COMT inhibitors - Parkinson's drugs
COMT inhibitors are used to treat the symptoms of Parkinson's.
COMT inhibitors do not help Parkinson's on their own – they have to be used
COMT inhibitors reduce Parkinson's symptoms by blocking an
enzyme that breaks down levodopa, prolonging its effect.
There are branded and unbranded COMT inhibitors available. These
- entacapone (Comtess)
- tolcapone (Tasmar)
Entacapone (Comtess) can be taken with levodopa or
It is effective from the first dose and you should feel the
benefit within a day or two.
Comtess Medicine Guide for independent, up to date information
about this medicine.
Tolcapone was withdrawn from the UK in 1998 due to its effect on
liver function. However, in 2005, prescribing procedures were
heavily modified and tolcapone was reintroduced.
To avoid any potential risks, only physicians experienced in the
management of advanced Parkinson's will
be able to prescribe tolcapone. Patients must also undergo regular
Tolcapone Medicine Guide for independent, up to date
information about this medicine.
Advantages of COMT inhibitors
Be aware that other drugs (for Parkinson's or other conditions) can affect the action of COMT inhibitors.
The combination of apomorphine and entacapone needs careful supervision.
When used with levodopa, COMT
inhibitors can reduce the daily 'off' time and increase the 'on'
time. In many cases, the dose and frequency that levodopa is taken
can also be reduced.
The terms 'on/off' or 'motor fluctuations' refer to the period
when people can no longer rely on the smooth and even symptom
control that their drugs once gave them.
Read more in our Motor fluctuations in
Parkinson's information sheet.
Some disadvantages of COMT inhibitors
These drugs can increase the side effects caused by levodopa, notably dyskinesias (unwanted
involuntary movements), nausea and vomiting.
If these side effects increase after starting the drug, people
should raise the issue with their healthcare professional, as
reducing the levodopa dose can often help.
Be aware that other drugs (for Parkinson's or other conditions)
can affect the action of COMT inhibitors. The combination of
apomorphine and entacapone needs
Other reported side effects of COMT inhibitors include abdominal
pain, diarrhoea and discoloured urine.
Read more in our Drug treatments for
More drug treatments for Parkinson's
In this section
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