Vaccine for Cocaine Addiction Shows Promise

The use of a new vaccine designed to help those who are addicted to cocaine has achieved limited success in the battle to beat the habit. Although the vaccine is not a cure, the results of a recent study have revealed that it shows promise for future treatment of the addiction.

During the trial, led by Dr. Bridget A. Martell, of Yale University School of Medicine, New Haven, and Veterans Affairs Connecticut Healthcare System, West Haven, just over one-third of participants developed immune system antibodies to cocaine, leading to a decrease in their use of the drug. However, the positive effects were short-lived, as they were only sustained for two months. The study was recently published in the Archives of General Psychiatry.

The trial included 115 adult users of crack cocaine who were between the ages of 18 and 46, and who were involved in methadone maintenance programs for opioid addiction. Of these, a total of 94 participants completed the study. The subjects were randomly assigned to receive five shots of either the vaccine or a placebo, and the researchers tested their urine three times weekly for cocaine use over 24 weeks.

Findings showed that 38 percent of the 55 participants who received the cocaine vaccine achieved desired cocaine antibody levels of 43 micrograms per milliliter or higher. Of these, more had cocaine-free urine samples between weeks 9 and 16 of the study period than either participants with antibody levels falling below target or those who received the placebo.

Results also revealed that 53 percent of participants who attained high antibody levels were able to reduce their cocaine use by half in comparison to only 23 percent of those who developed low antibody levels. However, the encouraging results observed among participants receiving the vaccine did not last. A sharp decline in positive effects of the vaccine was noted after week 16 and onward to the end of the trial period at week 24. Martell and her colleagues say that repeated booster vaccinations are likely to be necessary to achieve optimal treatment results, as the antibody levels are raised slowly.

The vaccine works by helping the immune system recognize cocaine as a foreign substance. Cocaine is made up of tiny molecules that can cross the body’s blood-brain barrier without immediate detection by immune system. The vaccine attaches cocaine-like molecules to a larger protein that allows the immune system to detect both the protein and its cargo. With the use of repeated injections, a sufficient level of antibodies can be created that will disable the drug prior to its entry into the brain, and prevent the euphoria and triggering of brain chemicals that lead to drug cravings.

Dr. Thomas Kosten, a psychiatrist at Baylor College of Medicine and co-author of the study, explained, “The antibodies slow cocaine’s entry into the brain. And because it is slowed down so much, the drug isn’t reinforcing any more.” He further noted, “The most promising thing we found is that once we got those cocaine antibody levels up, they were more effective than we thought they were going to be. The part that we did expect, but that was still disappointing, is about 20 percent of people don't make much of an antibody response.” Kosten also acknowledge that another study on the vaccine will begin in January, and will enroll about 300 cocaine-dependent individuals.