A vaccine to treat cocaine dependence appears to reduce use of the drug in a subgroup of individuals who attain high anticocaine antibody levels in response, according to a report in the October issue of Archives of General Psychiatry, one of the JAMA/Archives journals. However, only 38 percent of vaccinated individuals produced high enough antibody levels and those who did maintained them for only two months.
About 2.5 million Americans are dependent on cocaine, but only 809,000 receive treatment, according to background information in the article. One of every three drug-related emergency department visits can be attributed to cocaine dependence, which also has substantial social and economic effects. The U.S. Food and Drug Administration has not approved any pharmacological therapies for cocaine abuse, and behavioral therapies have a wide range of effectiveness. Animal and human studies have suggested that high levels of anticocaine antibodies in the blood can sequester and inactivate cocaine before it enters the brain, reducing feelings of euphoria from the drug without causing any psychoactive effects or harmful interactions.
Bridget A. Martell, M.D., M.A., of Yale University School of Medicine, New Haven, and Veterans Affairs Connecticut Healthcare System, West Haven, and colleagues conducted a 24-week phase 2b trial of a vaccine designed to increase levels of cocaine antibodies in the blood. A total of 115 cocaine-dependent individuals enrolled and 58 were randomly assigned to receive five vaccinations of the active vaccine. The other 57 received placebo injections over 12 weeks. In both groups combined, 94 (82 percent) completed the trial. Three times per week for 24 weeks, participants' urine was tested for metabolized cocaine.
Of the 55 participants who completed five active vaccinations, 21 (38 percent) attained blood cocaine antibody levels of 43 micrograms per milliliter or higher; those who did had significantly more cocaine-free urine samples between weeks nine and 16 of the study than individuals who did not attain those antibody levels or who received placebo injections (45 percent vs. 35 percent cocaine-free urine samples). The proportion of participants who reduced their cocaine by half was also greater in the group with high antibody levels than in those with a low antibody level (53 percent vs. 23 percent).
Adverse events associated with the vaccine were mild or moderate, with the most frequent being hardening and tenderness at the injection site. No treatment-related serious adverse events, withdrawals or deaths occurred.
"Optimal treatment will likely require repeated booster vaccinations to maintain appropriate antibody levels. Furthermore, efforts will be needed to retain subjects during the initial series of injections since antibody levels increased slowly over the first three months when patients were immunized according to the protocol used in these studies," the authors write. "Other treatments need to be used during this early treatment period to encourage abstinence. As an example, to retain subjects in this study during the initial slow increase in antibody responses, we enlisted cocaine-dependent subjects who were enrolled in a methadone maintenance program."
"Thus, the goals for future vaccine development will be to increase the proportion of subjects who can attain the desired antibody levels and to extend these periods of abstinence through long-term maintenance of these adequate antibody levels," they conclude. "We look forward to extending our promising findings in a broader population of cocaine abusers as we also reach for these future vaccine development goals."
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