The experimental cocaine vaccine works by raising levels of cocaine antibodies to hamper the drug's ability to affect the brain.
Researchers found that treated drug users who responded well to the vaccine by achieving high antibody levels were twice as likely to reduce their cocaine use by half and had more cocaine-free urine tests than those with low antibody levels or who received a placebo vaccine.
However, only about a third (38%) of those treated with the cocaine vaccine achieved those high antibody levels, and those who did maintained them for only two months.
Researchers say more study is needed to increase the proportion of users who achieve the desired antibody levels and to maintain those levels long enough to treat the cocaine addiction.
About 2.5 million Americans were dependent on cocaine or addicted in 2007, but researchers say only about 809,000 received treatment. Cocaine use also accounts for one in three drug-related emergency room visits.
There is no FDA-approved drug to help treat cocaine addiction and behavioral therapies have varying levels of success. But researchers say animal studies have suggested that raising levels of anti-cocaine antibodies can capture cocaine in the body, hindering its delivery to the brain to reduce cocaine-induced euphoria without causing any significant psychological side effects or drug interactions.
The study, published in the Archives of General Psychiatry, evaluated the effectiveness of an experimental cocaine vaccine in 94 cocaine-using adults over 24 weeks.
About half were randomly assigned to receive five doses of the cocaine vaccine, and the others received placebo injections. Researchers tested the participants' urine three times a week for cocaine use.
Of the 55 participants who received all five doses of the cocaine vaccine, 38% achieved cocaine antibody levels of 43 micrograms per milliliter or higher. Those who did had more cocaine-free urine samples between weeks nine and 16 of the study than those with lower antibody levels or who received the placebo.
In addition, 53% of those with high antibody levels reduced their cocaine use by half compared with 23% of those with low antibody levels. The most frequently reported side effects for the vaccine-treated group were tenderness and firmness at the injection site, feeling cold, hot flashes, nausea, and increased sweating.
Researcher Bridget A. Martel, MD, of the Yale University School of Medicine in New Haven, Conn., and colleagues say repeated booster vaccinations will likely be required to achieve optimal treatment as well as increased efforts to help retain users during the initial phase of injections since antibody levels rise slowly.