The effect of steady-state ropinirole on plasma concentrations of digoxin in patients with Parkinson's disease

Aims The aim of this single-blind study was to assess the effect of ropinir ole, a novel treatment for Parkinson's disease, on the steady-state pharmac okinetics and safety of digoxin in 10 patients with Parkinson's disease. Methods There were three parts to the study: digoxin once daily plus placeb o three times daily for 1 week; digoxin once daily plus ropinirole three ti mes daily for 6 weeks; and digoxin once daily plus placebo three times dail y for 1 week. Serial blood samples were collected over 24 h at the end of e ach part of the study for pharmacokinetic assessment. Pre-dose blood sample s were collected on specific days throughout the study to assess the attain ment of steady-state plasma levels of digoxin. The primary endpoints were A UC (0, tau) and C-max for digoxin. Results There was a mean decrease of 10% in digoxin AUC (0, tau) (90% CI: 0 .79, 1.01) and a 25% decrease in digoxin C-max (90% CI: 0.58, 0.97) when ro pinirole was co-administered, compared with digoxin alone. C-min plasma val ues for digoxin, however, were fairly constant throughout the study (point estimates 0.99, 95% CI: 0.85, 1.15). Changes in trough levels of digoxin ar e believed to be the most reliable way of assessing steady-state concentrat ions of digoxin, and therefore the clinical significance of an interaction. Changes in C-max are too readily influenced by other factors. Conclusions These results therefore indicate that on pharmacokinetic ground s no dose adjustment is necessary for digoxin co-administered with ropiniro le.