Psychopharmacology for Cocaine Dependence - Buspirone

The University of Texas Health Science Center, Houston50 enrolled

Overview

Chronic cocaine use may produce disruption of neurotransmitter functions (including dopamine). This may in turn contribute to measurable dysfunction in important cognitive and behavioral processes. Stimulants that enhance dopamine (DA) function may help in treating cocaine dependence and improving behavioral function -- supporting the notion that these processes are related. An important step is to understand the subjective, physiological, and behavioral effects of potential medications for cocaine dependence. DA-modulating drugs may be targets for pharmacotherapy for substance dependence, and particularly for stimulant drugs like cocaine, which disrupt normal DA function. Buspirone is currently the only available dopamine subtype 3 (DA3) approved for human administration, and is thus a viable investigational compound. This project proposes to evaluate the DA-modulating effects of buspirone on behavioral deficiencies related to DA depletion. Accordingly, the project aims to characterize the effects of buspirone in individuals with cocaine dependence. Employing a daily dosing designs within an acute stimulant challenge (methylphenidate), the experiment will characterize the subjective effects, cardiovascular effects, and behavioral effects (attentional bias to drug cues and risky decision making). The primary hypotheses are that buspirone will attenuate the increases in subjective drug effects ("stimulated", "like drug") and behavioral effects (increases in attentional bias and risky decision making) that are produced by acute methylphenidate administration.

Chronic cocaine use may produce disruption of monoamine systems (including dopamine). This may in turn contribute to measurable dysfunction in important cognitive and behavioral processes. Pharmacotherapy with stimulants that enhance dopamine (DA) function has shown efficacy in treating cocaine dependence and improving behavioral function -- supporting the notion that these processes are related. In the development of novel pharmacotherapies for cocaine dependence, an important step is a full characterization of the psychopharmacological properties of potential medications for cocaine dependence, including subjective, physiological, and behavioral effects. Selective medications may play a key role in the modulation of DA neurotransmission by enhancing DA receptor activation. The D3 receptor is an autoreceptor that may function to control phasic DA activity and mediate sensitization of DA agonists, thus playing a role in conditioning of drugs of abuse like cocaine. Growing evidence suggests that D3 receptor antagonists may be targets for pharmacotherapy for substance dependence, and particularly for stimulant drugs like cocaine, which disrupt normal DA function. Importantly, administration of D3 antagonists may disrupt reactivity (attention) to drug cues and attenuate cue-induced craving. Buspirone is currently the only available D3 antagonist approved for human administration, and is thus a viable investigational compound. This project proposes to evaluate the potential pharmacotherapeutic action of the D3 antagonist buspirone. The DA-modulating effects of buspirone may help with affective and behavioral deficiencies related to DA depletion. Accordingly, the project aims to characterize the psychopharmacology of buspirone in individuals with cocaine dependence. Employing chronic dosing designs within an acute stimulant challenge (methylphenidate), the experiment will be conducted using well-established psychopharmacological methods in order to characterize the shape and magnitude of chronic pretreatment-mediated change in the methylphenidate dose-response curve. Measures will include subjective effects, cardiovascular effects, and behavioral effects (attentional bias to drug cues and risky decision making). These data will compliment and provide valuable information to clinical trials using these agents to treat cocaine dependence.

Interventions

BuspironeDRUG

\[week 1: Buspirone 30 mg twice a day (9am and 6pm) on Monday through Sunday\] \[weeks 2-3: Buspirone 45 mg twice a day (9am and 6pm) on Monday through Sunday\]

Placebo for BuspironeDRUG

\[week 1: Placebo for Buspirone twice a day (9am and 6pm) on Monday through Sunday\] \[weeks 2-3: Placebo for Buspirone twice a day (9am and 6pm) on Monday through Sunday\]

MethylphenidateDRUG

Methylphenidate serves as an acute stimulant challenge. \[week 1: no Methylphenidate or Methylphenidate placebo\] \[week 2: 0mg Methylphenidate (placebo for Methylphenidate) on Monday at 10am; Methylphenidate once a day (10am) on Wednesday and Friday, and on each of these 2 days the Methylphenidate dose will be different (15 mg, 30mg, 60 mg, or 0mg)\] \[week 3: Methylphenidate once a day (10am) on Monday and Wednesday, and on each of these 2 days the Methylphenidate dose will be different (15 mg, 30mg, 60 mg, or 0mg)\]

Placebo for MethylphenidateDRUG

\[week 1: no Methylphenidate or Methylphenidate placebo\] \[week 2: 0mg Methylphenidate (placebo for Methylphenidate) on Monday at 10am; Methylphenidate once a day (10am) on Wednesday and Friday, and on each of these 2 days the Methylphenidate dose will be different (15 mg, 30mg, 60 mg, or 0mg)\] \[week 3: Methylphenidate once a day (10am) on Monday and Wednesday, and on each of these 2 days the Methylphenidate dose will be different (15 mg, 30mg, 60 mg, or 0mg)\]

Eligibility

Sex: ALLMin age: 18 YearsMax age: 60 Years

Medical Language ↔ Plain English

Inclusion Criteria: * cocaine dependent subjects, non-treatment seeking * meet current DSM-IV criteria for cocaine dependence disorder * report using cocaine within the past 30 days * at least 1 positive urine toxicology screen for the cocaine metabolite benzoylecgonine (BE) \[300 ng/mL, during the initial (2-4 day) screening period * acceptable health on the basis of interview, medical history, and physical exam * able to understand the consent form and provide written informed consent. Exclusion Criteria: * currently dependent on any psychoactive substance other than cocaine or nicotine * current DSM-IV diagnosed major psychiatric disorder (e.g., psychosis, bipolar, major depressive disorder) * any medical condition that would contraindicate administration of medications * taking medications known to have significant drug interactions study medications * probation / parole requiring reports of drug use to court officers * pregnant or nursing for female patients * cannot read, write, or speak English.

Outcomes

Primary Outcomes

Attentional Bias as Assessed by Score on the Stroop Task

The mean score over all 4 time points is reported in this outcome measure (i.e., a summary score is reported). Each subject contributed 1 data point for each dose level of Methylphenidate (15mg, 30mg, 60mg, or 0mg), resulting in a total of 20 data points per dose level per arm. The Stroop task assesses attentional biases to cocaine-related (drug-related) and rewarding (non-drug related) stimuli vs. neutral stimuli. Participants are instructed to respond to words shown in different colors on the screen, by pressing as quickly and accurately as possible on one of three colored buttons. Attentional bias is measured as the difference in reaction times on cocaine vs. neutral words. The reported score is a difference score in milliseconds (cocaine minus neutral), in which positive means slower to respond to cocaine and thus greater attentional bias, and negative means no attentional bias to cocaine words.

Time frame: 1 time a day on Wednesday and Friday of week 2; 1 time a day on Monday and Wednesday of week 3

Risky Decision Making as Assessed by Score on the Risky Decision Making Task

The mean score over all 4 time points is reported in this outcome measure (i.e., a summary score is reported). Each subject contributed 1 data point for each dose level of Methylphenidate (15mg, 30mg, 60mg, or 0mg), resulting in a total of 20 data points per dose level per arm. The risky decision making task provides subjects with three choice options on each of 100 repeated trials. Options are low, moderate, and high risk, based on variance and probability in gain/loss amounts. The low risk option is more adaptive over many trials. The outcome measure is a risk index (ranging from 0.33 to 100) that factors in tolerance for variability and amount of gains and losses across the three options. 100 is highest risk. 0.33 is lowest risk.

Time frame: 1 time a day on Wednesday and Friday of week 2; 1 time a day on Monday and Wednesday of week 3

Secondary Outcomes

Subjective Effects as Assessed by the Addiction Research Center Inventory (ARCI)

The ARCI short form will be used. It is a 49-item true / false questionnaire that has been empirically-derived to assess five different factors, including euphoria, sedation, and dysphoria. The PCAG scale has proven to be a sensitive measure of subjective effects in many studies administering stimulant drugs.