A vaccine designed to help cocaine users shake free of the drug failed to meet its primary objective in a Phase II trial, but the results still provide signs that it could be an effective treatment for the addiction.

The TA-CD vaccine, developed by Xenova which was taken over by Celtic Pharma last year, works by binding cocaine, allowing it to be recognised by the immune system and limiting its ability to pass through the blood brain barrier to have its stimulant effect.

The Phase IIb study was carried out in 114 patients who had been taking cocaine for an average of 13 years, and were also receiving methadone to help wean them off heroin. The primary endpoint in the study was an improvement in abstinence from cocaine over a three-week period. TA-CD failed to improve this compared to placebo, manly because of an unexpectedly high placebo response.

“Nevertheless, some significant indications of efficacy were demonstrated in the study including twice as many patients in the treatment group achieving a 50% or greater increase in cocaine-free days as measured by urine analysis,” said Celtic Pharma in a statement.

A second, Phase IIa study in people not actively seeking to stop using cocaine reinforced that view, with ‘substantial’ reductions in reported cocaine use, according to the company.

The data were presented at a meeting of officials from the US National Institute on Drug Abuse, which sponsored the trials. Celtic Pharma said it would now discuss with the NIDA how to carry out further development of TA-CD, having earlier said it expected to start a Phase III programme for the product in late 2006.

The firm also said the findings of the studies would help direct the clinical programme for TA-NIC, its vaccine for nicotine addiction.

- Meanwhile, Celtic Pharma has made a $4 million payment to Neurobiological Technologies in connection with its purchase of worldwide rights to the latter’s Xerecept (synthetic corticorelin acetate) product, currently in Phase III testing for swelling in the brain caused by cancer. The two companies agreed a $33 million licensing deal for the drug last September.