Diazepam and methadone blood levels following concurrent administration of diazepam and methadone

Results of a previous study indicated that the opioid effects of methadone were enhanced by the concurrent administration of diazepam in methadone-maintained subjects. To determine whether a pharmacokinetic interaction might account for this methadone-diazepam interaction, the plasma levels of methadone, diazepam and diazepam metabolites were determined in blood samples collected during that study. Five adult male patients on methadone maintenance (50-60 mg/day) were administrated single doses of placebo, diazepam (20 and 40 mg), methadone (100%, 150% and 200% of the maintenance dose), and four diazepam-methadone dose combinations (20 and 40 mg diazepam in combination with 100% and 150% of the maintenance dose). The results showed that the concurrent administration of methadone and diazepam did not significantly change the time-course or areas under the plasma concentration-time curve of methadone, diazepam or N-desmethyl-diazepam compared to the levels following the administration of either drug alone. Thus, plasma drug level analysis does not indicate a pharmacokinetic interaction between diazepam and methadone.

Comparison of intravenously administered methadone, morphine and heroin

Data from previously reported studies suggest that methadone may be more euphorigenic than other morphine-like drugs. To determine whether methadone is more potent in producing euphoria relative to its other opiate-like effects, single doses of intravenously administered methadone, morphine, heroin and placebo were compared in non-dependent post-addict volunteers. Morphine-like physiologic, subjective and behavioral effects were measured periodically for 24 h after drug administration. Under the conditions of the experiment methadone produced a profile of effects which was indistinguishable from that of morphine and heroin. Only the time course of miosis, which was longer lasting following methadone, differentiated among the three compounds. The relative potencies of methadone, morphine and heroin for the initial 5 h of effect were constant over all opiate-like effects, including measures of euphoria. Thus, methadone was not a selective euphoriant.

Evaluation of mixtures of morphine and d-amphetamine for subjective and physiological effects

Combinations of morphine and d-amphetamine have been shown to be more effective in relieving pathological and experimental pain with fewer side effects than morphine alone. Subjective, physiological and behavioral effects of the combination were assessed in the present study to determine whether the abuse liability of the combination might also be enhanced. Single intramuscular doses of morphine and d-amphetamine alone and in combination were tested under double-blind conditions in 10 adult, male, non-dependent substance abusers. Morphine and amphetamine alone increased scores on subjective effect measures including the Morphine-Benzedrine Group (MBG) (euphoria) and liking scales. In general, the combination produced greater euphoria than that produced by either drug alone. In contrast, many physiological effects of the drugs were mutually antagonized. Thus, the combination of morphine and d-amphetamine has a greater potential to be abused because of the additive euphoria and a lessening of side effects.

Methamphetamine, physostigmine, atropine and mecamylamine: effects on force lever performance

Dose response functions for d-methamphetamine (MA), physostigmine, atropine, and mecamylamine on force lever performance (a measure of motor control) were determined in three rhesus monkeys. The rhesus monkeys were then treated with a repeated high dose regimen of MA, and the effects of the four drugs were redetermined. Following the completion of the behavioral studies, the monkeys were killed and brain monoamine concentrations were measured. It was found that each of the four drugs produced differential effects on force lever performance indices. Following the MA regimen, the MA-treated monkeys were less sensitive to the effects of MA on force lever performance but showed no change in sensitivity to any of the cholinergic agents. The monkeys were subsequently shown to have decreased brain dopamine and serotonin levels.

Assessment of dezocine for morphine-like subjective effects and miosis

Dezocine is an analgesic soon to be marketed in the United States. In this study we examined the abuse potential of dezocine. Subjective and miotic effects of single subcutaneous doses of dezocine, morphine, and placebo were assessed under double-blind conditions in 10 adult male nondependent drug abusers. Dezocine and morphine were equipotent in inducing a constellation of effects typical of opioid agonists, including miosis and increases in opioid signs and symptoms, liking, and euphoria. Both drugs were consistently identified by subjects as being "dope" (opiates). Thus the profile of effects of single doses of dezocine indicate that the drug has the potential to be abused. However, the agonist-antagonist activities of dezocine demonstrated by others suggest that its abuse potential is less than that of morphine.

Pharmacological advances in addiction treatment

In the past 20 years significant advances in the pharmacological treatment of opioid dependence have been made, and research in this area is continuing. Therapeutic applications and current research in the use of pharmacological agents in maintenance therapy, treatment with narcotic antagonists, and narcotic detoxification are discussed. In addition, an overview is presented of recent developments in opioid pharmacology and of recently developed novel pharmacological agents which may prove useful in the future treatment and/or prevention of opioid dependence.

Diazepam and methadone interactions in methadone maintenance

Survey study data and high rates of diazepam use/abuse in methadone maintenance suggest that acute administration of diazepam with daily methadone doses may enhance methadone effects. Acute subjective and physiologic effects of single oral doses of placebo, diazepam (20 and 40 mg), methadone (100%, 150%, and 200% of the maintenance dose), and four diazepam-methadone dose combinations (20 and 40 mg diazepam in combination with 100% and 150% of the maintenance dose) were assessed under double-blind conditions. The subjects were five adult male patients on methadone maintenance with histories of diazepam abuse who were receiving 50 to 60 mg methadone a day. Physiologic measures were continuously monitored for 30 min before and for 2 hr after dosing. Pupil diameter and subjective responses were measured 15 min before dosing and 15, 30, 45, 60, 90, and 120 min after dosing. Methadone induced dose-dependent increases in pupil constriction and scores on a subjective opioid effects rating scale, but diazepam had no significant effect on either. The combination of methadone at 150% of the maintenance dose with 40 mg diazepam induced increases in these measures greater than those induced by either drug dose alone. Drug combinations, however, were more frequently identified as being benzodiazepine/barbiturate-like than as methadone-like. Thus although the subjective effects of the drug combination are distinguishable from those of methadone alone, diazepam with methadone in methadone maintenance appears to increase some physiologic and subjective opioid effects that may be related to the relatively great use/abuse of diazepam in this population.

Effects of methamphetamine on atropine-induced conditioned gustatory avoidance

The repeated administration of high doses of methamphetamine (MA) has been shown to cause monoaminergic damage in rhesus monkeys and rats. In view of the purported interaction between central cholinergic and monoaminergic systems, rhesus monkeys and rats previously exposed to high doses of MA were tested in conditioned gustatory avoidance studies with atropine (a muscarinic blocker) as the unconditioned stimulus. It was observed that both rhesus monkeys and rats previously exposed to high doses of MA exhibited less of an atropine-induced avoidance than control monkeys and rats. To control for the nonspecific effects of prior exposure to stimulants, an additional group of rats previously exposed to high doses of methylphenidate ( a stimulant shown to not cause catecholaminergic damage) was tested in the same paradigm. The methylphenidate treated rats showed no change in sensitivity to atropine in the conditioned gustatory avoidance paradigm as compared to control rats which indicated that prior exposure to the nonspecific effects of a stimulant without monoaminergic alterations does not alter the sensitivity of atropine's avoidance-inducing properties. The results of these experiments imply that atropine's avoidance-inducing properties may in part be mediated through the monoaminergic system.

A comparison of the central and peripheral effects of atropine on force lever performance

The central and peripheral effects of atropine, a muscarinic antagonist, on motor control were tested in a force lever apparatus. Three rhesus monkeys were trained to extend their arms through a tube and press a manipulandum with between 25 and 40 grams of force for 3 continuous seconds. Responding was maintained by the delivery of 1.5 ml of water. Single injections of atropine sulfate or atropine methylnitrate (a quaternary derivative) of atropine which does not cross the blood brain barrier) were given 30 min prior to the session. Atropine sulfate disrupted force lever performance in a dose related fashion. Atropine methylnitrate had little or no effect on responding. The effects of atropine on motor control as measured in this procedure, therefore, appear to be centrally mediated.

Conditioned gustatory avoidance induced by three cholinergic agents

Conditioned gustatory avoidance of sweetened condensed milk was induced in rats by drugs which differentially affect the cholinergic nervous system. After baseline water intake during a 15 minute daily session was established, sweetened condensed milk was presented in place of water, followed 15 minutes later by an IP injection of saline, physostigmine (0.5 mg/kg), atropine (25 mg/kg) or mecamylamine (25 mg/kg). Three presentations of milk were given, alternating daily with a water presentation. Atropine, a muscarinic blocker, and mecamylamine, a nicotinic blocker, both produced a strong avoidance. Physostigmine, an indirect agonist, produced a less pronounced avoidance at the dose employed. This study indicates that cholinergic agonists and antagonists are capable of inducing conditioned gustatory avoidance.

The aversive stimulus properties of repeated infusions of cocaine

When the presentation of a novel food to a rat is followed by the administration of certain compounds, including psychomotor stimulants, the animal consumes less of the food on subsequent presentations relative to an animal administered saline. This phenomenon has been termed gustatory avoidance conditioning. Conflicting results have been obtained when cocaine is used in this procedure. Therefore, the possibility that the weak efficacy of cocaine in this paradigm is due to its relatively short duration of action was investigated. Fluid intake was limited to a single 15 min presentation, seven days a week. Following the determination of baseline water in take sweetened milk was given during the session followed by a series of infusions of cocaine through chronic indwelling peritoneal catheters. Four infusions, spaced 15 min apart, of 9.0 mg/kg cocaine induced an avoidance response, while one infusion of 36 mg/kg cocaine followed by three saline infusions did not. This supports the hypothesis that the low efficacy of cocaine in this paradigm is due, at least in part, to its short duration of action.

Phencyclidine-induced stereotyped behavior in monkeys: antagonism by pimozide

The psychotomimetic substance, phencyclidine (PCP), was administered chronically to selected members of a primate social colony. PCP induced stereotyped behavior in all treated monkeys at each of three test doses. Furthermore, there was a significant increase in the amount of stereotypy seen during the second and third weeks of treatment compared to the first week. The dopamine receptor blocking agent pimozide antagonized PCP stereotypy. The results are discussed in terms of dopamine mediation of these responses.