Lisa H. Brauer

Psychopharmacological interactions between nicotine and ethanol

Epidemiological, clinical, and laboratory evidence has shown a positive correlation between cigarette smoking and ethanol use, and previous studies suggest some commonality in the neural pathways mediating effects of nicotine and ethanol. In this study, the subjective and behavioral interactions among nicotine, ethanol, and the nicotinic antagonist mecamylamine were investigated. The main objectives were to determine how the rewarding effects of nicotine might be modified by ethanol, and to compare the effects of ethanol with those of a nicotinic antagonist (mecamylamine). A total of 48 smokers who regularly consumed alcoholic beverages participated in four laboratory sessions presenting a 2 (nicotine vs. denicotinized cigarette smoke)x2 (10 mg oral mecamylamine hydrochloride vs. placebo)x2 (ethanol.5 g/kg vs. placebo) design, with ethanol as a between-subjects factor. Dependent measures included blood alcohol concentration (BAC), as assessed by breath alcohol detector; subjective drug effects; and rate of ad lib smoking during a 2-hr period. Results showed that peak BAC averaged.03 g/dl in the ethanol condition. Ethanol potentiated some of the subjective rewarding effects of nicotine, including smoking satisfaction, stimulant as well as calming effects, and relief of craving for cigarettes. During the ad lib smoking period, mecamylamine decreased satisfaction associated with the nicotine-containing cigarettes; mecamylamine also induced smoking but only in the placebo ethanol condition. These results highlight the potent interaction between ethanol and nicotinic systems, and suggest that ethanol can potentiate the rewarding effects of nicotine as well as offset some of the effects of a nicotinic antagonist.

High dose pimozide does not block amphetamine-induced euphoria in normal volunteers.

Studies with laboratory animals have shown that dopamine antagonists block the rewarding and interoceptive effects of amphetamine. However, studies using dopamine antagonists with humans have not consistently shown blockade of amphetamine-induced euphoria. The unexpected results in humans may relate to the low doses of dopamine antagonists tested. The purpose of this study was to evaluate the effects of a relatively high acute dose (8 mg) of the dopamine receptor antagonist, pimozide, on responses to d-amphetamine (10 and 20 mg) in normal volunteers. Male and female volunteers (N = 12) attended six sessions on which they received pimozide or placebo (7:30 am) followed by d-amphetamine or placebo (9:30 am). Subjective, physiological and behavioral measures were obtained at baseline (7:15 am) and hourly over a 5 h period. d-Amphetamine and pimozide, when administered alone, produced significant and opposite effects on ratings of Elation and Vigor, as well as on psychomotor performance and physiological measures. However, there were few significant interactions between pimozide and d-amphetamine. Thus, pimozide failed to consistently antagonize the effects of d-amphetamine, even at doses of pimozide that had behavioral and physiological effects when administered alone. Possible reasons for lack of robust dopamine antagonism of amphetamine-induced euphoria in humans are discussed.

Subjective responses to d-amphetamine alone and after pimozide pretreatment in normal, healthy volunteers

The role of dopamine in d-amphetamine-induced euphoria has not been systematically examined in normal volunteers. Therefore, we examined the effects of the dopamine antagonist, pimozide, on responses to d-amphetamine in healthy volunteers, using a within-subjects, double-blind design. Ten subjects received single oral doses of d-amphetamine (0, 10, 20 mg) 2 hours following pretreatment with pimozide (0, 1, 2 mg). Subjective, behavioral, and physiological effects were assessed predrug and for 3 hours after d-amphetamine administration. d-Amphetamine alone produced prototypic effects on a variety of measures, including euphoria and drug liking. Pimozide did not produce any effects when administered alone and produced inconsistent effects on responses to d-amphetamine. Although higher doses of pimozide may be needed to antagonize the euphorigenic effects of d-amphetamine, these results raise the possibility that the role of dopamine in the subjective effects of stimulants may be more complex than initially appreciated.

Inhibition of CYP2D6 activity by bupropion

Abstract: The purpose of this study was to assess the effect of bupropion on cytochrome P450 2D6 (CYP2D6) activity. Twenty-one subjects completed this repeated-measures study in which dextromethorphan (30-mg oral dose) was administered to smokers at baseline and after 17 days of treatment with either bupropion sustained-release (150 mg twice daily) or matching placebo. Subjects quit smoking 3 days before the second dextromethorphan administration. To assess CYP2D6 activity, urinary dextromethorphan/dextrorphan metabolic ratios were calculated after an 8-hour urine collection. Thirteen subjects received bupropion, and 8 received placebo. In those receiving active medication, the dextromethorphan/dextrorphan ratio increased significantly at the second assessment relative to the first (0.012 ± 0.012 vs. 0.418 ± 0.302; P < 0.0004). No such change was observed in those randomized to placebo (0.009 ± 0.010 vs. 0.017 ± 0.015; P = NS). At baseline, all subjects were phenotypically extensive CYP2D6 metabolizers (metabolic ratio <0.3); after treatment, 6 of 13 subjects receiving bupropion, but none of those receiving placebo, had metabolic ratios consistent with poor CYP2D6 metabolizers. Bupropion is therefore a potent inhibitor of CYP2D6 activity, and care should be exercised when initiating or discontinuing bupropion use in patients taking drugs metabolized by CYP2D6.

Dopamine ligands and the stimulus effects of amphetamine: animal models versus human laboratory data

Abstract Studies with laboratory animals have consistently demonstrated a role for dopamine in mediating the discriminative stimulus (i.e., interoceptive) effects of amphetamine. For example, D2 dopamine agonists mimic the discriminative stimulus effects of amphetamine and D1 and D2 dopamine antagonists generally block them. The discriminative stimulus effects of drugs in animals are believed to parallel their subjective effects in humans. Therefore, it is often assumed that dopamine plays a role in amphetamine-induced subjective effects in humans and it would be reasonable to expect that dopamine antagonists would block the subjective effects of amphetamine. Few studies have tested this hypothesis directly, and those that have have yielded inconsistent results. This paper will review data regarding the effects of dopamine agonists and antagonists on the discriminative stimulus effects of amphetamine in animals and its subjective effects in humans. Possible explanations for the discrepancies between animal and human data will be discussed, and classical assumptions underlying the use of animal models of drug effects will be examined.

Individual differences in smoking reward from de-nicotinized cigarettes

Most studies of cigarette smoking and smoking cessation have focused on the psychopharmacological effects of nicotine; relatively few have explored the role of sensory aspects of cigarette smoke. Sensory aspects of cigarette smoke play a role in the maintenance of smoking behavior, and may be particularly important for certain smokers. This paper presents the results of a pooled analysis of nine studies conducted in our laboratory, in order to explore the influence of demographic and smoking-related variables on ratings of de-nicotinized as compared to nicotine-containing cigarettes. A major finding of this analysis is that ratings of smoking derived from de-nicotinized, but not nicotine-containing, cigarettes appear to vary with level of tobacco dependence, suggesting that sensory factors may be more important to highly dependent, as compared to less-dependent, smokers. The implications of these findings for smoking cessation treatment and for future research are discussed.

Naltrexone blockade of nicotine effects in cigarette smokers

Rationale: The role of endogenous opiate systems in cigarette smoking remains unclear. In laboratory animals, opiate antagonists block many of the effects of nicotine, but in humans they do not consistently alter smoking behavior. Objective: This study explored the effects of naltrexone, alone and in combination with nicotine, on smoking behavior. Methods: In a double-blind, double-dummy, within-subjects design, 19 regular smokers received four treatments of 1 week duration: naltrexone tablet (50 mg) plus placebo skin patch, placebo tablet plus nicotine skin patch (21 mg/24 h), naltrexone tablet plus nicotine skin patch, and placebo tablet plus placebo skin patch. During each treatment, subjects rated their responses to nicotine-containing and denicotinized cigarettes in the laboratory, and to their own brand of cigarette smoked ad libitum outside the laboratory. Results: Pretreatment with the nicotine patch attenuated smoking-induced decreases in craving, negative affect, and rates of ad lib smoking, and potentiated the aversiveness of a cigarette. Naltrexone reversed these effects of the nicotine patch, and produced negative effects on mood. Conclusions: The blockade of nicotine’s effects by naltrexone supports a role for opioid mechanisms in cigarette smoking.

Evaluation of phentermine and fenfluramine, alone and in combination, in normal, healthy volunteers

Recent clinical reports indicate that combined administration of phentermine and fenfluramine may have useful effects in the treatment of drug abuse. The present study was designed to evaluate the subjective and mood-altering effects of these drugs, alone and in combination, in normal healthy volunteers. Seven male and five female volunteers participated in an eight-session, double-blind study in which each subject received each of the following drug conditions: d-amphetamine (10 and 20 mg), phentermine (30 mg), fenfluramine (40 and 80 mg), phentermine (30 mg) with fenfluramine (40 mg), phentermine (30 mg) with fenfluramine (80 mg), and placebo. Sessions were conducted in a laboratory setting two or three days a week. Subjects completed standardized self-report questionnaires and psychomotor tests before and at regular intervals after each drug administration. Phentermine produced effects that were similar to those of d-amphetamine, whereas fenfluramine produced different and apparently aversive effects (e.g., it increased measures of anxiety and confusion). Phentermine reduced the apparently aversive effects of fenfluramine when the two drugs were given together. These results suggest that the combination of phentermine and fenfluramine would have a low potential for abuse.

Smoking topography in tobacco chippers and dependent smokers.

Although most cigarette smokers exhibit signs of tobacco dependence, a subset of this population, referred to as tobacco chippers, does not show characteristic signs of dependence. Few studies have attempted to characterize differences between these groups of smokers. The purpose of the present study was to examine smoking topography in chippers (CH) and dependent smokers (DS). Topographical variables including puff number and duration, and intercigarette interval were examined in seven CH and seven DS under both laboratory and naturalistic conditions. Saliva nicotine, cotinine, and thiocyanate, as well as expired air carbon monoxide (CO) levels were also measured. The results indicate that there were no differences in smoking topography between CH and DS, except those that would be expected based on selection criteria. Although there were differences between groups on pre- and postsmoking CO and saliva cotinine levels, there were no differences in change scores from pre- to postsmoking on these measures. Additional studies will need to be done in order to completely characterize differences between CH and DS.

EFFECTS OF CARBAMAZEPINE ON ACUTE RESPONSES TO SMOKED COCAINE-BASE IN HUMAN COCAINE USERS

A double-blind, placebo-controlled cross-over study was conducted to determine the effects of carbamazepine on the acute physiological and subjective responses to a single dose of smoked cocaine-base. Male cocaine users (N=6) were given 400 mg carbamazepine or placebo, each for a period of 5 days. At the end of the 5-day period, a 40 mg dose of smoked cocaine was administered. The results showed a significantly higher heart rate, diastolic blood pressure elevation, and blood pressure-heart rate product under the carbamazepine compared to the placebo condition. There were no effects of carbamazepine on the subjective responses from cocaine. The increase in cardiovascular functions indicates a need to be cautious in the use of carbamazepine in the treatment of cocaine abusers.