lurkingforacure writes:

"We are at the point to where we can't really tell if we've taken pills or not-we feel crappy most of the time. This has been going on before our Mylan generic got switched over to Sun, though. The neuro agrees we're undermedicated, and that the therapeutic dose probably needs to increase, but doesn't want to increase because that would put us at 1,000mg/day. Or more. Yikes."

A number of issues are raised here.

1. The maximum dose of levodopa.
See the thread "Max Sinemet Dosage????", ashleyk, June 2015
Max Sinemet Dosage???
For the reasons explained there, I see no reason for an arbitrary limit of 1000mg/day of levodopa: for some PwP it will be too much, while for others they could benefit from more.

2. The maximum dose of carbidopa.
Brod et al. write[1]:
"Recommended doses of carbidopa are 75–200 mg/day. Higher doses could inhibit brain aromatic amino acid decarboxylase and reduce clinical effects."
However, their work shows:
"Doses of 450 mg/day of carbidopa did not reduce the responses to levodopa infusion, extending the safe range of carbidopa to 450 mg/day."
So, with a normal ratio of 4:1 levodopa:carbidopa this would indicate a maximum of 1800mg/day of levodopa. An alternative option is to take some of the levodopa dose in the 10:1 formulation.

3. The efficacy of generics.
Generics must satisfy bioequivalence rules. These are based on the pharmacokinetic parameters CMAX (maximum concentration) and AUC (area under the curve) [2]:
"The FDA considers two products bioequivalent if the 90% CI of the relative mean Cmax, AUC(0–t) and AUC(0–∞) of the test (e.g. generic formulation) to reference (e.g. innovator brand formulation) should be within 80% to 125% in the fasting state."
This is complicated. It is couched in probabalistic terms. I make a very rough estimate that this means that it is OK, as far as the regulators are concerned, for variations of up to 5% by weight of the active component to be acceptable. This variation is noticeable by PwP. They would notice that they went "off" sooner than usual or that they never crossed the "on" threshold.

References

[1] "Are high doses of carbidopa a concern? A randomized clinical trial in Parkinson’s disease"
Lissa S. Brod, MD,1,2 Jason L. Aldred, MD,1,2 and John G. Nutt, MD1,
Mov Disord, Apr 2012
Are high doses of carbidopa a concern? A randomized clinical trial in Parkinson’s disease

[2] Bioequivalence - Wikipedia

John