The biomarker advantage of pramipexole, however, did not translate into a clear, clinically meaningful advantage. Indeed, although patients

on pramipexole had a lower incidence of complications, patients randomized to initial levodopa had an early and sustained improvement in function, and less somnolence and edema. In the ELLDOPA trial15 during which three increasing doses Inhibitors,research,lifescience,medical of levodopa were compared with placebo in patients with early Parkinson’s disease not requiring dopaminergic therapy, discordant results were noted between the clinical outcomes and the neuroimaging end point. Analysis of the 123I-b-CIT Go 6983 mw outcome suggested a trend toward a. more rapid decline in striatal dopamine transporter in individuals on the highest doses of levodopa, Inhibitors,research,lifescience,medical but the largest, clinical improvement, was observed in the levodopa. group, in the direction opposite to what would be predicted on the basis of the imaging marker. These results corroborate those of the CALM-PD trial, and indicate that the SPECT 123I-b-CIT biomarker advantage did not translate into a clinically meaningful Inhibitors,research,lifescience,medical advantage. Studies using 18F6-fluoro-L-dopa (F-dopa) positron emission tomography (PET) as a surrogate outcome of Parkinson’s

disease treatment, show similar negative results. The accumulation of these radioactive dopamine metabolites within the striatum, and evidence Inhibitors,research,lifescience,medical correlating their reduction with clinical and pathologic measures,16-18 make F-dopa PET a potential surrogate outcome for treatment assessment. In the REAL PET trial, 2 years after starting treatment, a. 13% decline in F-dopa uptake was seen in the ropinirole group compared with a. 20% decline in the levodopa group.19 However, patients treated with levodopa had significantly greater functional improvement and fewer side effects (excepting dyskinesia), suggesting that F-dopa PET did not, meet criteria for a surrogate outcome of treatment, efficacy. Additional Inhibitors,research,lifescience,medical concerns regarding the

ability to utilize PET as a. marker of therapeutic efficacy come from studies evaluating the safety and efficacy of fetal tissue transplantation.20-22 In these studies, a significant, increase in F-dopa uptake was demonstrated in patients receiving fetal PAK6 tissue transplantation. Regrettably, functional improvement, was not, clearly established, and a significant proportion of treated subjects in both studies developed disabling dyskinesias. This is a. clear example of a case where unexpected consequences of an intervention, not detected by a potential surrogate outcome, resulted in patient harm. The negative results of these trials have raised questions regarding the use of biomarkers in Parkinson’s disease. How can drugs affect, a. biomarker that suggests a.