Effects of Aripiprazole on Cocaine Craving and Self-Administration

The purpose of this study is to investigate whether aripiprazole will decrease cocaine self-administration, subjective effects and cravings compared to placebo.

Despite the recent increase in data about cocaine's basic neurochemical mechanisms of action, progress towards the development of an effective pharmacological treatment for cocaine abuse has been disappointing. We are proposing to use our laboratory model of repeated dose cocaine self-administration to assess the potential efficacy of the novel antipsychotic, aripiprazole. Aripiprazole is a partial agonist at both the dopamine D2 receptor and at the serotonin 5HT1a receptor, while antagonizing the 5HT2a receptor. By functioning as a partial D2 agonist, aripiprazole is hypothesized to function as a D2 antagonist during hypodopaminergic states, such as during cocaine use, while functioning as a D2 agonist during hypodopaminergic states, such as during cocaine withdrawal. This 42-day, outpatient/inpatient/outpatient/inpatient protocol will evaluate the effects of aripiprazole maintenance (0, 15 mg/day) on cocaine craving, subjective effects, and self-administration using a within-subjects design. Non-treatment seeking cocaine abusers will be maintained outpatient for 16 days of dose maintenance prior to inpatient cocaine self-administration sessions. During the inpatient phases, volunteers will live on a hospital clinical research unit and will participate in laboratory sessions in which they will have the opportunity to choose between repeated doses of smoked cocaine and $5. In addition to measuring their cocaine self-administration, we will measure the cardiovascular and subjective effects of cocaine under each aripiprazole maintenance condition.

In order to achieve steady-state concentrations, participants (n=8 men) were administered placebo and aripiprazole (15 mg/day) capsules in counter-balanced order for 21 days. A smoked cocaine dose-response curve (0, 12, 25, 50 mg) was determined twice under placebo and aripiprazole maintenance.

Aripiprazole (15 mg/day) in conjunction with a smoked cocaine dose-response curve (0, 12, 25, 50 mg).

Participants received aripiprazole (15mg/day) in conjunction with a dose-response of cocaine (0, 12, 25, 50 mg).

Mean number of cocaine choices as a function of cocaine dose and aripiprazole dose (n=8). Participants sampled the dose of cocaine available for the session and then had five choices to respond for money ($5.00) or cocaine using a modified progressive-ratio schedule.

Mean Visual Analog Scale (VAS) ratings (items: "Quality", "Pay for Dose", "Good Drug Effect", and "Cocaine Craving") from 0-100mm as a function of cocaine dose and aripiprazole dose 4 min following a single administration of cocaine (the "sample dose") at the start of the session. For "Quality" item, the perceived quality of the drug is rated. The higher the rating, the better quality the drug was perceived to be. For "Pay for Dose" item, the likelihood that the participant would pay for the drug is indicated. Higher ratings indicate a better likelihood that the person would pay for the dose received. For "Good Drug Effect", the likelihood of feeling a good drug effect is indicated. The higher the number, the more of a good drug effect the person reported. For "Cocaine Craving", the intensity of craving is reported. Higher scores indicate more craving for cocaine.

Mean plasma cocaine levels after a single administration of each cocaine dose as a function of aripiprazole and cocaine dose.

Inclusion Criteria: Meets DSM-IV criteria for current cocaine abuse Average use of smoked cocaine is at least 2x/week for past 6 mos); currently spends at least $70 per week on cocaine Has patterns of smoked cocaine use in terms of frequency and amounts which parallel or exceed those administered in the study Age 21-45 Able to give informed consent, and comply with study procedures Exclusion Criteria: Current seizure disorder, heart disease or psychiatric disorders (other than cocaine dependence) Dependence on substances other than cocaine or nicotine Request for drug treatment Judged to be noncompliant with study protocol Current use of any medication that has the potential to interact with aripiprazole (i.e., seizure medications, anti-fungal medications, cardiac medications, or medication that produces drowsiness) Clinical laboratory tests outside normal limits that are clinically unacceptable to the study physician (BP > 140/90; BUN, creatinine, LFTs > 1.5 ULN; hematocrit < 34 for women, < 36 for men; pseudocholinesterase deficiency) Currently meeting DSM-IV criteria for all major psychiatric/psychotic disorders other than transient psychosis due to drug abuse Current parole or probation History of significant violent or suicidal behavior