The aim of this study was to examine the effects of the peripheral dopamine D2-receptor antagonist, domperidone, on the plasma kinetics of levodopa in patients with Parkinson disease (PD).
In a randomized crossover design, 18 hospitalized patients with PD received a single dose of levodopa/benserazide, 100/25 mg, with or without domperidone, 10 mg, under fasting conditions. Plasma levodopa concentrations were determined up to 3 hours after dose administration.
Mean ± SEM levodopa maximum plasma concentration (Cmax) (14.1 ± 2.9 vs 9.7 ± 1.6 μmol/L; P < 0.01), plasma concentration at 30 min (C30 min) (13.7 ± 3.0 vs 8.1 ± 2.0 μmol/L; P < 0.01), and area under the plasma concentration-time curve from 0 to 3 hours (AUC0–3 hr) (15.9 ± 3.1 vs 12.1 ± 2.4 μmol/L · hour; P < 0.05) were significantly higher after coadministration of levodopa with domperidone compared to levodopa alone. Thus, domperidone increased levodopa Cmax and AUC0–3 hr by 1.5- and 1.3-fold, respectively. There were no exacerbations of PD by concomitant domperidone administration.
The results demonstrate that coadministration of domperidone increased the bioavailability of levodopa. This may be the reason for no exacerbation of PD in concomitant administration of domperidone, a dopamine D2-receptor blocker.