Factors affecting levodopa effects in Parkinson's disease.

Levodopa is the gold standard for the treatment of Parkinson's disease (PD) because of its outstanding clinical efficacy. However, the majority of patients experience various adverse reactions, including the wearing-off phenomenon, the on-off phenomenon, dyskinesia and psychiatric symptoms. The response to levodopa depends not only on the intrinsic responsiveness of the patients, but also on various other important factors including the type of levodopa preparation, its absorption/metabolism, the blood-brain barrier, age at onset of disease and concomitant use of anti-parkinsonian drugs. This review summarizes factors which influence the effects of levodopa in PD. To minimize levodopa-induced adverse reactions and to relieve long-term parkinsonian symptoms, levodopa therapy should be conducted by taking these factors into consideration.