Beginning-of-dose motor deterioration following the acute administration of levodopa and apomorphine in Parkinson's disease.

Six Parkinsonian patients on long term levodopa therapy complained of short-lived deterioration of Parkinsonian symptoms immediately after levodopa intake. After withdrawal of the drug overnight, and following an oral challenge with levodopa/carbidopa (250/25) in all six cases, and with subcutaneous apomorphine (3 mg) in two, deterioration below base line levels of disability were observed which would not be explained by loss of sleep benefit. This occurred 10-20 minutes after levodopa challenge and lasted for 10-20 minutes. The latency and duration of this phenomenon were shorter with apomorphine but the characteristics were similar. This phenomenon may be due to an inhibitory effect of levodopa acting via presynaptic dopamine receptors.