RATE OF MOTOR RESPONSE TO ORAL LEVODOPA AND THE CLINICAL PROGRESSION OF PARKINSONS-DISEASE

We investigated the relationship between the rate of motor response af ter a standard levodopa oral dose and drug dynamic variables and disea se-related factors in 66 patients with Parkinson's disease. Time to ma ximum finger tapping effect was positively correlated with matched dur ation of levodopa dose response and fell from a median 120 minutes in patients at Hoehn and Yahr stage I and II to 60 minutes in stage IV pa tients (p < 0.001). The accelerated response to levodopa dose with the advancement of disease was also apparent as an increased steepness of the tapping effect versus time curve, with a shift from a hyperbolic to a sigmoid profile. The rate of motor response to oral levodopa may reflect the rate of dopamine interaction with the postsynaptic recepto rs, providing an indirect objective index of presynaptic dopaminergic homeostasis.