Summary: The nature and extent of the variability associated with L-dopa absorption has been investigated in 49 fasting healthy volunteers. Blood level profiles of dopa were obtained on 66 occasions after the ingestion of 1 gm of a solid dosage form of the drug.

There were no significant differences in L-dopa absorption from three formulations used in the study. However, there were large differences in the ability of individuals to absorb the drug intact.

Peak plasma concentrations of dopa ranged from 0.25 to 2.42 μg/ml and occurred from 30 minutes to 4 hours after ingestion. In 40 percent of trials, there were two or more peaks of dopa concentration. Overall bioavailability, as indicated by the computed area under the plasma level curve, was also very variable. There appeared to be greater variability between individuals than between separate trials on the same individual.

The mechanism of L-dopa absorption and the likely contribution of gastric emptying to the observed variability are discussed.