Treatment of Parkinson’s disease

Mr. Lacy is a 65-year-old man diagnosed with Parkinson’s disease (PD) five years ago. His disease has progressed over the years, and it is recommended that he be treated with levodopa.
Q3. What is levodopa, and how is it used in the treatment of Parkinson’s disease? What are the adverse effects of levodopa that might be expected in this patient?
Q4. What drug is most commonly combined with levodopa and why?
Q5. What other drugs can be used for the treatment of PD?