Unlike opiates such as heroin or prescription painkillers, there is no medication specifically approved to help curb cocaine consumption. Now, an experimental vaccine offers hope for a new approach, researchers say, that spurs on antibodies, which bind with cocaine molecules and apparently helps some addicts stop feeling the pleasurable effects of the drug—thus deconditioning them out of their dependency.
Cocaine, both inhaled powder form and smoked "crack" cocaine, accounts for about one in three drug-related emergency room admissions, according to the U.S. Department of Health and Human Services. And it has about 1.4 million users in the U.S., Nora Volkow, director of the National Institute on Drug Abuse (NIDA), said in a press briefing held today to announce the vaccine findings. Developing a simple vaccine to help addicts stop taking the drug would be a large step in decreasing the overall number of people who use it, many of whom, Volkow noted, are between the ages of 18 and 25.
The vaccine itself does not destroy cocaine molecules, rather it induces antibodies that bind to it, making the stimulant lose its ability to pass through the blood–brain barrier—and thus unable to trigger a high.*
To test the vaccine's effectiveness in humans, researchers (with some help and financial backing from Celtic Pharma) enlisted 94 subjects who had enrolled in a methadone treatment program for opiate addiction—and who also regularly used cocaine—for a placebo-controlled, double-blind study. (They decided on this group because methadone programs historically have better retention rates than programs for cocaine abuse only.) One group received a placebo, another a low dosage of vaccine, whereas a third was administered a high dosage over a series of 12 weeks with five total injections.
More than half of the subjects in the high-dosage group (53 percent) appeared to have laid off the cocaine for more than half of the trial period, the researchers report after tracking traces of the drug in urine samples collected three times a week. Just less than a quarter of subjects with the low dosage had the same track record, according to the results published online yesterday in the Archives of General Psychiatry. A drop in cocaine usage across all groups may also be attributed to a curb in opiate drug consumption from the methadone treatment.
Despite the overall decrease in cocaine use, only 38 percent of the subjects taking the high levels of vaccine achieved sufficient levels of antibodies to prevent the absorption of cocaine into the brain. And of this minority, the functional levels of antibodies were present starting only after two months from the first vaccine and were in decline 16 to 24 weeks into the trial.
Thomas Kosten, a professor in the Menninger Department of Psychiatry and Behavioral Sciences at the Baylor College of Medicine in Houston and a lead study author, is confident that with better vaccine ingredients (theirs used a traditional cholera toxin strengthened with an aluminum hydroxide adjuvant), the vaccine's effectiveness could be improved to as high as 80 percent. In animal trials, he noted, with newer vaccines donated from pharmaceutical companies the researchers found more than four times the amount of antibodies in the rats.
Although the vaccine lessened or negated participants' ability to feel high from the drug, many of the trial participants still consumed cocaine—and at levels far higher than normal. Such so-called "testing," as Kosten noted in the press briefing, was expected and is seen in animal experiments, as well. And even after having warned trial volunteers about the potential dangers of challenging the dosage limits when they couldn't reach an expected high, some showed as much as 10 times the habitual amount of cocaine in their urine until, he said, they likely just ran out of money.
The search for a cocaine vaccine has also revealed that some individuals "seem to be immune to immunization," Kosten said. Like acclimation to a former allergen, he explained, it is possible for "your body [to] think that it's a part of you," and to not allow antibodies to bind to the cocaine molecule. This may be more common, he speculates in those who have had lung tissue damage from the drug—akin to an allergist repeatedly scratching the skin to introduce an allergen.
The new findings, which Volkow called "transformative" in the briefing, may ultimately be translatable to other addictive substances, and may pave the way to creating anti-addiction vaccines for other drugs. "We're very enthusiastic about this," Kosten said about this prospect. He notes that alcohol, however, with a much smaller molecule than other drugs, may prove to be too diminutive for a similar antibody-based approach.
Aside from improving the current vaccine technology, Kosten said, one of the big challenges will be enlisting the help of what he called "Big Pharma." The large pharmaceutical companies are becoming more involved in developing similar technology for nicotine addiction, but, Kosten noted, they must be persuaded to investigate treatment for illicit drug addiction, "which just doesn't have the profit margin that nicotine does."
*Note (10/7/09): Due to an error, this sentence has been modified since the original posting.