The antiepileptic agent vigabatrin (gamma-vinyl gamma-amino butyric acid [gamma-vinyl GABA]) shows great promise for people with long-term addiction to cocaine, methamphetamine, or both, according to an article published online November 18th by Synapse. The results from this second, small trial confirm findings from an earlier study and will be published in the February 2005 print issue of Synapse.

The current study, which involved 30 people, was conducted at a national addiction treatment center in Mexico by a team led by Jonathan Brodie, MD, PhD, the study’s lead author, and Stephen Dewey, PhD. No visual side effects were found in any of the patients.

"The fact that this drug appears to be effective in treating addiction to both cocaine and methamphetamine is particularly promising, given that methamphetamine abuse is one of the fastest growing drug problems in this country," said Brodie.

"We are unaware of any pharmacologic strategy that has been useful in treating methamphetamine dependence, making these findings with vigabatrin [abbreviated as GVG] unique both in terms of safety and efficacy," added Brodie. "We expect that the small clinical trials of GVG will lead to larger, placebo-controlled studies of this promising treatment."

Dewey and Brodie have conducted extensive brain-imaging and behavioral studies on animals showing that GVG attenuates and, in some cases, blocks neurological and behavioral changes associated with drug addiction. In late 2003, Brodie and Dewey published results from the first small-scale human clinical trial of GVG to assess its effects on drug abusers; they found that the drug can block cocaine craving in addicts.

GVG is approved for the treatment of epilepsy in many countries, including Mexico, but it is not approved for any indication in the United States, in part because some epilepsy patients who took cumulative doses in excess of 1500 grams experienced a reduction in their field of vision. The current study was designed to look for such visual side effects while testing the efficacy of a relatively low GVG dose.

In response to word-of-mouth and newspaper-ad recruitment, 30 patients enrolled in the study. All had abused methamphetamine and/or cocaine daily for a mean duration of 12 years. The experimental design was "open-label," that is, the subjects knew they were getting GVG, an experimental treatment for drug addiction.

Of the 30 volunteers, 18 stayed in the study for the nine-week duration. Of those, 16 were methamphetamine- and cocaine-free for more than four consecutive weeks while two continued using but in reduced amounts. Of the 16, 12 remained free of methamphetamine and cocaine through the end of the study. No subject, whether they completed the trial or not, developed defects in visual fields or acuity.

"Due to the open-label nature of this study and the lack of a control group, we cannot conclude that these subjects' ability to abstain from drug use was a direct result of being given GVG," said Dewey. "However, in a group of heavy users where none had stayed 'clean' for more than several consecutive days in the past year, it is remarkable that 16 of 30 avoided using these highly addictive drugs for approximately four consecutive weeks while on GVG."

"Of course, the conclusive demonstration of treatment efficacy can only be provided by an appropriately blinded randomized study, where some patients are given GVG and others a placebo, and neither the researchers nor the subjects know which is which until after the results are analyzed," noted Brodie.

With the lack of visual side effects observed for the doses used in this study - a factor that has been viewed as an impediment to getting GVG approved in the United States - the scientists hope to see a large-scale study conducted soon.