Paliperidone (Page 7 of 10)

11 DESCRIPTION

Paliperidone extended-release tablets contain paliperidone,an atypical antipsychotic belonging to the chemical class of benzisoxazole derivatives. Paliperidone contains a racemic mixture of (+)- and (-)- paliperidone. The chemical name is (±)-3-[2-[4-(6-fluoro-1,2-benzisoxazol-3-yl)-1-piperidinyl]ethyl]-6,7,8,9-tetrahydro-9-hydroxy-2-methyl-4H-pyrido[1,2-a]pyrimidin-4-one. Its molecular formula is C23 H27 FN4 O3 and its molecular weight is 426.49. The structural formula is:

Chemical Structure
(click image for full-size original)

Paliperidone is sparingly soluble in 0.1N HCl and methylene chloride; practically insoluble in water, 0.1N NaOH, and hexane; and slightly soluble in N,N-dimethylformamide.

Paliperidone extended-release tablets are intended for oral administration and are available in 1.5 mg (brown), 3 mg (white), 6 mg (beige), and 9 mg (pink) strengths. Paliperidone extended-release tablets utilize OROS® osmotic drug-release technology.

Inactive ingredients are butylated hydroxytoluene, cellulose acetate, ferric oxide red, hydroxypropyl cellulose, hypromellose, polyethylene glycol, polyethylene oxides, povidone, stearic acid and sodium chloride. The film coating of 1.5 mg and 6 mg tablets contains ferric oxide red, ferric oxide yellow, ferrosoferric oxide, hypromellose, polyethylene glycol and titanium dioxide. The film coating of 3 mg tablets contains lactose monohydrate, hypromellose, titanium dioxide and triacetin. The film coating of 9 mg tablets contains ferric oxide red, hypromellose, polyethylene glycol and titanium dioxide.

The imprinting ink contains ammonium hydroxide, ferrosoferric oxide, isopropyl alcohol, N-butyl alcohol, shellac glaze and propylene glycol.

Delivery System Components and Performance

Paliperidone extended-release tablets use osmotic pressure to deliver paliperidone at a controlled rate. The delivery system, which resembles a capsule-shaped tablet in appearance, consists of an osmotically active trilayer core surrounded by a subcoat and semipermeable membrane. The trilayer core is composed of two drug layers containing the drug and excipients, and a push layer containing osmotically active components. There is one precision laser-drilled orifice on the drug-layer dome of the tablet. Each tablet strength has a different colored water-dispersible overcoat and print markings. In an aqueous environment, such as the gastrointestinal tract, the water-dispersible color overcoat erodes quickly. Water then enters the tablet through the semipermeable membrane that controls the rate at which water enters the tablet core, which, in turn, determines the rate of drug delivery. The hydrophilic polymers of the core hydrate and swell, creating a gel containing paliperidone that is then pushed out through the tablet orifice. The biologically inert components of the tablet remain intact during gastrointestinal transit and are eliminated in the stool as a tablet shell, along with insoluble core components.

12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

Paliperidone is the major active metabolite of risperidone. The mechanism of action of paliperidone in schizophrenia is unclear. However, the drug’s therapeutic effect in schizophrenia could be mediated through a combination of central dopamine Type 2 (D2 ) and serotonin Type 2 (5HT2A ) receptor antagonism.

12.2 Pharmacodynamics

In vitro, paliperidone acts as an antagonist at the central dopamine Type 2 (D2 ) and serotonin Type 2 (5HT2A ) receptors, with binding affinities (Ki values) of 1.6nM to 2.8 nM for D2 and 0.8 nM to 1.2 nM for 5HT2A receptors. Paliperidone is also active as an antagonist at the α1 and α2 adrenergic receptors and H1 histaminergic receptors, which may explain some of the other effects of the drug. Paliperidone has no affinity for cholinergic muscarinic or β1 — and β2 -adrenergic receptors. The pharmacological activity of the (+)- and (-)- paliperidone enantiomers is qualitatively and quantitatively similar in vitro.

12.3 Pharmacokinetics

Following a single dose, the plasma concentrations of paliperidone gradually rise to reach peak plasma concentration (Cmax ) approximately 24 hours after dosing. The pharmacokinetics of paliperidone following paliperidone extended-release tablets administration are dose-proportional within the available dose range. The terminal elimination half-life of paliperidone is approximately 23 hours.

Steady-state concentrations of paliperidone are attained within 4 to 5 days of dosing with paliperidone extended-release tablets in most subjects. The mean steady-state peak:trough ratio for a paliperidone extended-release tablets dose of 9 mg was 1.7 with a range of 1.2 to 3.1.

Following administration of paliperidone extended-release tablets, the (+) and (-) enantiomers of paliperidone interconvert, reaching an AUC (+) to (-) ratio of approximately 1.6 at steady state.

Absorption and Distribution

The absolute oral bioavailability of paliperidone following paliperidone extended-release tablets administration is 28%.

Administration of a 12 mg paliperidone extended-release tablet to healthy ambulatory subjects with a standard high-fat/high-caloric meal gave mean Cmax and AUC values of paliperidone that were increased by 60% and 54%, respectively, compared with administration under fasting conditions. Clinical trials establishing the safety and efficacy of paliperidone extended-release tablets were carried out in subjects without regard to the timing of meals. While paliperidone extended-release tablets can be taken without regard to food, the presence of food at the time of paliperidone extended-release tablets administration may increase exposure to paliperidone [see Dosage and Administration (2.3)].

Based on a population analysis, the apparent volume of distribution of paliperidone is 487 L. The plasma protein binding of racemic paliperidone is 74%.

Metabolism and Elimination

Although in vitro studies suggested a role for CYP2D6 and CYP3A4 in the metabolism of paliperidone, in vivo results indicate that these isozymes play a limited role in the overall elimination of paliperidone [see Drug Interactions (7)].

One week following administration of a single oral dose of 1 mg immediate-release 14 C-paliperidone to 5 healthy volunteers, 59% (range 51% to 67%) of the dose was excreted unchanged into urine, 32% (26% to 41%) of the dose was recovered as metabolites, and 6% to 12% of the dose was not recovered. Approximately 80% of the administered radioactivity was recovered in urine and 11% in the feces. Four primary metabolic pathways have been identified in vivo , none of which could be shown to account for more than 10% of the dose: dealkylation, hydroxylation, dehydrogenation, and benzisoxazole scission.

Population pharmacokinetic analyses found no difference in exposure or clearance of paliperidone between extensive metabolizers and poor metabolizers of CYP2D6 substrates.

Special Populations

Renal Impairment

The dose of paliperidone extended-release tablets should be reduced in patients with moderate or severe renal impairment [see Dosage and Administration (2.5)]. The disposition of a single dose paliperidone 3 mg extended-release tablet was studied in adult subjects with varying degrees of renal function. Elimination of paliperidone decreased with decreasing estimated creatinine clearance. Total clearance of paliperidone was reduced in subjects with impaired renal function by 32% on average in mild (CrCl = 50 mL/min to < 80 mL/min), 64% in moderate (CrCl = 30 mL/min to < 50 mL/min), and 71% in severe (CrCl = 10 mL/min to < 30 mL/min) renal impairment, corresponding to an average increase in exposure (AUCinf ) of 1.5 fold, 2.6 fold, and 4.8 fold, respectively, compared to healthy subjects. The mean terminal elimination half-life of paliperidone was 24 hours, 40 hours, and 51 hours in subjects with mild, moderate, and severe renal impairment, respectively, compared with 23 hours in subjects with normal renal function (CrCl ≥ 80 mL/min).

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