Effects of Vigabatrin on Cocaine Self-Administration

The objective of this study is to determine if vigabatrin will decrease cocaine self-administration, cardiovascular effects, subjective effects and craving compared to placebo.

Two recent open label clinical trials have reported that the anticonvulsant, gamma vinyl-GABA (GVG; vigabatrin), decreases relapse to cocaine use (Brodie et al., 2003, 2005). Vigabatrin increases neural GABA levels by irreversibly inhibiting the primary GABA degradation enzyme, GABA-transaminase; the hypothesized mechanism by which vigabatrin decreases cocaine relapse is by increasing GABA levels, thereby decreasing the effects of cocaine and cocaine-associated environmental cues on extracellular dopamine concentrations in the mesolimbic dopaminergic pathway (Morgan and Dewey, 1998). We are proposing to use our model of repeated dose cocaine self-administration to assess the interaction between vigabatrin and smoked cocaine under controlled laboratory conditions. This 57-day outpatient/inpatient /outpatient/inpatient protocol will evaluate the effects of vigabatrin maintenance (0, 3 g/day) on cocaine craving, subjective effects, and self-administration using a within-subjects design. Non-treatment seeking cocaine-dependent volunteers will be maintained outpatient for 14 days of vigabatrin maintenance prior to beginning each inpatient study phase. 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 purchase doses of smoked cocaine (0, 12, 25, 50 mg; $5/administration). In addition to measuring cocaine self-administration, we will measure the cardiovascular and subjective effects of repeated cocaine administration and cocaine craving under each vigabatrin maintenance condition. Determining vigabatrin's effects on a range of smoked cocaine doses will provide essential data on the mechanism of the vigabatrin-cocaine interaction.

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 Agrees to practice an effective form of contraception Exclusion Criteria: Current seizure disorder or heart disease Currently meeting DSM-IV criteria for all major psychiatric/psychotic disorders. Volunteers with a history of depression or psychosis will also be excluded (p. 43, Investigator's brochure) Dependence on substances other than cocaine or nicotine Request for drug treatment Judged to be noncompliant with study protocol Clinical laboratory tests outside normal limits that are unacceptable to the study physician (e.g., BP > 140/90; BUN, creatinine, LFTs > 1.5 ULN; hematocrit < 34 for women, < 36 for men; pseudocholinesterase deficiency) Current parole or probation Recent history of significant violent or suicidal behavior Pregnancy or lactation Baseline visual field defects