ROPINIROLE HYDROCHLORIDE

ROPINIROLE HYDROCHLORIDE — ropinirole hydrochloride tablet, coated
Physicians Total Care, Inc.

DESCRIPTION

Ropinirole hydrochloride is an orally administered non-ergoline dopamine agonist. It is the hydrochloride salt of 4-[2-(dipropylamino)ethyl]-1,3-dihydro-2H-indol-2-one monohydrochloride and has an empirical formula of C₁₆ H₂₄ N₂ O•HCl. The molecular weight is 296.84 (260.38 as the free base).

The structural formula is:

Ropinirole hydrochloride is a white to pale greenish-yellow powder with a melting range of 243° to 250°C and a solubility of 133 mg/mL in water.

Each round coated tablet contains ropinirole hydrochloride equivalent to ropinirole, 0.25 mg, 0.5 mg, 1 mg, 2 mg, 3 mg, 4 mg, or 5 mg. Inactive ingredients consist of: croscarmellose sodium, lactose monohydrate, magnesium stearate, microcrystalline cellulose, and one or more of the following: carmine, FD&C Blue No. 2 aluminum lake, hypromellose, iron oxides, POLYETHYLENE GLYCOLS, polysorbate 80, titanium dioxide.

CLINICAL PHARMACOLOGY

Mechanism of Action:

Ropinirole hydrochloride is a non-ergoline dopamine agonist with high relative in vitro specificity and full intrinsic activity at the D₂ and D₃ dopamine receptor subtypes, binding with higher affinity to D₃ than to D₂ or D₄ receptor subtypes.

Ropinirole has moderate in vitro affinity for opioid receptors. Ropinirole and its metabolites have negligible in vitro affinity for dopamine D₁ , 5-HT₁ , 5-HT₂ , benzodiazepine, GABA, muscarinic, alpha₁ -, alpha₂ -, and beta-adrenoreceptors.

Parkinson’s Disease:

The precise mechanism of action of ropinirole hydrochloride as a treatment for Parkinson’s disease is unknown, although it is believed to be due to stimulation of postsynaptic dopamine D₂ -type receptors within the caudate-putamen in the brain. This conclusion is supported by studies that show that ropinirole improves motor function in various animal models of Parkinson’s disease. In particular, ropinirole attenuates the motor deficits induced by lesioning the ascending nigrostriatal dopaminergic pathway with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in primates. The relevance of D₃ receptor binding in Parkinson’s disease is unknown.

Restless Legs Syndrome (RLS):

The precise mechanism of action of ropinirole hydrochloride as a treatment for Restless Legs Syndrome (also known as Ekbom Syndrome) is unknown. Although the pathophysiology of RLS is largely unknown, neuropharmacological evidence suggests primary dopaminergic system involvement. Positron emission tomographic (PET) studies suggest that a mild striatal presynaptic dopaminergic dysfunction may be involved in the pathogenesis of RLS.

Clinical Pharmacology Studies:

In healthy normotensive subjects, single oral doses of ropinirole hydrochloride in the range 0.01 to 2.5 mg had little or no effect on supine blood pressure and pulse rates. Upon standing, ropinirole hydrochloride caused decreases in systolic and diastolic blood pressure at doses above 0.25 mg. In some subjects, these changes were associated with the emergence of orthostatic symptoms, bradycardia, and, in one case, transient sinus arrest with syncope. With repeat dosing and slow titration up to 4 mg once daily in healthy volunteers, postural hypotension or hypotension-related adverse events were noted in 13% of subjects on ropinirole hydrochloride and none of the subjects on placebo.

The mechanism of postural hypotension induced by ropinirole hydrochloride is presumed to be due to a D₂ -mediated blunting of the noradrenergic response to standing and subsequent decrease in peripheral vascular resistance. Nausea is a common concomitant symptom of orthostatic signs and symptoms.

At oral doses as low as 0.2 mg, ropinirole hydrochloride suppressed serum prolactin concentrations in healthy male volunteers.

Ropinirole hydrochloride had no dose-related effect on ECG wave form and rhythm in young, healthy, male volunteers in the range of 0.01 to 2.5 mg.

Ropinirole hydrochloride had no dose- or exposure-related effect on mean QT intervals in healthy male and female volunteers titrated to doses up to 4 mg/day. The effect of ropinirole hydrochloride on QT intervals at higher exposures achieved either due to drug interactions or at doses used in Parkinson’s disease has not been systematically evaluated.

Pharmacokinetics:

Absorption, Distribution, Metabolism, and Elimination:

The pharmacokinetics of ropinirole are similar in Parkinson’s disease patients and patients with Restless Legs Syndrome. Ropinirole is rapidly absorbed after oral administration, reaching peak concentration in approximately 1 to 2 hours. In clinical studies, over 88% of a radiolabeled dose was recovered in urine and the absolute bioavailability was 55%, indicating a first-pass effect. Relative bioavailability from a tablet compared to an oral solution is 85%. Food does not affect the extent of absorption of ropinirole, although its T_max is increased by 2.5 hours and its C_max is decreased by approximately 25% when the drug is taken with a high-fat meal. The clearance of ropinirole after oral administration to patients is 47 L/hr (cv = 45%) and its elimination half-life is approximately 6 hours. Ropinirole is extensively metabolized by the liver to inactive metabolites and displays linear kinetics over the therapeutic dosing range of 1 to 8 mg 3 times daily. Steady-state concentrations are expected to be achieved within 2 days of dosing. Accumulation upon multiple dosing is predictive from single dosing.

Ropinirole is widely distributed throughout the body, with an apparent volume of distribution of 7.5 L/kg (cv = 32%). It is up to 40% bound to plasma proteins and has a blood-to-plasma ratio of 1:1.

The major metabolic pathways are N-despropylation and hydroxylation to form the inactive N-despropyl and hydroxy metabolites. In vitro studies indicate that the major cytochrome P₄₅₀ isozyme involved in the metabolism of ropinirole is CYP1A2, an enzyme known to be stimulated by smoking and omeprazole, and inhibited by, for example, fluvoxamine, mexiletine, and the older fluoroquinolones such as ciprofloxacin and norfloxacin. The N-despropyl metabolite is converted to carbamyl glucuronide, carboxylic acid, and N-despropyl hydroxy metabolites. The hydroxy metabolite of ropinirole is rapidly glucuronidated. Less than 10% of the administered dose is excreted as unchanged drug in urine. N-despropyl ropinirole is the predominant metabolite found in urine (40%), followed by the carboxylic acid metabolite (10%), and the glucuronide of the hydroxy metabolite (10%).

P₄₅₀ Interaction:

In vitro metabolism studies showed that CYP1A2 was the major enzyme responsible for the metabolism of ropinirole. Inhibitors or inducers of this enzyme have been shown to alter its clearance when coadministered with ropinirole. Therefore, if therapy with a drug known to be a potent inhibitor of CYP1A2 is stopped or started during treatment with ropinirole hydrochloride, adjustment of the dose of ropinirole hydrochloride may be required.

Population Subgroups:

Because therapy with ropinirole hydrochloride is initiated at a low dose and gradually titrated upward according to clinical tolerability to obtain the optimum therapeutic effect, adjustment of the initial dose based on gender, weight, or age is not necessary.

Age:

Oral clearance of ropinirole is reduced by 15% in patients above 65 years of age compared to younger patients. Dosage adjustment is not necessary in the elderly (above 65 years), as the dose of ropinirole is to be individually titrated to clinical response.

Gender:

Female and male patients showed similar oral clearance.

Race:

The influence of race on the pharmacokinetics of ropinirole has not been evaluated.

Cigarette Smoking:

Smoking is expected to increase the clearance of ropinirole since CYP1A2 is known to be induced by smoking. In a study in patients with RLS, smokers (n = 7) had an approximate 30% lower C_max and a 38% lower AUC than did nonsmokers (n = 11), when those parameters were normalized for dose.