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A vaccine against cocaine was effective in nearly 40% of users of the drug, researchers said.
In a randomized, placebo-controlled study, volunteers who reached a high level of antibodies after vaccination used less cocaine than those whose response was lower, according to Thomas Kosten, MD, of Baylor College of Medicine in Houston and colleagues.
But as the effect of the vaccine wore off, antibody levels fell and many volunteers returned to abusing the drug, Kosten and colleagues said in the October issue of Archives of General Psychiatry.
"We didn't expect to cure them in six months," Kosten said, "and we didn't."
But he said that other studies have shown that a booster shot every two months can keep antibody levels high enough to block the euphoric effects of cocaine.
"In clinical practice, you'd probably give people a booster shot every two months," he said, which, compared with some long-term treatments, is "pretty easy to provide."
That, he said, might allow enough time off the drug to let psychosocial forms of treatment have an effect.
Kosten and colleagues tested a vaccine in which succinylnorcocaine was linked to recombinant cholera toxin B-subunit protein.
The idea is to tie up cocaine molecules in the blood where they can be degraded by enzymes. That delay ensures that less of the drug reaches the brain and the euphoric effect is muted or nonexistent.
Indeed, Kosten said, some vaccinated volunteers said they tried larger than normal doses of the drug during the study and reported no effect.
Cocaine-using volunteers, all enrolled in a methadone program for opiate abuse, were randomized to get five shots of vaccine or placebo over a 12-week period. They were followed for an additional 12 weeks.
Based on animal studies, the researchers expected that volunteers who reached serum IgG anticocaine antibody levels of 43 micrograms per milliliter or higher would use less cocaine than those who didn't make as much antibody or who got placebo.
To measure that, the researchers performed urine tests for cocaine metabolites three times a week.
- 38% of the vaccinated volunteers -- 21 of 55 -- reached the 43-microgram level.
- During weeks nine through 16 of the study -- when antibody levels were expected to be at their peak -- those volunteers had cocaine-free urine tests 45% of the time.
- In contrast, those with lower levels of antibodies and those getting placebo were cocaine-free only 35% of the time.
- The difference was significant at P<0.03.
- All volunteers reduced cocaine use during the study, but those with high levels of antibody had a significantly greater decrease (at P<0.001) during weeks nine through 16.
- During the remaining weeks of the study, as antibody levels fell, there was no significant difference among the groups.
Adverse effects of the vaccine were limited to redness and soreness at the injection site.
A major hurdle, Kosten said, is to find a pharmaceutical company that's willing to develop a cocaine vaccine.
In the meantime, there are no approved pharmacologic approaches to cocaine addiction, he said, and even a treatment that would work for 38% of addicts would be "damn good."
"Overall, this vaccine -- even as it is -- would probably do pretty well with people who have already stopped using cocaine and just want to keep themselves from relapsing back," he said.
The study was supported by the National Institute on Drug Abuse and by the Veterans Affairs Mental Illness Research, Education, and Clinical Center. Celtic Pharmaceuticals supplied the succinylnorcocaine-recombinant cholera toxin B-subunit vaccine.
Kosten reported travel fees for consultative services from Celtic but made no other financial disclosures.