I am just an ol' lay person, not a doctor, but this is what it says on a Sinemet CR package insert dated 2002:

Following initiation of therapy, doses and dosing intervals may be increased or decreased depending upon therapeutic response. Most patients have been adequately treated with doses of SINEMET CR that provide 400 to 1600 mg of levodopa per day, administered as divided doses at intervals ranging from 4 to 8 hours during the waking day. Higher doses of SINEMET CR (2400 mg or more of levodopa per day) and shorter intervals (less than 4 hours) have been used, but are not usually recommended.

Over time, levodopa loses efficacy and it become necessary to take more per day, often in smaller doses taken more frequently.

The following passages from the package insert are also of interest - to me, at least. They are interesting in view of the widely held theory that continuous administration of levodopa will eliminate dyskinesia and/or motor fluctuations:

With SINEMET CR there is less variation in plasma levodopa levels than with SINEMET* (Carbidopa-Levodopa), the conventional formulation. However, SINEMET CR (Carbidopa-Levodopa) Sustained-Release is less systemically bioavailable than SINEMET (Carbidopa-Levodopa) and may require increased daily doses to achieve the same level of symptomatic relief as provided by SINEMET (Carbidopa-Levodopa).

and

In clinical trials, patients with moderate to severe motor fluctuations who received SINEMET CR did not experience quantitatively significant reductions in ‘off’ time when compared to SINEMET (Carbidopa-Levodopa).

and

Patients receiving SINEMET CR may develop increased dyskinesias compared to SINEMET (Carbidopa-Levodopa).

In fact, the prevalence of dyskinesia in the clinical trial cited in the package insert is 35% higher with sinemet CR than with plain old sinemet.

Hope that helps.

boann