Medicines may be used to treat the symptoms of Parkinson’s disease. Not all medicines are useful for everyone, and the short and long-term effects of each are different. Three main types of medication are commonly used. These are levodopa, dopamine agonists and monoamine oxidase-B inhibitors. Most people with Parkinson's disease will eventually need to have levodopa, which may be taken at the same time as other medicines to boost its effects.
Each medicine is prescribed to suit the individual needs of the person taking it. Factors that can influence which medicine is prescribed include:
- your age
- the severity of your symptoms
- how well you respond to treatment
- whether you experience any side effects
When people do not take their medication on time, or stop taking it completely, they can become very ill. If you have to go into hospital, tell the hospital staff about your medication. If you have a stomach bug or are vomiting, tell your GP as this may affect the levels of medicine in your body.
Your specialist can explain your medication options and discuss which may be best for you. Regular reviews will be required as the disease progresses and your needs change.
Levodopa is absorbed by the nerve cells in your brain and turned into dopamine. It is usually taken as a tablet or liquid. Levodopa is often combined with other medication, such as benserazide or carbidopa. These drugs stop the levodopa being broken down in the gut before it has a chance to get to the brain. They also reduce the side effects of levodopa, which include nausea, vomiting, tiredness and dizziness.
If you are prescribed levodopa, the initial dose will usually be very small and will be gradually increased until it takes effect. At first, levodopa can cause a dramatic improvement in the symptoms. However, it usually becomes less effective over time. This happens because as more nerve cells in the brain die, there are fewer of them to absorb the medicine. This means that the dose may need to be increased from time to time.
Long-term use of levodopa is linked to certain side effects. These include "on-off" effects, where you can suddenly switch between being able to move (on) and being immobile (off), and muscle problems that cause uncontrollable, jerky muscle movements (dyskinesias).
This is a specialist treatment used for patients with severe on-off swings. A tube is inserted through the abdominal wall into the gut. Levodopa gel is continuously fed through the tube by a mini-pump, which is worn on your belt. Only a few centres in the UK offer this treatment, which needs the support of your primary care trust to finance it.
Dopamine agonists act as a substitute for dopamine in the brain and have a similar effect to levodopa. They are used to treat early Parkinson’s disease as they are less likely to cause muscle problems (dyskinesias) than levodopa. They are often taken as a tablet, but can also be injected into a vein (intravenously). Sometimes, dopamine agonists are taken at the same time as levodopa. This allows lower doses of levodopa to be used.
Possible side effects of dopamine agonists include nausea, vomiting, tiredness and dizziness. Dopamine agonists can cause episodes of confusion or hallucinations, so they need to be used with caution, particularly in elderly patients who are more susceptible.
For some people, dopamine agonists, especially at high doses, have been linked to the development of compulsive behaviours, including pathological gambling, increased libido and hypersexuality. These are very complex disorders. Talk to your healthcare specialist if you think you may be experiencing them. As the person themselves may not realise the problem, it is key that carers and family members note any abnormal behaviour and discuss it with the appropriate professional at the earliest opportunity.
If you are prescribed a course of dopamine agonists, the initial dose will usually be very small to prevent nausea. The dosage is gradually increased over a few weeks. If nausea becomes a problem, your GP may prescribe anti-sickness medication, such as domperidone. You may need blood tests and a chest X-ray before some types of dopamine agonist are prescribed.
Monoamine oxidase-B inhibitors
Monoamine oxidase-B (MAO-B) inhibitors, including selegiline and rasagiline, are another alternative to levodopa for treating early Parkinson's disease. They block the effects of a chemical called monoamine oxidase-B in the brain. This chemical destroys dopamine. By blocking it, MAO-B inhibitors allow dopamine to last longer in the brain.
Both selegiline and rasagiline can improve the symptoms of Parkinson’s disease, although their effects are small compared with levodopa. They can be used alongside levodopa or dopamine agonists.
MAO-B inhibitors can cause a wide range of side effects, including nausea, headache and abdominal pain, though not everyone will experience them.
Catechol-O-methyltransferase (COMT) inhibitors are prescribed for people in later stages of Parkinson’s disease. They prevent levodopa from being broken down by the enzyme COMT.
Side effects of COMT inhibitors include nausea, vomiting, diarrhoea and abdominal pain. If the COMT inhibitor tolcapone is used, you will need liver tests every two weeks.
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