How long have you been able to stay on the same dose of Sinemet before it no longer works and you need to increase the amount?

As I said in another post, I've had Parkinson's for 11 years and have been symptom free for 10 1/2 of those 11 years. I take Mirapex and Artane which, combined, worked wonders for me. It finally caught up with me and I need to change medications.

I see a new neurologist next week and am pretty sure will be put on Sinemet.

While I know that everyone is different, I'd like to get an idea of what to expect so if you can answer the question in my first sentence I'd be appreciative.