An open cross-over study of 20 patients with Parkinson's disease performed with 
two drugs containing L-dopa and a peripheral aromatic amino acid decarboxylase 
inhibitor (benserazide, carbidopa) confirmed the conclusions reached in other 
clinical trials that this combined treatment of Parkinson's disease is the most 
effective form of drug therapy available at present. With both drugs, Madopar or 
Sinemet, an optimum therapeutic result was obtained with relatively small doses 
of L-dopa (the reduction in L-dopa dosage amounting to about 80%). A loss of 
efficacy with both drugs, which has observed during long-term treatment of 
patients with Parkinson's disease, could be avoided by switching the patients 
from Sinemet to Madopar and vice versa. Determination of L-dopa in the plasma 
demonstrated that with either drug similar plasma levels of L-dopa were achieved 
during clinically effective treatment.