By co-incidence, Prof. Frank Church has recently written an interesting post about B vitamins (folate, B6, B12) and carbidopa/levodopa therapy.
The main message seems to be that, if you take c/l, don't overdo the vitamin B6 supplements.
B Vitamins (Folate, B6, B12) Reduce Homocysteine Levels Produced by Carbidopa/Levodopa Therapy | Journey with Parkinson's