Introduction: Previous studies have suggested a significant increase in plasma homocysteine (Hcy) levels in levodopa-treated Parkinson's disease (PD) patients, and vitamin B12 and folate supplementation may decrease Hcy levels. However, the effects of catechol-O-methyltransferase inhibitors on levodopa-induced increase in Hcy levels were conflicting. The aim of this study was to evaluate whether Hcy levels are increased in levodopa-treated PD patients and to evaluate the effects of vitamin B12 and folate or entacapone on Hcy levels in levodopa-treated PD patients.

Methods: We analyzed and compared plasma Hcy levels in 20 levodopa-naïve PD patients and 42 levodopa-treated PD patients, followed by randomized assignment of 42 levodopa-treated patients to treatment groups with either vitamin B12 and folate, entacapone, or no medication.

Results: Plasma Hcy levels in levodopa-treated PD patients were higher than those in the control group, but the difference was not statistical significant (15.25 ± 6.70 and 13.13 ± 4.68, P = 0.216). Patients treated with vitamin B12 and folate had a significant decrease in plasma Hcy levels (P < 0.001). In the entacapone group, Hcy levels were mildly decreased, but the change did not reach statistical significance.

Conclusion: Levodopa-treated PD patients had higher plasma Hcy than levodopa-naive PD patients. Unlike entacapone, combination supplementation with vitamin B12 and folate was associated with significantly decreased plasma Hcy. We suggest that plasma Hcy levels should be monitored during levodopa treatment, and supplementation with inexpensive vitamin B12 and folate is beneficial for levodopa-treated patients.