Nalmefene by High-Performance Liquid Chromatography-Electrospray Ionization-Tandem Mass Spectrometry

Nalmefene is an opioid antagonist used in the treatment of alcoholism and opioid overdose. A highly sensitive method was developed to measure nalmefene in human and rabbit plasma and rabbit serum. Nalbuphine was used as internal standard. Liquid-liquid extraction was applied using n-butyl chloride/acetonitrile (4:1). High-performance liquid chromatography interfaced by electrospray ionization to a tandem mass spectrometer was used for quantitation. Primary validation experiments were conducted using human plasma then it was cross-validated in rabbit plasma and rabbit serum. Specificity (peak-area ratio of blank plasma or serum to its internal standard as percent of peak-area ratio of blank plasma or serum fortified with 0.1 ng/mL nalmefene to its internal standard) ranged from 2.09 to 5.29 with a mean of 3.21% for human plasma and from 4.08 to 6.63 with a mean of 5.55% for rabbit plasma and from 2.47 to 6.17 with a mean of 3.62% for rabbit serum. The mean recovery for nalmefene was 80% in human plasma. The calibration range was from 0.1 to 100 ng/mL. Intrarun accuracy of the lower limit of quantitation (0.1 ng/mL) in all matrices was within 18.0% of target with intrarun precision within 13.6%. At 0.3, 35, and 75 ng/mL, the intrarun accuracy in all matrices was within 11.9% of target with intrarun precision within 6.6%. The inter-run accuracy in human plasma was within 8.0% of target with inter-run precision within 6.6%. Nalmefene was stable in human and rabbit plasma and rabbit serum for up to 24 h at room temperature and in human plasma after three freeze-thaw cycles. Following intravenous injection of 5 mg/kg nalmefene to rabbits, the mean area under curve for 0 to 24 h was 1116 (ng)(mL)(-1)(h), and the mean plasma clearance was 67.9 (mL)(min)(-1)(kg)(-1).

Narcotic antagonists in drug dependence: pilot study showing enhancement of compliance with SYN-10, amino-acid precursors and enkephalinase inhibition therapy

We decided to test the hypothesis that possibly by combining a narcotic antagonist and amino-acid therapy consisting of an enkephalinase inhibitor (D-phenylalanine) and neurotransmitter precursors (L-amino- acids) to promote neuronal dopamine release might enhance compliance in methadone patients rapidly detoxified with the narcotic antagonist Trexan (Dupont, Delaware). In this regard, Thanos et al. [J. Neurochem. 78 (2001) 1094] and associates found increases in the dopamine D2 receptors (DRD2) via adenoviral vector delivery of the DRD2 gene into the nucleus accumbens, significantly reduced both ethanol preference (43%) and alcohol intake (64%) of ethanol preferring rats, which recovered as the DRD2, returned to baseline levels. This DRD2 overexpression similarly produced significant reductions in ethanol non-preferring rats, in both alcohol preference (16%) and alcohol intake (75%). This work further suggests that high levels of DRD2 may be protective against alcohol abuse [JAMA 263 (1990) 2055; Arch, Gen. Psychiatr. 48 (1991) 648]. The DRD2 A1 allele has also been shown to associate with heroin addicts in a number of studies. In addition, other dopaminergic receptor gene polymorphisms have also associated with opioid dependence. For example, Kotler et al. [Mol. Phychiatr. 3 (1997) 251] showed that the 7 repeat allele of the DRD4 receptor is significantly overpresented in the opioid-dependent cohort and confers a relative risk of 2.46. This has been confirmed by Li et al. [Mol. Psychiatry 2 (1997) 413] for both the 5 and 7 repeat alleles in Han Chinese case control sample of heroin addicts. Similarly Duaux et al. [Mol. Psychiatry 3 (1998) 333] in French Heroin addicts, found a significant association with homozygotes alleles of the DRD3-Bal 1. A study from NIAAA, provided evidence which strongly suggests that DRD2 is a susceptibility gene for substance abusers across multiple populations (2003). Moreover, there are a number of studies utilizing amino-acid and enkephalinase inhibition therapy showing reduction of alcohol, opiate, cocaine and sugar craving behavior in human trials (see Table 1). Over the last decade, a new rapid method to detoxify either methadone or heroin addicts utilizing Trexan sparked interest in many treatment centers throughout the United States, Canada, as well as many countries on a worldwide basis. In using the combination of Trexan and amino-acids, results were dramatic in terms of significantly enhancing compliance to continue taking Trexan. The average number of days of compliance calculated on 1000 patients, without amino-acid therapy, using this rapid detoxification method is only 37 days. In contrast, the 12 subjects tested, receiving both the Trexan and amino-acid therapy was relapse-free or reported taking the combination for an average of 262 days (p < 0.0001F). Thus coupling amino-acid therapy and enkephalinase inhibition while blocking the delta-receptors with a pure narcotic antagonist may be quite promising as a novel method to induce rapid detox in chronic methadone patients. This may also have important ramifications in the treatment of both opiate and alcohol-dependent individuals, especially as a relapse prevention tool. It may also be interesting too further test this hypothesis with the sublingual combination of the partial opiate mu receptor agonist buprenorphrine.

Sensitization to morphine withdrawal in guinea-pigs

The aim of this study was to determine whether sensitization occurred to morphine withdrawal. Guinea-pigs were treated twice daily with increasing doses of morphine (10-100 mg/kg s.c.) for 3 days followed by injection of morphine 100 mg/kg on the fourth day. Sixty min after the last morphine injection, animals were withdrawn from morphine with naltrexone, 15 mg/kg s.c., and locomotor activity and all other behaviours scored over 90 min. Animals were then rested for 3 days. This procedure was repeated twice over the next 2 weeks. Control animals were treated with saline for the first two treatment cycles. Guinea-pigs subjected to three cycles of morphine withdrawal showed a significant increase in the total number of withdrawal behaviour counts over the 90-min observation period following the third cycle of withdrawal compared with the first and second withdrawal cycles. However, locomotor activity, a major sign of morphine withdrawal in guinea-pigs, was not significantly increased. Fos-LI was markedly increased in the repeatedly withdrawn animals in several brain regions, including amygdala, dorsal striatum, thalamus, ventral tegmental area, and ventrolateral periaqueductal gray area. It is concluded that sensitization to morphine withdrawal occurs in guinea-pigs.

Differentiation of opioid receptor preference by [Dmt1]endomorphin-2-mediated antinociception in the mouse

The potent opioid [Dmt1]endomorphin-2 (Dmt-Pro-Phe-Phe-NH2) differentiated between the opioid receptor subtypes responsible for the antinociception elicited by endomorphin-2 in mice. Antinociception, induced by the intracerebroventricular administration of [Dmt1]endomorphin-2 and inhibited by various opioid receptor antagonists [naloxone, naltrindole, beta-funaltrexamine, naloxonazine], was determined by the tail-flick (spinal effect) and hot-plate (supraspinal effect) tests. The opioid receptor subtypes involved in [Dmt1]endomorphin-2-induced antinociception differed between these in vivo model paradigms: naloxone (non-specific opioid receptor antagonist) and beta-funaltrexamine (irreversible mu1/mu2-opioid receptor antagonist) blocked antinociception in both tests, although stronger inhibition occurred in the hot-plate than the tail-flick test suggesting involvement of other opioid receptors. Consequently, we applied naloxonazine (mu1-opioid receptor antagonist) that significantly blocked the effect in the hot-plate test and naltrindole (delta-opioid receptor antagonist), which was only effective in the tail-flick test. The data indicated that [Dmt1]endomorphin-2-induced spinal antinociception was primarily mediated by both mu2- and delta-opioid receptors, while a supraspinal mechanism involved only mu1/mu2-subtypes.

Interactions of "ultra-low" doses of naltrexone and morphine in mature and young male and female rats

Sex and age influence morphine analgesia in humans and animals. Mature rats show greater morphine analgesia in males than in females. Ultra-low doses of naltrexone enhance morphine analgesia. In mature rats (18-22 weeks), naltrexone (0.002-2.0 mg/kg)-morphine (2 mg/kg) cotreatment enhanced morphine analgesia in females, an effect inversely related to naltrexone dose. Conversely, in mature male rats, naltrexone tended to decrease morphine analgesia with increasing dose. In young rats (8-10 weeks), morphine analgesia was unrelated to sex and in both sexes the naltrexone-morphine interaction was negligible. These data show that dose, age, and sex alter the naltrexone-morphine interaction in rats.

Effect of the combination of naltrexone and baclofen, on acquisition of alcohol drinking behavior in alcohol-preferring rats

Recent surveys suggest that positive outcomes in the pharmacotherapy of alcoholism may be obtained through drug combinations. The present study evaluated the effect of the combination of the opioid receptor antagonist, naltrexone, with the GABA(B) receptor agonist, baclofen, on the acquisition of alcohol drinking behavior in Sardinian alcohol-preferring (sP) rats. Rats were treated with either saline, 0.5 mg/kg naltrexone, 1mg/kg baclofen, or 0.5 mg/kg naltrexone plus 1mg/kg baclofen once a day for 10 days. Alcohol was offered immediately after the first drug injection under the 2-bottle regimen. Alcohol intake in saline-treated rats rose to 5-6 g/kg/day within a few days, indicative of a rapid acquisition of alcohol drinking behavior. Neither naltrexone nor baclofen, when given alone, affected alcohol drinking behavior. In contrast, the drug combination resulted in a significant reduction in daily alcohol intake and retardation in the acquisition of alcohol drinking behavior. These results suggest that combination of naltrexone plus baclofen may result in a synergistic reduction in alcohol intake in sP rats. These results are discussed in terms of naltrexone and baclofen exerting a concomitant and reciprocally potentiating inhibitory action on alcohol-induced activation of mesolimbic dopamine transmission.

Measurement of symptom withdrawal severity in a 24-hour period after the anesthesia-assisted rapid opiate detoxification procedure

This study examined the Anesthesia-Assisted Rapid Detoxification (AAROD) procedure and the measurement of withdrawal symptom severity within a 24-hour period. The Clinical Opiate Withdrawal Scale (COWS) was utilized at various time intervals, post detoxification. This study demonstrated that all of the patients who underwent the AAROD procedure had withdrawal symptoms post detoxification in the mild range of severity, unlike like traditional detoxification procedures. Further studies are needed to measure withdrawal symptoms longer than one-day post detoxification and to compare the differences between various detoxification protocols.

Low dose naltrexone therapy in multiple sclerosis

The use of low doses of naltrexone for the treatment of multiple sclerosis (MS) enjoys a worldwide following amongst MS patients. There is overwhelming anecdotal evidence, that in low doses naltrexone not only prevents relapses in MS but also reduces the progression of the disease. It is proposed that naltrexone acts by reducing apoptosis of oligodendrocytes. It does this by reducing inducible nitric oxide synthase activity. This results in a decrease in the formation of peroxynitrites, which in turn prevent the inhibition of the glutamate transporters. Thus, the excitatory neurotoxicity of glutamate on neuronal cells and oligodendrocytes via activation of the alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid class of glutamate receptor is prevented. It is crucial that the medical community respond to patient needs and investigate this drug in a clinical trial.

[The antiarrhythmic effect of (-)-U-50,488 in rats with acute ischemia and reperfusion of heart is mediated by kappa1-opioid receptor activation]

Pretreatment with a selective kappa1 opioid receptor (OR) agonist (-)-U-50,488 (1 mg/kg, i.v.) prevented the development of arrhythmias induced by occlusion (10 min) and reperfusion (10 min) in ketamine anesthetized rats, while the treatment with a less active enantiomer (+)-U-50,488 in the same dose produced no such effects. Preliminary intravenous administration of a selective kappa1 OR antagonist norbinaltorphimine (9 mg/kg) fully abolished the antiarrhythmic effect of (-)-U-50,488, while the kappa2 OR antagonist quadazocine (3 mg/kg) did not eliminate this effect. The injections of norbinaltorphimine or quadazocine alone did not influence the incidence of model arrhythmias caused by the occlusion and reperfusion. It was concluded that kappa1 OR stimulation favors an increase in cardiac tolerance to the arrhythmogenic action of occlusion and reperfusion.

[Safety and effectiveness of opiate antagonist detoxification under general anesthesia]

OBJECTIVE

To evaluate safety and effectiveness of opiate antagonist detoxification under general anesthesia according to available prospective and retrospective data.

METHODS

We analyzed all detoxification cases that were performed in Vilnius University Emergency Hospital in the period of 2002-2005. Data of 65 patients from prospective, randomized, double-blind, placebo-controlled study and 21 retrospective cases were included in the study.

RESULTS

Full opiate receptor blockade was achieved in 85 cases (98.84%). No complications related to detoxification procedure or general anesthesia were recorded. Differences in procedure protocols and possible implications for clinical practice are discussed.

CONCLUSIONS

The protocol of the prospective study may be recommended as a safe and effective detoxification method.

Obstructive cholestasis alters intestinal transit in mice: role of opioid system

Acute cholestasis is associated with increased activity of the endogenous opioid system. It is also known that opioid receptor agonists like morphine decrease the intestinal transit. The purpose of the present study was to investigate the effect of cholestasis on the small intestine transit and the possible involvement of opioid system in this phenomenon in mice. Cholestasis was induced by bile duct-ligation and intestinal transit was measured with charcoal meal and calculation of percent of transit through small intestine. The effect of chronic administration of naltrexone and acute pretreatment with morphine on intestinal transit was evaluated in bile duct-ligated (BDL) as well as unoperated (CTL) and sham-operated (SHAM) animals. The plasma alkaline phosphatase and alanine aminotransferase activities were also measured. A significant decrease in small intestine transit (%transit) was observed in BDL mice compared to SHAM animals, which was prominent even after 24 h of cholestasis. Chronic pretreatment with an opioid receptor antagonist, naltrexone, (10 mg/kg, i.p for 2, 4 or 6 days) completely restored the cholestasis-induced decrease in %transit to that of control animals. Although the acute administration of morphine (2 mg/kg, s.c.) 20 min before charcoal feeding caused a significant decrease in the intestinal transit of CTL and SHAM animals, it did not decrease the %transit of BDL animals on the day 5 after operation. Our findings show that acute cholestasis is associated with a prominent decrease in small intestine transit in mice and opioid receptors maybe involved in this phenomenon.

PHARMACOKINETICS OF CARFENTANIL AND NALTREXONE IN DOMESTIC GOATS (CAPRA HIRCUS)

Using a crossover study design, the pharmacokinetics of carfentanil and naltrexone after i.v., i.m., and s.c. administration were determined in eight domestic goats (Capra hircus). Serial blood samples were taken up to 120 hr after carfentanil administration, and the plasma drug concentrations were determined using liquid chromatography and mass spectroscopy. All goats were immobilized with 40 microg/kg carfentanil i.m., although the resulting neurologic effects varied considerably. Plasma profiles showed rapid carfentanil absorption and a simple biphasic decline for 12-48 hr. Naltrexone given at 100 mg naltrexone/mg carfentanil 30 min after carfentanil administration produced rapid reversal of immobilization after all routes of administration. Variable fluctuations in the naltrexone plasma concentrations during the first 2.5-3.5 hr were observed, followed by a more consistent biphasic decline. The time to standing was significantly shorter after i.v. compared with s.c. naltrexone, although the time difference (1 min) had little clinical relevance. No statistically significant differences between the naltrexone pharmacokinetic parameters measured for the three routes of naltrexone administration were identified, although the recoveries after i.m. administration were, subjectively, the smoothest. The carfentanil half-life did not differ significantly in the goats given naltrexone by different routes. Although it is currently recommended that the naltrexone dose be divided into s.c. and i.v. portions, this practice does not appear to offer any benefit.

Endogenous opioids, µ-opiate receptors and chloroquine-induced pruritus: A double-blind comparison of naltrexone and promethazine in patients with malaria fever who have an established history of generalized chloroquine-induced itching

AIMS

Chloroquine induces a severe generalized pruritus, in predisposed Black African patients, during treatment of malaria fever, and also in some Caucasian patients treated for rheumatological diseases. We have previously shown that chloroquine may release endogenous opioids and/or interact with micro-opiate receptors in rats, and that both histamine and malaria parasite blood density, contribute to the itching severity in malaria fever in humans. The aim of our present study was to assess and compare the antipruritic efficacy of the micro-opiate receptor antagonist, naltrexone, and the antihistamine, promethazine, in chloroquine treated patients with malaria fever.

METHODS

A double-blind, randomized, parallel group comparison of the chloroquine-induced pruritus intensity and time profile in patients with parasitologically proven malaria fever, who were pretreated with a single dose of either naltrexone 50 mg or promethazine 25 mg orally (six patients each). All patients had an established history of severe pruritus following chloroquine treatment of malaria fever. A self-assessed itching severity score was undertaken at 0, 6, 12, 24, 48 and 72 h after initial chloroquine dosing, and the areas under the pruritus-intensity time curve AUCP0-72 h was determined in each patient and correlated to the malaria parasite density in blood.

RESULTS

Both naltrexone and promethazine subjectively reduced itching severity compared with prior historical experience. One patient on naltrexone and two on promethazine never experienced any itching. There was no statistically significant treatment effect, but a significant time effect (P = 0.001, F = 4.77 d.f. 5) by two-way repeated measures ANOVA. The AUCP for naltrexone was 82 +/- 25 units/h, and 57 +/- 34 units/h for promethazine [95% confidence interval for the difference being -73 to 123]. However, the malaria parasite density in the naltrexone group (740 +/- 178 microl(-1)) tended to be higher than in the promethazine group 314 +/- 69 microl(-1) (P = 0.056, 95% confidence interval for the difference being -15 to 866 microl(-1)). Correction of the AUCP for malaria parasite density (parasite pruritogenic index, AUCP. units/h/parasites/microl blood) tended to be lower with naltrexone 9.1 +/- 2.6 than with promethazine 12.2 +/- 7.0 There was a highly significant and positive correlation between the malaria parasite density and the AUCP0-72 h, on naltrexone (r2 = 0.78, P = 0.040) and promethazine (r2 = 0.93, P = 0.008). However, comparison of regressions revealed that the slope of the regression was significantly steeper with promethazine 0.48 than naltrexone 0.12 (P = 0.006, t = 4.2), with the intercepts showing a trend to a difference (P = 0.086).

CONCLUSION

Naltrexone exerted an antipruritic action, at least to a similar extent to promethazine in patients with chloroquine-induced itching in malaria fever. However, the relationship between parasite density and resultant pruritus was significantly different between naltrexone and promethazine. Thus, micro-opiate receptors/and or endogenous opioids may contribute to chloroquine itching in malaria fever, in humans, in accord with animal experimental findings. Malaria parasite density in blood is a strong determinant of itching severity in patients predisposed to chloroquine-induced pruritus.

A comparative study on the effects of naltrexone and loratadine on uremic pruritus

BACKGROUND

Two recent studies have provided opposite results on the efficacy of naltrexone on uremic pruritus. We have performed a third study.

OBJECTIVE

To compare the efficacy and tolerance of naltrexone and loratadine in uremic pruritus.

PATIENTS/METHODS

Among 296 hemodialyzed patients, 65 suffered from uremic pruritus. Fifty-two patients participated in the study. The patients were treated for 2 weeks with naltrexone (50 mg/day; 26 patients) or loratadine (10 mg/day; 26 patients), after a washout of 48 h. Pruritus intensity was scored by a visual analogue scale (VAS). Adverse events were carefully searched for. The two groups were statistically equivalent.

RESULTS

There was no significant difference in the mean VAS scores after treatment, but naltrexone allowed a dramatic decrease in VAS scores (Delta >3/10) in 7 patients. Adverse events (mainly nausea and sleep disturbances) were observed in 10/26 patients.

CONCLUSIONS

Naltrexone is effective only in a subset of patients. Adverse events are very frequent. The differences of efficacy and tolerance between patients might be due to metabolism. Naltrexone might be considered as a second-line treatment.

Implantable technology for long-term delivery of nalmefene for treatment of alcoholism

Pharmacotherapy treatment for alcoholism is limited by poor compliance, adverse effects, and fluctuating drug levels after bolus administration. A long-term delivery system would improve upon these limitations. The current study describes the characterization of a sustained release implant containing nalmefene, an opioid antagonist, for treatment of alcoholism. Nalmefene was blended with ethylene vinyl acetate (EVA), extruded into 2.8 mm x 27 mm rods, and coated with EVA to optimize release. In vitro release was determined by HPLC, and in vivo release characteristics after subcutaneous implantation into rats were determined by LC-MS/MS analyses. Extrusion produced rods containing 80.09 +/- 6.0 mg nalmefene. In vitro release was high from the uncoated rods, and they were depleted of drug fairly quickly; however EVA coatings maintained release over longer periods. The 25 wt.% coated rods provided in vitro release of 0.36 mg/day/rod, and in vivo release of 0.29 mg/day/rod over 6 months, and showed dose-dependent nalmefene plasma concentrations (one rod: 3.33 +/- 0.56 ng/ml, three rods: 10.19 +/- 2.31 ng/ml). After explantation, nalmefene plasma concentrations were undetectable by 6 h. A sustained release nalmefene rod provides 6 months of drug with no adverse effects.

A Pilot Evaluation of the Safety and Tolerability of Repeat Dose Administration of Long-Acting Injectable Naltrexone (Vivitrex??) in Patients With Alcohol Dependence

BACKGROUND

: Oral naltrexone is currently used as part of a treatment regimen for alcohol-dependent patients, but its clinical utility is hampered by poor patient adherence. A long-acting injectable naltrexone formulation (Vivitrex) was designed to facilitate patient adherence by providing an extended duration of therapeutic naltrexone over 1 month, thereby eliminating the need for daily dosing.

METHODS

: A multicenter, randomized, double-blind, placebo-controlled pilot study was conducted to evaluate the safety and tolerability of intramuscular repeat dose administration of this extended-release naltrexone formulation in DSM-IV alcohol-dependent patients. Thirty patients were randomized to treatment with injectable naltrexone (400 mg; n = 25) or a matching placebo injection (n = 5) and were dosed once every 28 days over 4 months. Psychosocial treatment was offered to patients in both treatment groups. Outcome measures related to drinking activity and trough plasma concentrations of naltrexone and its primary metabolite, 6-beta-naltrexol, were evaluated.

RESULTS

: Injectable naltrexone was generally safe and well tolerated. Reported adverse events were mild to moderate and resolved without intervention; only two patients discontinued due to adverse events. The most common adverse events (nausea and headache) occurred at a similar rate for patients in both treatment groups. Pharmacokinetic analysis confirmed that therapeutic levels of naltrexone were delivered throughout the four 1-month treatment cycles.

CONCLUSIONS

: The results of this pilot study provide the basis and methods for a larger, more definitive trial to determine the utility of this long-acting injectable naltrexone formulation in the treatment of alcohol-dependent patients.

What place does naltrexone have in the treatment of alcoholism?

Despite two recent negative trials, most controlled clinical studies have found that when naltrexone is added to substance abuse treatment or counselling, significantly less heavy drinking is done by the patients who are willing to take most of the prescribed naltrexone. Naltrexone also reduces urges to drink and makes any slips back into drinking less pleasant. Therefore, naltrexone can be a useful adjunct to substance abuse counselling or rehabilitation programmes, as one of many tools that clinicians and patients use. However, beneficial effects are limited in scope. Naltrexone mostly does not increase the chance of staying completely abstinent but rather reduces the intensity or frequency of any drinking that does occur. Many alcohol-dependent individuals are medically ineligible or are unwilling to take naltrexone, many who start naltrexone do not continue with it and many who comply with it do not benefit. Compliance is greater for individuals who experience fewer adverse effects and who have stronger beliefs in the benefits of naltrexone, suggesting that clinicians can increase compliance by helping patients to manage adverse effects and by bolstering patients' beliefs in the benefits of naltrexone. Alcohol-dependent individuals who are most likely to benefit from naltrexone seem to be those with close relatives who also had alcohol problems, or who have stronger urges to drink or who are more limited in cognitive abilities. Some individuals may benefit from a higher dose, particularly people with lower blood concentrations of the medication, and individuals who achieve good results may benefit from a longer course of treatment with naltrexone. In these ways, treatment can be targeted to increase the likelihood of beneficial outcomes with naltrexone.

Instrumental learning within the spinal cord: III. Prior exposure to noncontingent shock induces a behavioral deficit that is blocked by an opioid antagonist

Spinally transected rats given legshock whenever one hindleg is extended learn to maintain a flexion response that decreases net shock exposure. Prior exposure to response-independent (noncontingent) shock prevents learning. This behavioral deficit was eliminated by systemic administration of the nonselective opioid antagonist naltrexone (Experiment 1). The deficit was also blocked by intrathecal (i.t.) naltrexone at a dose of 7 microg/microl (Experiment 2). Noncontingent shock undermined behavioral potential for 24 h (Experiment 3). The expression of the deficit was blocked by naltrexone (7 microg/microl, i.t.) given prior to testing. The same dose prior to initial shock exposure had no effect. Administration of an antagonist that acts on the kappa opioid receptor (nor-BNI) restored learning (Experiment 4). Equal molar concentrations of antagonists that act on the micro (CTOP) or delta (naltrindole) receptor had no effect.