Time course of loss of clinical benefit following withdrawal of levodopa/carbidopa and bromocriptine in early Parkinson's disease.

Putative neuroprotective agents for Parkinson's disease can be assessed in untreated patients using progression of clinical disability as an index of disease progression. To avoid the confound associated with symptomatic therapy, progression of the underlying disease can be assessed by evaluating the progression of clinical disability from an untreated baseline to a final visit following wash-out of symptomatic medication. In this type of analysis it is critical to use a wash-out of sufficient duration to ensure elimination of symptomatic effects.