P. 505-509Levodopa combined with carbidopa constitutes one of the most frequent medication in the treatment of Parkinson’s disease. Plantago
ovata husk (water-soluble fiber) improves levodopa absorption conditions, but when this drug is administered with carbidopa, fiber could
reduce its effectiveness. The purpose of this study is to investigate whether the presence of P. ovata husk modifies in rabbits the
bioavailability and other pharmacokinetic parameters of levodopa (20 mg/kg) when administered by the oral route with carbidopa (5 mg/
kg). We have also studied whether pharmacokinetic modifications are fiber–dose dependent (100 and 400 mg/kg). When levodopa and
carbidopa were administered with 100 mg/kg P. ovata husk, the value of AUC for levodopa diminishes 29.7% (sign, n =6, P b0.05) and
Cmax 28.1% (sign, n =6, P b0.05) in relation to the values obtained when these drugs were administered without fiber. If the dose of fiber
was 400 mg/kg, the decrease was smaller: 20.4% for AUC (no significant difference) and 24.6% for Cmax (sign, n =6, P b0.05), that may
indicate an inhibitory action of AADC by the fiber or any of its partial hydrolysis products. On the other hand, since certain time on,
levodopa concentrations are always higher in the groups that receive fiber: 210 min with 100 mg/kg and 150 min with 400 mg/kg. The
administration of P. ovata husk with levodopa/carbidopa to patients with Parkinson disease could be beneficial and in particular in those
patients who also suffer constipation due to an improvement of levodopa kinetic profile with higher final concentrations, a longer plasma
half-life and lower Cmax.S
