Clinical pharmacokinetics of ropinirole

Ropinirole is a selective non-ergoline dopamine D-2 receptor agonist indica ted for use in treating Parkinson's disease, When taken as oral tablets, ro pinirole is rapidly and almost completely absorbed, and it is extensively d istributed from the vascular compartment, The bioavailability is approximat ely 50%, Ropinirole shows low plasma protein binding, The drug is inactivat ed by metabolism in the liver, and none of the major circulating metabolite s have pharmacological activity, The principal metabolic enzyme is the cyto chrome P450 (CYP) isoenzyme CYP1A2. Ropinirole shows approximately linear pharmacokinetics when given as single or repeated doses, and is eliminated with a half-life of approximately 6 h ours. Population pharmacokinetics have demonstrated that gender, mild or mo derate renal impairment, Parkinson's disease stage and concomitant illnesse s or the use of several common concomitant medications have no effect on th e pharmacokinetics of ropinirole. Clearance is slower for patients older th an 65 years compared with those who are younger, and in women taking hormon e replacement therapy compared with those who are not. The CYP1A2 inhibitor ciprofloxacin produced increases in the plasma concentrations of ropinirol e when these 2 drugs were coadministered, but no interaction was seen with theophylline which, like ropinirole, is also a substrate for CYP1A2. There is no obvious plasma concentration-effect relationship for ropinirole.