NDARC Technical Report No. 140 (2002)
Cocaine dependence is a serious personal and public health issue in some developed countries and is becoming one in some developing countries. It is difficult to treat because of the modest effectiveness of existing psychosocial and pharmacological treatments.
A cocaine vaccine acts on cocaine molecules in the bloodstream to substantially reduce the amount of cocaine that crosses the blood-brain barrier to act on receptors in the brain. It involves administering a complex molecule of cocaine and immunogenic proteins which induces the formation of antibodies that bind to cocaine and its psychoactive metabolites. These molecular complexes are too large to cross the blood-brain barrier and so prevent cocaine from reaching the brain.
There are two other types of Peripheral Cocaine Blocking Agent (PCBA) that act in similar ways to a cocaine vaccine. A second type of PCBA increases the amount or the level of activity of naturally occurring enzymes that metabolise cocaine in the blood and liver. Any cocaine that is administered while these enzymes are present in the blood is metabolised before it reaches the brain. The third type of PCBA involves using a cocaine-protein complex to induce an antibody to cocaine that accelerates the metabolism of cocaine in plasma, thereby reducing the amount of cocaine that crosses the blood-brain barrier.
A cocaine vaccine and the other PCBAs have a number of potential advantages over existing drug treatments, namely, they block cocaine from entering the brain, they may have fewer side effects, and they are likely to have better rates of patient compliance because they are administered less often than oral drugs.
The evidence of their effectiveness is confined to studies using animal models of cocaine dependence. These results, and the results of one phase 1 clinical trial, are sufficiently promising to warrant human trials of efficacy. Human clinical trials of the efficacy and safety of a cocaine vaccine will need to address the standard ethical issues of informed consent and rigorous trial design.
If a cocaine vaccine proves effective in human clinical trials, the least ethically problematic use will be using cocaine antibodies or cocaine-metabolising enzymes to manage cocaine toxicity and overdose.
A cocaine vaccine will not be a stand alone treatment for cocaine dependence. When used in the context of good psychosocial care it may improve abstinence rates but it is unlikely to completely block the effects of smoked or injected cocaine. Patients will be able to over-ride its effects by increasing their dose of cocaine or by using other stimulant drugs. The effectiveness of a vaccine may be improved by using it in combination with other PCBAs and with other pharmacotherapies for cocaine dependence.
The use of a cocaine vaccine to treat cocaine dependent persons will be ethically acceptable when used in voluntary patients who have given free and informed consent to their use. In this setting, an abstinent cocaine dependent patient may either be “passive immunised” with cocaine antibodies or actively immunised against cocaine in order to reduce their risk of relapsing to cocaine use. The major ethical issues with this use of a vaccine or antibodies is in ensuring that patients give free and informed consent to treatment.
One possible ethical issue with a cocaine vaccine will be in protecting patient privacy and preventing discrimination against recove ring addicts on the basis of cocaine antibody in their blood. This problem is not wholly new: similar issues have been addressed in methadone maintenance treatment for heroin dependence and with HIV seropositivity in injecting drug users. Similar legislative and public education approaches may minimise these problems with a vaccine. The severity of the problem may also be reduced by using “passive” immunisation with monoclonal cocaine antibodies that disappear from the body after some weeks.
The use of a cocaine vaccine to treat legally coerced clients poses more ethical problems. It is arguably ethical to use it in this way if and only if offenders are offered constrained choices of (a) whether or not to accept treatment and (b) the type of treatment that they accept. Any coerced use of a cocaine vaccine should be done cautiously and only after considerable clinical experience with its use with voluntary patients. Any use in patients under legal coercion should be on a trial basis with rigorous evaluation of its safety, effectiveness and cost-effectiveness. The evaluation would also need to examine any adverse health, social or ethical consequences that it may have before it was more widely implemented.
The preventive use of a cocaine vaccine is even more ethically contentious. Any trials of its preventive use should be preceded by extensive clinical experience with a cocaine vaccine in voluntary patients who are cocaine dependent. A higher standard of safety will also need to be met if a vaccine is to be used preventively. Important ethical issues are also raised by such a use, namely, the capacity of minors to consent to its use, the rights of parents to make decisions about vaccination on behalf or their children, the protection of privacy, and the prevention of discrimination against children who have been vaccinated.
Citation: Hall, W. and Carter, L. (2002) Ethical issues in trialling and using a cocaine vaccine to treat and prevent cocaine dependence, Sydney: National Drug and Alcohol Research Centre.