Episodic unresponsiveness to single doses of L-dopa in parkinsonian fluctuators.

Episodic total unresponsiveness to single doses of L-dopa developed in 14 of 32 parkinsonians with declining efficacy and response fluctuations after chronic L-dopa therapy. Complete lack of clinical benefit after occasional doses was unpredictable, occurred at least once daily mostly in the afternoon, and differed from other response failures related to food intake. In two patients, total unresponsiveness after dose ingestion coincided with lack of increases in plasma L-dopa levels suggesting that phenomenon was due, in part, to failure of L-dopa absorption from the gut.