The base-line treatment of Parkinsonism is levodopa + carbidopa combination. Ropinirol can be used either alone or more commonly as an adjunct with base-line therapy i.e. levodopa + carbidopa + ropinirol. There are no unacceptable interactions in these three drugs. Generally the addition of ropinirol results in the dose reduction of levodopa combination by about 20 per cent.
Just like ropinirol, entacapone is also used as an adjunct to the base-line treatment. Entacapone increases the blood levels of levodopa combinations and hence is useful. However it may aggravate levodopa-induced hypotension (low BP).
In other words, one can use levodopa + carbidopa + ropinirol or levodopa + carbidopa + entacapone. The adverse reactions of ropinirol and entacapone are similar and additive; they are not recommended to be used together.