Apomorphine in Parkinson's disease
Apomorphine is a dopamine agonist — a drug which stimulates dopamine receptors and produces a direct effect at the sites where dopamine is active in the brain.
Most people with Parkinson's disease (PD) who are treated with levodopa find that their medication becomes less effective over a period of time. Some experience sudden fluctuations in their symptoms in spite of all efforts to adjust their medication. The incidence of these disabling 'on-off' fluctuations increases with the duration of treatment, and many people may be affected by years of sustained therapy.
An 'on' period describes the time when benefit is achieved from the medication and disability is at a minimum. An 'off' period describes the time when benefit from medication is less obvious or not achieved at all. People may become virtually immobile and 'freeze', becoming unable to walk during an 'off' period. In these situations, injections of apomorphine may be tried in addition to the usual tablets. Apomorphine rapidly and consistently reverses the 'off' period.
Methods of administration
Apomorphine may be injected into various areas of the body: the anterior abdominal wall, a thigh, or upper arm. It is given by subcutaneous (under the skin) injection.
This means that it starts to work much more quickly than tablets or capsules, and is usually active within 5 to 10 minutes with the benefits lasting for about an hour. This rapid effect has resulted in apomorphine being called a 'rescue' drug, as it can restore mobility or prevent a period of disability from occurring.
The drug may be given either intermittently or by continuous infusion administered using a pump syringe driver. Researchers overseas are developing a nasal spray which may make it much easier to use.
People with PD are usually taught to administer the drug themselves or, if this is difficult, a carer or nurse can provide assistance. The timing is important, as people who are self-administering and wait until the 'off' period is well established may find that the tremor and rigidity may prevent them from being able to inject.
A filled syringe can be kept in the fridge for up to 24 hours; if not used after 24 hours it is discarded.
To counteract nausea, people are routinely treated with domperidone (a peripheral dopamine receptor agonist) before starting apomorphine therapy. The domperidone is gradually reduced over the first 3 to 6 months of treatment and is discontinued where possible.
Advantages
Apomorphine acts very quickly and reliably so that people who need to be active at specific times can continue with their normal activities. It can bring great relief to people with extreme variations in mobility or severe involuntary movements.
Disadvantages
Apomorphine helps only those people who are still responding to medications such as Sinemet or Madopar. It causes nausea and therefore another drug, domperidone (which acts specifically against nausea and sickness) has to be taken as well, at least in the first few months of apomorphine use. As apomorphine can only be given by injection, patients and/or carers have to be able to cope with this and training is usually required. Soreness and skin reactions can develop at the injection sites. Other side effects that can sometimes occur include drowsiness, confusion and hallucinations.
Research
Apomorphine is being used in Victoria as a tool in a research project. Brain circuitry is being studied using positron-emission tomography studies to see which parts of the brain change their levels of activity as a person goes from the 'off' to 'on' stages.
Last Reviewed: 19 July 2002
