OBJECTIVES: Several cases of syndrome of inappropriate antidiuresis induced by anti-Parkinson agents have been reported. Our previous study demonstrated that pergolide and pramipexole stimulated elevation of plasma arginine vasopressin (AVP) levels in some patients with Parkinson's disease (PD), but that levodopa/carbidopa (300/30 mg/day) did not affect plasma AVP levels in treatment-naïve PD patients. On the basis of the binding profile of ropinirole to monoamine receptors, we hypothesized that ropinirole does not stimulate AVP secretion. The aim of this study was to test this hypothesis.
METHODS: Inclusion criteria were patients with probable PD suffering from a wearing-off phenomenon and who had been treated using levodopa/carbidopa with or without entacapone, but not with other classes of anti-Parkinson agents. Patients were excluded if they had at least one condition that could be associated with high AVP levels. Ropinirole was initiated at 0.5 mg 3 times daily, and daily dosages were increased by 1.5 mg/day on a biweekly basis up to 6 mg/day. Plasma AVP levels were determined every two weeks. Effects of escalating ropinirole dosage on plasma AVP levels were evaluated using a one-way analysis of variance for repeated measures, an a priori Dunnett multiple comparison test, and a regression analysis.
RESULTS: Of 16 patients enrolled, 11 patients (four males and seven females) completed the study. There was no statistically significant dose-response relationship between the ropinirole dosage and plasma AVP levels.
CONCLUSION: A minimal therapeutic dosage of ropinirole did not affect plasma AVP levels in patients with PD taking levodopa.