Safety and Efficacy Study of Vigabatrin to Treat Methamphetamine Dependence

The objective of this study is to demonstrate that a larger proportion of vigabatrin-treated subjects than placebo-treated subjects will be methamphetamine-free in the last 2 weeks of the study's Treatment Phase (Weeks 11 and 12).

This is a Phase II, randomized, double-blind, placebo-controlled, intent-to-treat, 2-arm, parallel design, multicenter study to evaluate vigabatrin as a treatment for methamphetamine addiction. The study will involve approximately 180 subjects (90/group) who meet DSM IV criteria for methamphetamine dependence. Subjects will be evaluated for their compliance with protocol inclusion/exclusion criteria during Screening/Baseline Phase, lasting up to 4 weeks.

At the conclusion of the Screening/Baseline Phase, subjects meeting all inclusion/exclusion criteria will be randomized to one of two treatment groups: vigabatrin or placebo. Subjects will proceed to a 12 week Treatment Phase and then undergo a 12 week follow-up period. Subjects will be scheduled for clinic visits 3 times per week for efficacy and/or safety assessments during the Screening/Baseline Phase and the 12 week Treatment Phase. Subjects will return for follow up visits at Weeks 13, 16, 20 and 24.

Eligibility Criteria:
Inclusion Criteria:

Able to understand the study and provide written informed consent.

* Male or female at least 18 years of age.
* Meets DSM-IV (Diagnostic and Statistical Manual of Mental Disorders Fourth Edition) criteria for methamphetamine dependence as major diagnosis, as determined by the Substance Abuse module of SCID (Structured Clinical Interview for DSM-IV).
* Provides at least one urine specimen which is positive for methamphetamine according to a rapid screening test.
* Seeking treatment for methamphetamine dependence.
* Have normal visual fields.
* Be in generally good health based on history, physical examination and laboratory findings.
* If female of childbearing potential, use acceptable contraceptive methods

Exclusion Criteria:

* Has current dependence on any psychoactive substance other than methamphetamine, alcohol, nicotine, or cannabinoid or physiologic dependence on alcohol requiring medical detoxification.
* Has any serious medical or psychiatric illness and/or clinically significant abnormal laboratory values.
* Has history of serious cardiovascular reaction to methamphetamine.
* Has clinically significant cardiovascular impairment, abnormal ECG or uncontrolled hypertension.
* Be under court or other governmental agency (e.g. social services) mandate to obtain treatment or requiring outside urine monitoring.
* Be enrolled in an opiate substitution treatment program within 2 months of randomization.
* Has ever taken vigabatrin in the past.
* Is pregnant or lactating.
* Has clinically significant ophthalmologic disease, which would preclude safety monitoring, is undergoing treatment for ocular disease or intends to have any ocular surgery or procedure performed during the time of their participation in the trial.
* Has received a drug with known major organ toxicity, including retinotoxicity.
* Is currently participating in, or has been enrolled in another clinical trial within the last 30 days.
* Be anyone who, in the judgment of the investigator, would not be expected to attend regular study visits or to complete the study protocol.