Induction of opioid-dependent individuals onto buprenorphine and buprenorphine/naloxone soluble-films.

A sublingual soluble-film formulation of buprenorphine/naloxone (B/N) has been approved by the US Food and Drug Administration for the treatment of opioid dependency. This preparation provides unit-dose, child-resistant packaging amenable to tracking and accountability, offers more rapid dissolution, and has a potentially preferred taste vs. tablets. This study compared the ability of buprenorphine (B) and B/N films to suppress spontaneous withdrawal in opioid-dependent volunteers. Participants were maintained on morphine and underwent challenge sessions to confirm sensitivity to naloxone-induced opioid withdrawal. Subjects were randomized to receive either B (16 mg, n = 18) or B/N (16/4 mg, n = 16) soluble films for 5 days. The primary outcome measure was the Clinical Opiate Withdrawal Scale (COWS) score. Thirty-four subjects completed induction onto soluble films. There was a significant decrease in COWS scores but no significant differences between the groups. The results support the use of B and B/N soluble films as safe and effective delivery methods for opioid induction.

Evaluation of the mu and kappa opioid actions of butorphanol in humans through differential naltrexone blockade.

RATIONALE: Butorphanol exerts activity at mu, kappa, and delta opiate receptors in rats and monkeys but produces predominant mu-like effects in humans. OBJECTIVES: The aim of this study was to determine if the kappa receptor-mediated actions of butorphanol could be unmasked or enhanced by giving it in combination with naltrexone, an opioid antagonist with higher affinity for mu vs kappa receptors. MATERIALS AND METHODS: Ten healthy adult inpatient volunteers (eight men, two women), with opioid abuse histories, completed this double-blind, randomized, placebo-controlled study. Naltrexone (0, 1, 3, 10, or 30 mg, p.o.) was administered 1 h before butorphanol (0, 6, or 12 mg/70 kg, i.m.) during 15 test sessions. An array of physiological (e.g., vital signs, urine output, and subject- and observer-rated) measures was collected before and for 4 h after drug administration. RESULTS: Naltrexone alone produced no direct effects. Butorphanol alone produced typical mu-, but not kappa-, related physiological effects (e.g., miosis, respiratory depression) and produced mood and drug effects considered typical of both mu (e.g., "liking," "good drug effects") and kappa agonists (e.g., increases in perceptual disturbances). Naltrexone pretreatment led to significant butorphanol-induced diuresis (i.e., increased urine output and decreased urine osmolality). Naltrexone generally produced a dose-dependent blockade of subjective responses. CONCLUSION: These data suggest that naltrexone antagonism unveiled the kappaergic activity of butorphanol as measured by diuresis, while subjective responses generally attributed to mu vs kappa receptors were not dissociable. Moreover, these data demonstrate that butorphanol exerts physiologically relevant kappa agonist activity at these supraanalgesic doses in humans.

A validated liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry method for quantitation of cocaine and benzoylecgonine in human plasma.

In order to support studies on various medication protocols for the treatment of cocaine abuse, an accurate, precise, and sensitive (2.5 to 750 ng/mL) liquid chromatography-tandem mass spectrometry assay was developed to determine cocaine and benzoylecgonine in human plasma. Cocaine-d3 and benzoylecgonine-d3 were added as internal standards and samples were subjected to solid-phase extraction. Cocaine recovery was 94.4% and benzoylecgonine was 80.3% at 2.5 ng/mL. The selected reaction monitoring of parent ions at m/z 304 and 290 resulted in strong fragments at m/z 182 and 168 for cocaine and benzoylecgonine, respectively. The method was fully validated. The mean measured concentration at the 2.5 ng/mL, the lower limit of quantitation, was within 10.8% of the target and the precision determined at the low (5 ng/mL), medium (50 ng/mL), and high (650 ng/mL) quality controls ranged from 0.9 to 6.2 %CV. Cocaine and benzoylecgonine concentrations in plasma treated with 1% NaF showed changes of less than 10% when maintained at room temperature for up to 7 h and no significant changes when subjected to three freeze-thaw cycles. The concentrations of cocaine and benzoylecgonine remained stable in plasma samples stored at -20 degrees C for up to 11 months. Methanolic stock solutions of both analytes are stable, staying within 2% of the freshly prepared stock solutions, when stored at -20 degrees C for up to 235 days. Both extracted analytes reconstituted in methanolic solutions are stable for up to seven days whether stored at -20 degrees C or at room temperature on the autosampler. The method is rugged, rapid, and robust and has been applied to the batch analysis of more than 700 samples during pharmacokinetic profiling to assess potential interactions between intravenous (i.v.) cocaine challenge and treament medications. Results from three of these subjects receiving 40 mg (i.v.) cocaine demonstrate the utility of the method.

Enadoline, a selective kappa opioid agonist: comparison with butorphanol and hydromorphone in humans.

RATIONALE: The availability of the highly selective and specific kappa opioid agonist enadoline provides an opportunity to explore the function of kappa receptors in humans and their potential utility as a target for substance abuse pharmacotherapy development. OBJECTIVES: The purpose of this study was to characterize the pharmacodynamic effects of enadoline, a selective kappa agonist, and to compare it with butorphanol, a mixed mu/kappa agonist, and hydromorphone, a mu agonist, in humans. METHODS: Pilot evaluation (n=3) served to establish intramuscular doses of enadoline (20, 40, 80, and 160 microg/70 kg), butorphanol (1.5, 3, 6, and 12 mg/70 kg), and hydromorphone (1.5, 3, and 6 mg/70 kg) of comparable activity. These acute doses were examined under double-blind, placebo-controlled and constrained randomized conditions with a minimum of 72 h between tests in volunteers with polysubstance abuse histories (n=6). Physiological and subject- and observer-rated measures were collected 30 min before and for 4 h after administration. RESULTS: Enadoline significantly increased measures of sedation, confusion and dizziness, produced visual distortions and feelings of depersonalization, and increased urinary output. The highest dose (160 microg/70 kg) was not tolerated and led to psychotomimetic effects. Hydromorphone produced prototypic mu opioid effects including respiratory depression, miosis, and euphoria. Butorphanol was most similar to hydromorphone and shared few effects with enadoline. CONCLUSIONS: These results are discussed with respect to the potential use and safety of kappa agonists for clinical indications.

Effect of flupenthixol on subjective and cardiovascular responses to intravenous cocaine in humans.

The effects of oral flupenthixol and intramuscular (i.m.) flupenthixol decanoate in combination with intravenous (i.v.) cocaine were evaluated in male cocaine abusers. Participants resided at an inpatient research unit for 27 days followed by an 11-day outpatient period. Oral flupenthixol (2.5 or 5.0 mg; p.o.) followed by flupenthixol decanoate (10 or 20 mg; i.m.) and placebo were investigated in individuals who were randomly assigned to one of three groups under double-blind conditions (placebo, low or high dose flupenthixol). During the inpatient period, participants had four fixed cocaine dosing sessions; each session they were administered four doses of i.v. cocaine (approx. 48 mg/70 kg), spaced 14 min apart. These sessions occurred once before medication (baseline phase), once following oral medication (oral phase), and twice following intramuscular medication (IM phase). Out of 23 participants, 18 completed the study; 4 of the 5 non-completers were in the high dose flupenthixol group. Overall, there were few subjective, cardiovascular, or cocaine pharmacokinetic differences between the placebo group and the low dose flupenthixol group, indicating that the low dose of flupenthixol was well tolerated, but ineffective. In the high dose flupenthixol group, two out of seven individuals (29%) experienced a dystonic reaction following oral flupenthixol and were medically discharged. Taken together, these findings indicate that flupenthixol is not a good candidate for treating cocaine abusers.

Voucher-based reinforcement of opiate plus cocaine abstinence in treatment-resistant methadone patients: effects of reinforcer magnitude.

The study tested a voucher-based abstinence reinforcement procedure for reducing opiate and cocaine use in a population of treatment-resistant opiate- and cocaine-abusing methadone patients. Vouchers exchangeable for goods and services were contingent on abstinence from both opiates and cocaine. In two conditions, participants could earn up to $374 or $3,369 in vouchers for providing opiate- and cocaine-free urine samples. Participants received a daily 60-mg dose of methadone. The dose was increased in a second phase, and the voucher conditions were replicated. Analyses of both phases revealed trends toward greater abstinence under the high voucher condition and suggested that higher doses may enhance the efficacy of voucher reinforcement. The results show that reinforcement for abstinence from 2 drugs simultaneously can be effective even in a treatment-resistant population.

Enadoline and butorphanol: evaluation of kappa-agonists on cocaine pharmacodynamics and cocaine self-administration in humans.

Preclinical studies have demonstrated that kappa-opioid agonists can attenuate the neurochemical and behavioral effects of cocaine that are related to its reinforcing efficacy, suggesting that kappa-agonists may serve as pharmacotherapies for cocaine dependence. This 8-week inpatient study examined the ability of enadoline, a selective and high-efficacy kappa-agonist, and butorphanol, a mixed agonist with intermediate efficacy at both mu- and kappa-receptors, to reduce the direct pharmacodynamic effects and self-administration of intravenous cocaine in humans (n = 8). Acute doses of intramuscular enadoline (20, 40, and 80 microg/kg), butorphanol (1.5, 3, and 6 mg/70 kg) and placebo were examined separately as pretreatments during each of three test sessions with cocaine in a constrained random order. A cocaine dose-effect session (0, 20, and 40 mg cocaine i.v., 1 h apart) examined direct pharmacodynamic interactions on subjective and physiological indices; self-administration sessions examined choice behavior for cocaine (40 mg i.v. for six trials) versus money 1) in the presence of a sample cocaine dose with money choices presented in ascending value, and 2) in the absence of a sample dose with money choices presented in descending values. Enadoline (80 microg/70 kg) significantly (p < 0.05) reduced some of the positive subjective effects of cocaine (e.g., ratings of "high"), while butorphanol failed to modify subjective responses. Both agents were safely tolerated in combination with cocaine without adverse physiological responses. Cocaine self-administration was significantly greater across all pretreatment conditions when the sample dose was given and ascending money choices were used. Enadoline and butorphanol failed to modify cocaine self-administration. These data suggest that these kappa-agonists may be safely administered in the presence of cocaine but do not produce significant attenuation of cocaine's direct effects or self-administration under these acute dosing conditions.

A reinforcement-based therapeutic workplace for the treatment of drug abuse: six-month abstinence outcomes.

This study evaluated a novel drug abuse treatment, the Therapeutic Workplace. In this treatment, patients are paid to perform jobs or to participate in job training. Salary is linked to abstinence by requiring patients to provide drug-free urine samples to gain access to the workplace. Pregnant and postpartum drug abuse patients (N = 40) were randomly assigned to a Therapeutic Workplace or usual care control group. Therapeutic Workplace participants were invited to work 3 hr every weekday for 6 months and could earn up to $4,030 in vouchers for abstinence, workplace attendance, and performance. On average, 45% of participants attended the workplace per day. Relative to controls, the Therapeutic Workplace nearly doubled patients' abstinence from opiates and cocaine (33% vs. 59% of thrice-weekly urine samples drug negative, respectively, p < .05). The Therapeutic Workplace can effectively treat heroin and cocaine abuse in pregnant and postpartum women.

Gradual dose taper following chronic buprenorphine.

This paper describes the time course of withdrawal and relapse in opioid-dependent volunteers (n = 8) who completed a gradual outpatient buprenorphine dose taper (28 days). Compliance with treatment was very high, as evidenced by clinic attendance (96-100%). Urinalysis showed that 6 of the 8 volunteers had relapsed to opiates by the end of the dose taper, even though reports of withdrawal were generally low. Relapse may have been triggered by a desire to re-experience the drug's positive subjective effects, craving, or low motivation to remain drug-free. A longer taper combined with an expanded range of treatments may improve prognosis.

Repeated administration of the D1/5 antagonist ecopipam fails to attenuate the subjective effects of cocaine.

RATIONALE: Dopaminergic compounds have been targeted as potential treatments for cocaine abuse because of the known role of dopamine systems in drug reinforcement. Recent preclinical and human data have focused on the D1/5 antagonist, SCH 39166 (ecopipam), as a potential therapeutic agent. OBJECTIVES: The objective of the present study was to determine whether treatment with chronic ecopipam can blunt or block the subjective effects of cocaine in the absence of significant behavioral impairment or toxic physiological effects. METHODS: Four doses of ecopipam (0, 10, 25, and 100 mg p.o.) were administered daily for 1 week each in double-blind, random order to inpatient cocaine-dependent volunteers (n = 10). Cocaine challenge doses (0, 25, and 50 mg/70 kg i.v.) were administered on the 7th day in ascending order, 1 h apart. RESULTS: Ecopipam alone produced reliable dose-dependent deficits in performance on the digit symbol substitution task (DSST) and the circular lights task, but not a balance task. Impairment on the DSST waned with repeated dosing suggesting the development of tolerance. Ecopipam resulted in few direct subjective effects. Cocaine alone produced dose-dependent changes in prototypic subjective and physiological measures, however, ecopipam largely failed to alter either cocaine's direct effects or the desire for cocaine. CONCLUSIONS: Although the performance effects verify that these doses of ecopipam were behaviorally active, the absence of an attenuation of cocaine's effects of craving for cocaine in this chronic dosing paradigm suggests this compound is unlikely to be an effective pharmacotherapy for cocaine abuse.

Effects of buprenorphine/naloxone in opioid-dependent humans.

RATIONALE: Buprenorphine is a partial mu opioid agonist under development as a sublingual (SL) medication for opioid dependence treatment in the United States. Because buprenorphine may be abused, tablets combining buprenorphine with naloxone in a 4:1 ratio have been developed to reduce that risk. Low doses of injected buprenorphine/naloxone have been tested in opioid-dependent subjects, but higher doses (more than 2 mg of either medication) and direct comparisons to SL buprenorphine/naloxone have not been examined. OBJECTIVES: To assess and compare the effects of intramuscular (i.m.) versus SL buprenorphine/naloxone in opioid-dependent volunteers. METHODS: Opioid-dependent volunteers were maintained on 40 mg per day of oral hydromorphone while on a residential research ward. After safety testing in two pilot subjects, participants (n = 8) were tested with both i.m. and SL buprenorphine/naloxone (1/0.25, 2/0.5, 4/1, 8/2, 16/4 mg); i.m. hydromorphone (10 mg) and naloxone (0.25 mg); both i.m. and SL buprenorphine alone (8 mg); and placebo. Test sessions were twice per week; dosing was double-blind. RESULTS: Intramuscular buprenorphine/naloxone produced dose-related increases on indices of opioid antagonist effects. Effects were consistent with naloxone-precipitated withdrawal, and were short-lived. As withdrawal effects dissipated, euphoric opioid agonist effects from buprenorphine did not appear. Sublingual buprenorphine/naloxone produced neither opioid agonist nor antagonist effects. CONCLUSIONS: Intramuscular injection of buprenorphine/naloxone precipitates withdrawal in opioid dependent persons; therefore, the combination has a low abuse potential by the injection route in this population. Sublingual buprenorphine/naloxone by tablet is well tolerated in opioid dependent subjects, and shows neither adverse effects (i.e., precipitated withdrawal) nor a high abuse potential (i.e., opioid agonist effects).

Effect of intravenous injection speed on responses to cocaine and hydromorphone in humans.

RATIONALE: It is commonly accepted that the relative abuse liability of drugs is positively related to the rate of delivery to the central nervous system; however, few controlled studies have tested this hypothesis in humans. OBJECTIVES: The aims of this study were to evaluate systematically the effects of modifying intravenous infusion speed on the pharmacodynamic responses related to abuse liability and toxicity of intravenous cocaine and hydromorphone. METHODS: Twelve experienced opiate and cocaine users completed this 3-week inpatient study. After completing a safety session, participants were tested on 9 separate test days with intravenous cocaine (30 mg/70 kg), hydromorphone (3 mg/70 kg), and placebo, each administered under double-blind and randomized conditions at infusion rates of 2, 15, and 60 s. Dependent outcome measures included a range of physiological, subjective, and observer-rated measures, and continuous electrocardiographic monitoring was conducted for safety monitoring. RESULTS: Subjective responses to cocaine (for example, "high," "liking") were significantly greater when cocaine was infused more rapidly. Physiological responses to cocaine were largely unaltered with no evidence of increased toxicity with faster infusion speeds. None of the effects of hydromorphone were altered by varying the speed of infusion. CONCLUSIONS: This study provides empirical evidence for the commonly accepted belief that the abuse liability of cocaine can be enhanced by increasing the rate of the intravenous infusion; this principal may not hold true for opioids but further work would be required to rule this out. The data also indicate that moderate doses of cocaine can be administered over a range of infusion speeds commonly used in experimental settings without appreciably altering the apparent medical risks.

A comparison of levomethadyl acetate, buprenorphine, and methadone for opioid dependence.

BACKGROUND: Opioid dependence is a chronic, relapsing disorder with important public health implications. METHODS: In a 17-week randomized study of 220 patients, we compared levomethadyl acetate (75 to 115 mg), buprenorphine (16 to 32 mg), and high-dose (60 to 100 mg) and low-dose (20 mg) methadone as treatments for opioid dependence. Levomethadyl acetate and buprenorphine were administered three times a week. Methadone was administered daily. Doses were individualized except in the group assigned to low-dose methadone. Patients with poor responses to treatment were switched to methadone. RESULTS: There were 55 patients in each group; 51 percent completed the trial. The mean (+/-SE) number of days that a patient remained in the study was significantly higher for those receiving levomethadyl acetate (89+/-6), buprenorphine (96+/-4), and high-dose methadone (105+/-4) than for those receiving low-dose methadone (70+/-4, P<0.001). Continued participation was also significantly more frequent among patients receiving high-dose methadone than among those receiving levomethadyl acetate (P=0.02). The percentage of patients with 12 or more consecutive opioid-negative urine specimens was 36 percent in the levomethadyl acetate group, 26 percent in the buprenorphine group, 28 percent in the high-dose methadone group, and 8 percent in the low-dose methadone group (P=0.005). At the time of their last report, patients reported on a scale of 0 to 100 that their drug problem had a mean severity of 35 with levomethadyl acetate, 34 with buprenorphine, 38 with high-dose methadone, and 53 with low-dose methadone (P=0.002). CONCLUSIONS: As compared with low-dose methadone, levomethadyl acetate, buprenorphine, and high-dose methadone substantially reduce the use of illicit opioids.

Effects of agonist-antagonist opioids in humans trained in a hydromorphone/not hydromorphone discrimination.

The purpose of this study was to examine the discrimination of agonist-antagonist opioids in humans trained in a two-choice hydromorphone/not hydromorphone discrimination. Eight adult male volunteers with histories of opioid abuse who were not currently physically dependent were trained to discriminate the mu receptor agonist hydromorphone (3 mg/70 kg, i.m.) ("Drug A") from a "Not Drug A" training condition (saline placebo). Volunteers received financial reinforcement for correct responses. After training, generalization dose-effect curves for hydromorphone, butorphanol, pentazocine, nalbuphine, and buprenorphine were determined. Other subjective, behavioral, and physiological measures were concurrently collected in all sessions. In generalization testing hydromorphone and buprenorphine produced dose-related increases in hydromorphone-appropriate responses. Pentazocine produced an inverted U-shaped dose-response curve with complete substitution at 32 mg/70 kg but not at 64 mg/70 kg. Butorphanol and nalbuphine did not completely substitute for hydromorphone at any dose tested. These results differ from an earlier two-choice, Drug A versus Drug B (hydromorphone/saline) discrimination study. After Drug/Not Drug instructions the behavioral discriminations of agonist-antagonist opioids were more consistent with their putative agonist activities at the mu opioid receptor and with their subjective effects profiles than was the case after Drug A versus Drug B instructions. These results suggest that instructions are an important factor in the outcome of human drug discrimination studies.

Modulation of intravenous cocaine effects by chronic oral cocaine in humans.

RATIONALE: Agonist therapies have proven effective for the treatment of substance dependence disorders; limited data is available on their feasibility for treating cocaine dependence. OBJECTIVES: This laboratory study was designed to test the safety and utility of employing an agonist substitution therapy for the treatment of cocaine dependence in humans. METHODS: Oral cocaine served as the agonist treatment and was administered chronically over a range of doses to volunteers with cocaine abuse histories (n=8). Oral capsules were administered daily under blind conditions (q.i.d.) during this 5-week inpatient study using a dose-rising sequence (0 mg 10 days: 25 mg 3 days, 50 mg 4 days, 100 mg 10 days, 0 mg 7 days). During each of these oral dosing periods, an i.v. cocaine challenge (0, 25, and 50 mg, 1 h apart) was administered at least once. Physiological, subjective and pharmacokinetic measures were collected before and after i.v. drug administration; additional measures were collected daily. RESULTS: Oral cocaine produced no subjective effects or signs of toxicity but produced dose-related physiological effects. Significant interactions between oral and i.v. cocaine were observed; cocaine (100 mg, p.o.) significantly decreased responses to the 25-mg but not the 50-mg dose of i.v. cocaine for heart rate, mydriasis, and some subjective measures. There was no evidence of significant additive effects, although heart rate responses to i.v. cocaine were exaggerated during the final wash-out period. CONCLUSIONS: These data indicate that treatment with a cocaine "agonist" - in this case oral cocaine - can modestly attenuate the subjective and physiological responses to cocaine in humans under conditions that are safely tolerated.

Effects of buprenorphine versus buprenorphine/naloxone tablets in non-dependent opioid abusers.

RATIONALE: Buprenorphine is an opioid agonist-antagonist under development in the United States as a sublingual medication for treatment of opioid dependence. Buprenorphine may be abused; therefore, tablets combining buprenorphine with naloxone have been developed with the intent of reducing the abuse risk in people physically dependent upon opioids. The characteristics and abuse potential of buprenorphine and buprenorphine/naloxone tablets in non-dependent opioid abusers have not been determined. Non-parenteral abuse of opioids such as buprenorphine may be more likely in people who have less severe substance abuse disorders (e.g., are not physically dependent upon opioids). OBJECTIVES: To assess the abuse potential of sublingual buprenorphine and buprenorphine/naloxone tablets in non-dependent opioid abusers. METHODS: Subjects (n=7) were tested with sublingual buprenorphine (4, 8, 16 mg), sublingual buprenorphine/naloxone (1/0.25, 2/0.5, 4/1, 8/2, 16/4 mg), as well as intramuscular hydromorphone as an opioid agonist control (2, 4 mg) and placebo in laboratory sessions conducted twice per week. Dosing was double-blind and double-dummy. RESULTS: The higher doses of both buprenorphine and buprenorphine/naloxone produced similar opioid agonist-like effects. The onset of these effects was slowed, consistent with the sublingual route of administration, and the magnitude of effects was moderate. There was no evidence to suggest the addition of naloxone attenuated buprenorphine's opioid agonist effects in this population when buprenorphine was delivered by the sublingual route. CONCLUSIONS: These results suggest that sublingual buprenorphine and buprenorphine/naloxone may both be abused by opioid users who are not physically dependent upon opioids.

The brief abstinence test: voucher-based reinforcement of cocaine abstinence.

This study assessed the effectiveness of a brief abstinence reinforcement procedure for initiating cocaine abstinence in methadone maintenance patients. On Monday of the test week, 72 cocaine-abusing methadone patients were offered a $100 voucher if urine samples collected on Wednesday indicated that they had abstained from cocaine across that 2-day period. A patient was considered abstinent and the voucher delivered if the urine benzoylecgonine concentration decreased by 50% from Monday to Wednesday (quantitative criterion) or if the concentration of Wednesday's urine sample was < or = 300 ng/ml. Overall, 79% of study patients showed urinalysis evidence of abstention from cocaine between Monday and Wednesday of the test week. In a subsample with complete data (n = 50), significantly more patients abstained from cocaine from Monday to Wednesday of the test week (84%) than from Monday to Wednesday of the week before (36%) or after (32%) the test week. Furthermore, while almost all patients (94%) decreased their benzoylecgonine concentration from Monday to Wednesday of the test week, significantly fewer patients' benzoylecgonine concentrations decreased from Monday to Wednesday of the week before (56%) or after (48%) the test week. This highly efficacious procedure may have clinical application where reliable abstinence initiation is desired, either on a temporary basis (e.g. sobriety sampling) or at the start of longer-term interventions. It may also be possible to use the brief abstinence test as an experimental model to assess the effects of other therapeutic interventions on abstinence initiation in treatment settings.

Voucher-based reinforcement of cocaine abstinence in treatment-resistant methadone patients: effects of reinforcement magnitude.

Voucher-based reinforcement of cocaine abstinence has been one of the most effective means of treating cocaine abuse in methadone patients, but it has not been effective in all patients. This study was designed to determine if we could promote cocaine abstinence in a population of treatment-resistant cocaine abusing methadone patients by increasing the magnitude of voucher-based abstinence reinforcement. Participants were 29 methadone patients who previously failed to achieve sustained cocaine abstinence when exposed to an intervention in which they could earn up to $1155 in vouchers (exchangeable for goods/services) for providing cocaine-free urines. Each patient was exposed in counterbalanced order to three 9-week voucher conditions that varied in magnitude of voucher reinforcement. Patients were exposed to a zero, low and high magnitude condition in which they could earn up to $0, $382, or $3480 in vouchers for providing cocaine-free urines. Analyses for 22 patients exposed to all three conditions showed that increasing voucher magnitude significantly increased patients' longest duration of sustained cocaine abstinence (P<0.001) and percent of cocaine-free urines (P<0.001), and significantly decreased patients' reports of cocaine injections (P=0.024). Almost half (45%) of the patients in the high magnitude condition achieved >/=4 weeks of sustained cocaine abstinence, whereas only one patient in the low and none in the zero magnitude condition achieved more than 2 weeks. Reinforcement magnitude was a critical determinant of the effectiveness of this abstinence reinforcement intervention.

Assessment of opioid partial agonist activity with a three-choice hydromorphone dose-discrimination procedure.

The discriminative stimulus and subjective effects of opioid mixed agonist-antagonists were assessed in volunteer nondependent heroin users trained in a three-choice drug discrimination procedure to discriminate among the effects of i.m. administration of 2 ml of saline, 1 mg of hydromorphone, and 4 mg of hydromorphone (a morphine-like mu agonist). Other subjective, behavioral, and physiological measures were concurrently collected. The discrimination was readily learned by six of the eight subjects. After training, generalization curves were determined for the following i.m. drug conditions: hydromorphone (0.375-4.0 mg), pentazocine (7.5-60 mg), butorphanol (0.75-6 mg), nalbuphine (3-24 mg), and buprenorphine (0.075-0.6 mg). All five of the test drugs were discriminated significantly or showed trends toward being discriminated as hydromorphone 1 mg-like at one or more dose levels. Hydromorphone showed an inverted U-shaped dose-effect function on the hydromorphone 1 mg-like discrimination. Subjective effect measures produced clearer differentiation among the test drugs than did drug discrimination performance. The present results differ from those of a previous study that observed a close relationship between the results of the discrimination measure and subjective effect measures. The previous study used similar methods and test drugs but different training drugs (e.g., 3 mg of hydromorphone versus 6 mg of butorphanol versus saline). It appears that both the sensitivity of drug discrimination performance to between-drug differences and the relationship between discriminative and subjective effects depends upon the specific discrimination that is trained (e.g., two-choice or three-choice). The present high dose-low dose-saline discrimination procedure appears useful for assessing partial agonist activity. The present data are consistent with partial agonist activity for pentazocine, butorphanol, nalbuphine, and buprenorphine.

Relative potency of levo-alpha-acetylmethadol and methadone in humans under acute dosing conditions.

levo-alpha-Acetylmethadol (LAAM) and methadone are full mu-opioid agonists used to treat opioid dependence. Current labeling indicates that LAAM is less potent than methadone. Clinical studies have not determined the relative potency of these drugs. This study compared the effects of acute doses of LAAM and methadone and also examined the ability of naloxone to reverse their effects. Five occasional opioid users received once weekly doses of either placebo, LAAM, or methadone (15, 30, or 60 mg/70 kg p.o.) in agonist exposure sessions and then received naloxone (1.0 mg/70 kg i.m.) 24, 72, and 144 h after agonist exposure. Subject-rated, observer-rated, and physiological measures were assessed regularly. Comparisons of physiological and subjective measures collected in agonist exposure sessions indicate that LAAM is not less potent than methadone under acute dosing conditions. For some measures, LAAM was significantly more potent. Three subjects who entered the study were withdrawn for safety reasons due to greater than anticipated and clinically relevant respiratory depression after receiving 60 mg of LAAM. Naloxone did not fully reverse the pupil constriction produced by 60 mg of LAAM. Acute agonist effects suggest that LAAM may be more potent than methadone and more potent than current labeling indicates. An accurate LAAM:methadone relative potency estimate will aid determination of adequate doses for opioid-dependent patients inducted onto LAAM and for methadone maintenance patients who choose to switch to more convenient thrice-weekly LAAM.