Plasma levodopa peak delay and impaired gastric emptying in Parkinson's disease

Objectives: Whereas delayed gastric emptying is believed to be a causative factor for producing delayed-on and motor fluctuation in Parkinson's disease (PD), few studies have directly measured levodopa pharmacodynamics and gastric emptying together. In order to determine the relationship, we measured these two parameters in a single PD patients cohort. Methods: Thirty-one patients with PD were enrolled in the study. They were 11 men and 20 women; age, 68.1 +/- 7.8 years; disease duration, 4.2 +/- 3.8 years; Unified Parkinson's Disease Rating Scale Part 3. Motor Score 18.37 +/- 8.60; bowel movement <3 times a week in 20; all taking 301 mg +/- 94 mg/day levodopa/carbidopa. All patients underwent levodopa pharmacokinetic study and the gastric emptying study using C-13-octanoic acid expiration breath test Statistical analysis was performed by Student's t-test and Mann-Whitney's U test. Results: Pharmacokinetic study showed that the plasma levodopa peak was at 2 hours in 42% (13/31 patients) whereas at 1 hour in 58% (18/31 patients), total of 50.7 +/- 16.4 min (mean +/- standard deviation) in all 31 patients. The gastric emptying study showed that T-max (C-13) > 60 min was more common in patients with a plasma levodopa peak at 2 hours (14/18, 69%) than in those with a plasma levodopa peak at 1 hour (4/13, 22%) (p < 0.05), total of 50.7 16.4 min in all 31 patients. Conclusion: We found a significant relationship between levodopa pharmacokinetics and gastric emptying in PD patients, suggesting that delayed gastric emptying is a causative factor for producing delayed-on in PD. Therefore, studies of improved gastric emptying in order to ameliorate delayed-on in PD are warranted. (C) 2012 Elsevier B.V. All rights reserved.