Levodopa can cause-

Ans. is 'd' i.e., On-off phenomenon On-off phenomenon in Parkinsonism In parkinsonism the motor symptoms remain stabilized 2-3 years after therapy. o But after 2-3 years of levodopa therapy the effect of the drug gradually begins to wear offi.e., the motor symptoms begins to appear. This is also called "end of dose" deterioration. o After some period of time, the motor symptoms begins to appear frequently. This is called 'switches' or 'on-off effect. o With time "all or none" response develops i.e., the patient is alternately well and disabled. o This "on-off' phenomenon is probably a reflection of the progression of the disorder. With progressive degeneration of dopamine neurones, the ability of the drug to regulate the storage and release of Dopamine may be lost. Dopamine is then synthesized in the striatum on a moment to moment basis. This results in appearance of symptoms.