schwad01,

I agree with you: "diarrhea might affect absorption directly or transit time." I think that rather than the "PD significantly worsens", it is more likely that the drug regimen becomes less effective.

I have more experience of the opposite problem, constipation. This is certainly associated with the effectiveness of my levodopa based drugs. But, I'm not sure of the direction of causality.

Going back to diarrhea, there seems little advantage in taking a levodopa pill only to have it defecated away before being absorbed. It might be worth discussing with your doctor temporarily changing your drug regimen, taking into account the timing of the defecations relative to the doses and trying to estimate the dose that has been lost, increasing the daily dose accordingly.

It may also be worth considering a skin patch.

After a course of antibiotics I eat a lot of live yogurt.

John