Medication can be used to improve the main symptoms of Parkinson’s disease, such as tremors (uncontrollable shaking) and movement problems.
However, not all the medications available 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
Your specialist can explain your medication options, including the risks associated with each medication, and discuss which may be best for you. Regular reviews will be required as the condition progresses and your needs change.
Most people with Parkinson's disease will eventually need to have a medication called levodopa.
Levodopa is absorbed by the nerve cells in your brain and turned into the chemical dopamine, which is used to transmit messages between the parts of the brain and nerves that control movement. Increasing the levels of dopamine using levodopa usually improves movement problems.
Levodopa is usually taken as a tablet or liquid and is often combined with other medication, such as benserazide or carbidopa. These additional medications stop the levodopa being broken down in the bloodstream before it has a chance to get to the brain. They also reduce the side effects of levodopa, which include feeling sick (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, its effects can be less long-lasting over the following years because, as more nerve cells in the brain are lost, 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 also linked to problems such as uncontrollable, jerky muscle movements (dyskinesias) and 'on-off' effects – where the person suddenly switches between being able to move (on) and being immobile (off).
If you have severe on-off swings, a type of levodopa called duodopa may be used.
This medication comes as a gel that is continuously pumped into your gut through a tube inserted through your abdominal wall (tummy). There is a small external pump attached to the end of the tube, which you wear on your belt.
However, only a few centres in the UK offer this treatment. It needs the support of your local NHS clinical commissioning group (CCG) to finance it.
Dopamine agonists act as a substitute for dopamine in the brain and have a similar but milder effect compared to levodopa. They are used to treat early Parkinson’s disease as they are less likely to cause involuntary movements (dyskinesias) than levodopa.
Dopamine agonists are often taken as a tablet, but a type called apomorphine can be injected under the skin (subcutaneously). Sometimes, dopamine agonists are taken at the same time as levodopa as this allows lower doses of levodopa to be used.
Possible side effects of dopamine agonists include nausea, vomiting, tiredness and dizziness. Dopamine agonists can also cause hallucinations and episodes of confusion, 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 addictive gambling and an excessively increased libido.
Talk to your healthcare specialist if you think you may be experiencing these problems. As the person themselves may not realise the problem, it is key that carers and family members also note any abnormal behaviour and discuss it with an 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. 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 brain chemical that destroys dopamine (monoamine oxidase-B).
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.
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 tests to check your liver health every two weeks.
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