Comtan is entacapone. This can be taken in addition to Sinemet (which is levodopa and carbidopa). So, your father is taking every three hours:
300mg levodopa
75mg carbidopa
200mg entacapone
It is the levodopa that does the job, the carbidopa and entacapone increase the availability of the levodopa.

The same effect can be found by taking Stalevo which contains all three (levodopa, carbidopa, entacapone) in one pill.

Wikipedia states [1]:
"The most frequent undesirable effects caused by entacapone relate to the increased effects of L-DOPA, such as involuntary movements (dyskinesias). These occur most frequently at the beginning of entacapone treatment."

The entacapone increases the effectiveness of the levodopa by about 33% [2]. So, in your father's case it's equivalent to increasing his levodopa from 300mg to 400mg every three hours. This is a significant difference, and must be considered a possible cause of the "speedy" feeling.

I would discuss the situation with your father's doctor.

I am not a doctor, but if I were in this situation, I would slowly reduce the levodopa, not the entacapone. This is because the levodopa acts more directly. In Stalevo, all pills across wide range of levodopa strengths come with 200mg entacapone [3].

There may be good reasons for it, but you father's daily intake of levodopa is high.

References

[1] http://en.wikipedia.org/wiki/Entacapone

[2] http://www.birmingham.ac.uk/Document...hLEDReview.pdf

[3] http://en.wikipedia.org/wiki/Stalevo

John