Requip PD Mechanism of Action

ATC Code: N04BC04.
Pharmacology: Pharmacodynamics: Mechanism of Action: Parkinson's disease is characterised by a marked dopamine deficiency in the nigral striatal system. Ropinirole is a non-ergoline D2/D3 dopamine agonist that alleviates this deficiency by stimulating striatal dopamine receptors.
Ropinirole acts in the hypothalamus and pituitary to inhibit the secretion of prolactin.
Clinical efficacy: A 36-week, double-blind, three-period crossover study, in monotherapy with a primary end point of change from period baseline in Unified Parkinson's Disease Rating Scale (UPDRS) total motor score was conducted in 161 patients with early phase Parkinson's disease. A subgroup analysis of patients initiated on monotherapy treatment with ropinirole immediate release tablets and switched overnight to the nearest equivalent dose of ropinirole prolonged-release tablets was consistent with similar efficacy from equivalent mg for mg doses. The adjusted mean difference between ropinirole prolonged-release tablets and Requip film-coated (immediate-release) tablets at study-endpoint was 0.7 points (95% CI: [-1.51, 0.10], p=0.0842).
Following the overnight switch to a similar dose of the alternative tablet formulation, there was no difference in the adverse event profile and less than 3% of patients required a dose adjustment (all dose adjustments were increases by one dose level. No patients required a dose increase).
A 24-week, double-blind, placebo-controlled, parallel group study in patients with Parkinson's disease who were not optimally controlled on levodopa demonstrated that adjunctive therapy of ropinirole prolonged-release tablets results in clinically relevant and statistically significant superiority over placebo in a change from baseline in awake time "off" (adjusted mean treatment difference -1.7 hours (95% CI: [-2.34, -1.09], p<0.0001). This was supported by secondary efficacy parameters of change from baseline in total awake time "on" (+1.7 hours (95% CI [1.06, 2.33], p<0.0001) and total awake time "on" without troublesome dyskinesias (+1.5 hours (95% CI: [0.85, 2.13], p<0.0001). Importantly, there was no indication of an increase from baseline in awake time "on" with troublesome dyskinesias, either from diary card data or from the UPDRS items.
Study of the effect of ropinirole on cardiac repolarisation: A thorough QT study conducted in male and female healthy volunteers who received doses of 0.5, 1, 2 and 4 mg of ropinirole film-coated (immediate release) tablets once daily showed a maximum increase of the QT interval duration at the 1 mg dose of 3.46 milliseconds (point estimate) as compared to placebo. The upper bound of the one sided 95% confidence interval for the largest mean effect was less than 7.5 milliseconds. The effect of ropinirole at higher doses has not been systematically evaluated.
The available clinical data from a thorough QT study do not indicate a risk of QT prolongation at doses of ropinirole up to 4 mg/day. A risk of QT prolongation cannot be excluded as a thorough QT study at doses up to 24 mg/day has not been conducted.
Pharmacokinetics: Absorption: Bioavailability of ropinirole is approximately 50% (36 to 57%). Following oral administration of ropinirole PR, plasma concentrations increase slowly, with a median time to C_max of between 6 and 10 hours.
In a steady-state study in Parkinson's disease patients receiving 12 mg of ropinirole PR once daily, a high fat meal increased the systemic exposure to ropinirole as shown by an average 20% increase in AUC (90% CI [1.12, 1.28]) and an average 44% increase in C_max (90% CI [1.34, 1.56]). T_max was delayed by 3.0 hours. However, in the studies that established the safety and efficacy of ropinirole PR, patients were instructed to take study medication without regard to food intake.
The system exposure to ropinirole is comparable for ropinirole prolonged-release tablets and ropinirole film-coated (immediate-release) tablets based on the same daily dose.
Distribution: Plasma protein binding of the drug is low (10 to 40%). Consistent with its high lipophilicity, ropinirole exhibits a large volume of distribution (approx. 7 L/kg).
Biotransformation: Ropinirole is primarily cleared by CYP1A2 metabolism and its metabolites are mainly excreted in the urine. The major metabolite is at least 100 times less potent than ropinirole in animal models of dopaminergic function.
Elimination: Ropinirole is cleared from the systemic circulation with an average elimination half-life of about 6 hours. The increase in systemic exposure (C_max and AUC) to ropinirole is approximately proportional over the therapeutic dose range. No change in the oral clearance of ropinirole is observed following single and repeated oral administration. Wide inter-individual variability in the pharmacokinetic parameters has been observed. Following steady-state administration of ropinirole prolonged-release tablets, the inter-individual variability of C_max was between 30% and 55% and for AUC was between 40% and 70%.
Special Patient Populations: Renal Impairment: There was no change observed in the pharmacokinetics of ropinirole in Parkinson's disease patients with mild to moderate renal impairment.
In patients with end stage renal disease receiving regular dialysis, oral clearance of ropinirole is reduced by approximately 30%. Oral clearance of the metabolites SKF-104557 and SKF-89124 were also reduced by approximately 80% and 60%, respectively. Therefore, the recommended maximum dose is limited to 18 mg/day in these patients with Parkinson's disease.
Toxicology: Preclinical safety data: Reproductive toxicity: In fertility studies in female rats, effects were seen on implantation due to the prolactin-lowering effect of ropinirole. It should be noted that prolactin is not essential for implantation in humans.
Administration of ropinirole to pregnant rats at maternally toxic doses resulted in decreased foetal body weight at 60 mg/kg/day (approximately twice the highest AUC at the maximum recommended human dose [MRHD]), increased foetal death at 90 mg/kg/day (mean AUC in rats is approximately 3 times the highest AUC at the MRHD) and digit malformations at 150 mg/kg/day (approximately 5 times the highest AUC at the MRHD). There were no teratogenic effects in the rat at 120 mg/kg/day (approximately 4 times the highest AUC at the MRHD) and no indication of an effect during organogenesis in the rabbit when given alone at 20 mg/kg (9.5 times the mean human C_max at the MRHD). However, ropinirole at 10 mg/kg (4.8 times the mean human C_max at the MRHD) administered to rabbits in combination with oral L-dopa produced a higher incidence and severity of digit malformations than L-dopa alone.
Toxicology: The toxicology profile is principally determined by the pharmacological activity of ropinirole behavioural changes, hypoprolactinaemia, decrease in blood pressure and heart rate, ptosis and salivation. In the albino rat only, retinal degeneration was observed in a long term study at the highest dose (50 mg/kg/day), and was probably associated with an increased exposure to light.
Genotoxicity: Genotoxicity was not observed in a battery of in vitro and in vivo tests.
Carcinogenicity: From two-year studies conducted in the mouse and rat at dosages up to 50 mg/kg there was no evidence of any carcinogenic effect in the mouse. In the rat, the only drug-related lesions were Leydig cell hyperplasia and testicular adenoma resulting from the hypoprolactinaemic effect of ropinirole. These lesions are considered to be a species specific phenomenon and do not constitute a hazard with regard to the clinical use of ropinirole.
Safety pharmacology: In vitro studies have shown that ropinirole inhibits hERG-mediated currents. The IC₅₀ is 5-fold higher than the expected maximum plasma concentration in patients treated at the highest recommended dose (24 mg/day), see Pharmacodynamics as previously mentioned.