Risperidone .25 mg Tablet, 30-count — NDC 0615-8196-30 (Billing 00615-8196-30)

12 CLINICAL PHARMACOLOGY

12.1Mechanism of Action The mechanism of action of Risperidone, in schizophrenia, is unknown. However, it has been proposed that the drug's therapeutic activity in schizophrenia could be mediated through a combination of dopamine Type 2 (D 2 ) and serotonin Type 2 (5HT 2 ) receptor antagonism. The clinical effect from Risperidone results from the combined concentrations of risperidone and its major metabolite, 9-hydroxyrisperidone [see Clinical Pharmacology (12.3) ] .

Antagonism at receptors other than D 2 and 5HT 2 [see Clinical Pharmacology (12.1) ] may explain some of the other effects of Risperidone.

12.2Pharmacodynamics Risperidone is a selective monoaminergic antagonist with high affinity (Ki of 0.12 to 7.3 nM) for the serotonin Type 2 (5HT 2 ), dopamine Type 2 (D 2 ), α 1 and α 2 adrenergic, and H 1 histaminergic receptors. Risperidone acts as an antagonist at other receptors, but with lower potency. Risperidone has low to moderate affinity (Ki of 47 to 253 nM) for the serotonin 5HT 1C , 5HT 1D , and 5HT 1A receptors, weak affinity (Ki of 620 to 800 nM) for the dopamine D 1 and haloperidol-sensitive sigma site, and no affinity (when tested at concentrations >10 -5 M) for cholinergic muscarinic or β 1 and β 2 adrenergic receptors.

12.3Pharmacokinetics Absorption Risperidone is well absorbed. The absolute oral bioavailability of risperidone is 70% (CV=25%). The relative oral bioavailability of risperidone from a tablet is 94% (CV=10%) when compared to a solution.

Plasma concentrations of risperidone, its major metabolite, 9-hydroxyrisperidone, and risperidone plus 9-hydroxyrisperidone are dose proportional over the dosing range of 1 to 16 mg daily (0.5 to 8 mg twice daily). Following oral administration of solution or tablet, mean peak plasma concentrations of risperidone occurred at about 1 hour. Peak concentrations of 9-hydroxyrisperidone occurred at about 3 hours in extensive metabolizers, and 17 hours in poor metabolizers.

Steady-state concentrations of risperidone are reached in 1 day in extensive metabolizers and would be expected to reach steady-state in about 5 days in poor metabolizers. Steady-state concentrations of 9-hydroxyrisperidone are reached in 5–6 days (measured in extensive metabolizers). Food Effect Food does not affect either the rate or extent of absorption of risperidone.

Thus, Risperidone can be given with or without meals. Distribution Risperidone is rapidly distributed. The volume of distribution is 1–2 L/kg.

In plasma, risperidone is bound to albumin and α 1 -acid glycoprotein. The plasma protein binding of risperidone is 90%, and that of its major metabolite, 9-hydroxyrisperidone, is 77%. Neither risperidone nor 9-hydroxyrisperidone displaces each other from plasma binding sites.

High therapeutic concentrations of sulfamethazine (100 mcg/mL), warfarin (10 mcg/mL), and carbamazepine (10mcg/mL) caused only a slight increase in the free fraction of risperidone at 10 ng/mL and 9-hydroxyrisperidone at 50 ng/mL, changes of unknown clinical significance. Metabolism Risperidone is extensively metabolized in the liver. The main metabolic pathway is through hydroxylation of risperidone to 9-hydroxyrisperidone by the enzyme, CYP 2D6.

A minor metabolic pathway is through N -dealkylation. The main metabolite, 9-hydroxyrisperidone, has similar pharmacological activity as risperidone. Consequently, the clinical effect of the drug results from the combined concentrations of risperidone plus 9-hydroxyrisperidone.

CYP 2D6, also called debrisoquin hydroxylase, is the enzyme responsible for metabolism of many neuroleptics, antidepressants, antiarrhythmics, and other drugs. CYP 2D6 is subject to genetic polymorphism (about 6%–8% of Caucasians, and a very low percentage of Asians, have little or no activity and are "poor metabolizers") and to inhibition by a variety of substrates and some non-substrates, notably quinidine. Extensive CYP 2D6 metabolizers convert risperidone rapidly into 9-… [Excerpted — this section continues on DailyMed.]

12.1Mechanism of Action The mechanism of action of Risperidone, in schizophrenia, is unknown. However, it has been proposed that the drug's therapeutic activity in schizophrenia could be mediated through a combination of dopamine Type 2 (D 2 ) and serotonin Type 2 (5HT 2 ) receptor antagonism. The clinical effect from Risperidone results from the combined concentrations of risperidone and its major metabolite, 9-hydroxyrisperidone [see Clinical Pharmacology (12.3) ] .

Antagonism at receptors other than D 2 and 5HT 2 [see Clinical Pharmacology (12.1) ] may explain some of the other effects of Risperidone.

12.3Pharmacokinetics Absorption Risperidone is well absorbed. The absolute oral bioavailability of risperidone is 70% (CV=25%). The relative oral bioavailability of risperidone from a tablet is 94% (CV=10%) when compared to a solution.

Plasma concentrations of risperidone, its major metabolite, 9-hydroxyrisperidone, and risperidone plus 9-hydroxyrisperidone are dose proportional over the dosing range of 1 to 16 mg daily (0.5 to 8 mg twice daily). Following oral administration of solution or tablet, mean peak plasma concentrations of risperidone occurred at about 1 hour. Peak concentrations of 9-hydroxyrisperidone occurred at about 3 hours in extensive metabolizers, and 17 hours in poor metabolizers.

Steady-state concentrations of risperidone are reached in 1 day in extensive metabolizers and would be expected to reach steady-state in about 5 days in poor metabolizers. Steady-state concentrations of 9-hydroxyrisperidone are reached in 5–6 days (measured in extensive metabolizers). Food Effect Food does not affect either the rate or extent of absorption of risperidone.

Thus, Risperidone can be given with or without meals. Distribution Risperidone is rapidly distributed. The volume of distribution is 1–2 L/kg.

In plasma, risperidone is bound to albumin and α 1 -acid glycoprotein. The plasma protein binding of risperidone is 90%, and that of its major metabolite, 9-hydroxyrisperidone, is 77%. Neither risperidone nor 9-hydroxyrisperidone displaces each other from plasma binding sites.

High therapeutic concentrations of sulfamethazine (100 mcg/mL), warfarin (10 mcg/mL), and carbamazepine (10mcg/mL) caused only a slight increase in the free fraction of risperidone at 10 ng/mL and 9-hydroxyrisperidone at 50 ng/mL, changes of unknown clinical significance. Metabolism Risperidone is extensively metabolized in the liver. The main metabolic pathway is through hydroxylation of risperidone to 9-hydroxyrisperidone by the enzyme, CYP 2D6.

A minor metabolic pathway is through N -dealkylation. The main metabolite, 9-hydroxyrisperidone, has similar pharmacological activity as risperidone. Consequently, the clinical effect of the drug results from the combined concentrations of risperidone plus 9-hydroxyrisperidone.

CYP 2D6, also called debrisoquin hydroxylase, is the enzyme responsible for metabolism of many neuroleptics, antidepressants, antiarrhythmics, and other drugs. CYP 2D6 is subject to genetic polymorphism (about 6%–8% of Caucasians, and a very low percentage of Asians, have little or no activity and are "poor metabolizers") and to inhibition by a variety of substrates and some non-substrates, notably quinidine. Extensive CYP 2D6 metabolizers convert risperidone rapidly into 9-hydroxyrisperidone, whereas poor CYP 2D6 metabolizers convert it much more slowly.

Although extensive metabolizers have lower risperidone and higher 9-hydroxyrisperidone concentrations than poor metabolizers, the pharmacokinetics of risperidone and 9-hydroxyrisperidone combined, after single and multiple doses, are similar in extensive and poor metabolizers. Risperidone could be subject to two kinds of drug-drug interactions. First, inhibitors of CYP 2D6 interfere with conversion of risperidone to 9-hydroxyrisperidone [see Drug Interactions (7) ] .

This occurs with quinidine, giving essentially all recipients a risperidone pharmacokinetic profile typical of poor metabolizers. The therapeutic benefits and adverse effects of risperidone in patients receiving quinidine have not been evaluated, but observations in a modest number (n70) of poor metabolizers given Risperidone do not suggest important differences between poor and extensive metabolizers. Second, co-administration of known enzyme inducers (e.g., carbamazepine, phenytoin, rifampin, and phenobarbital) with Risperidone may cause a decrease in the combined plasma concentrations of risperidone and 9-hydroxyrisperidone [see Drug Interactions (7) ] .

It would also be possible for risperidone to interfere with met… [Excerpted — this section continues on DailyMed.]

12.2Pharmacodynamics Risperidone is a selective monoaminergic antagonist with high affinity (Ki of 0.12 to 7.3 nM) for the serotonin Type 2 (5HT 2 ), dopamine Type 2 (D 2 ), α 1 and α 2 adrenergic, and H 1 histaminergic receptors. Risperidone acts as an antagonist at other receptors, but with lower potency. Risperidone has low to moderate affinity (Ki of 47 to 253 nM) for the serotonin 5HT 1C , 5HT 1D , and 5HT 1A receptors, weak affinity (Ki of 620 to 800 nM) for the dopamine D 1 and haloperidol-sensitive sigma site, and no affinity (when tested at concentrations >10 -5 M) for cholinergic muscarinic or β 1 and β 2 adrenergic receptors.

14 CLINICAL STUDIES

14.1Schizophrenia Adults Short-Term Efficacy The efficacy of Risperidone in the treatment of schizophrenia was established in four short-term (4- to 8-week) controlled trials of psychotic inpatients who met DSM-III-R criteria for schizophrenia. Several instruments were used for assessing psychiatric signs and symptoms in these studies, among them the Brief Psychiatric Rating Scale (BPRS), a multi-item inventory of general psychopathology traditionally used to evaluate the effects of drug treatment in schizophrenia.

The BPRS psychosis cluster (conceptual disorganization, hallucinatory behavior, suspiciousness, and unusual thought content) is considered a particularly useful subset for assessing actively psychotic schizophrenic patients. A second traditional assessment, the Clinical Global Impression (CGI), reflects the impression of a skilled observer, fully familiar with the manifestations of schizophrenia, about the overall clinical state of the patient. In addition, the Positive and Negative Syndrome Scale (PANSS) and the Scale for Assessing Negative Symptoms (SANS) were employed.

The results of the trials follow: In a 6-week, placebo-controlled trial (n=160) involving titration of Risperidone in doses up to 10 mg/day (twice-daily schedule), Risperidone was generally superior to placebo on the BPRS total score, on the BPRS psychosis cluster, and marginally superior to placebo on the SANS. In an 8-week, placebo-controlled trial (n=513) involving 4 fixed doses of Risperidone (2 mg/day, 6 mg/day, 10 mg/day, and 16 mg/day, on a twice-daily schedule), all 4 Risperidone groups were generally superior to placebo on the BPRS total score, BPRS psychosis cluster, and CGI severity score; the 3 highest Risperidone dose groups were generally superior to placebo on the PANSS negative subscale.

The most consistently positive responses on all measures were seen for the 6 mg dose group, and there was no suggestion of increased benefit from larger doses. In an 8-week, dose comparison trial (n=1356) involving 5 fixed doses of (1 mg/day, 4 mg/day, 8 mg/day, 12 mg/day, and 16 mg/day, on a twice-daily schedule), the four highest Risperidone dose groups were generally superior to the 1 mg Risperidone dose group on BPRS total score, BPRS psychosis cluster, and CGI severity score. None of the dose groups were superior to the 1 mg group on the PANSS negative subscale.

The most consistently positive responses were seen for the 4 mg dose group. In a 4-week, placebo-controlled dose comparison trial (n=246) involving 2 fixed doses of Risperidone (4 and 8 mg/day on a once-daily schedule), both Risperidone dose groups were generally superior to placebo on several PANSS measures, including a response measure (>20% reduction in PANSS total score), PANSS total score, and the BPRS psychosis cluster (derived from PANSS). The results were generally stronger for the 8 mg than for the 4 mg dose group.

Long-Term Efficacy In a longer-term trial, 365 adult outpatients predominantly meeting DSM-IV criteria for schizophrenia and who had been clinically stable for at least 4 weeks on an antipsychotic medication were randomized to Risperidone (2–8 mg/day) or to an active comparator, for 1 to 2 years of observation for relapse. Patients receiving Risperidone experienced a significantly longer time to relapse over this time period compared to those receiving the active comparator. Pediatrics The efficacy of Risperidone in the treatment of schizophrenia in adolescents aged 13–17 years was demonstrated in two short-term (6 and 8 weeks), double-blind controlled trials.

All patients met DSM-IV diagnostic criteria for schizophrenia and were experiencing an acute episode at time of enrollment. In the first trial (study #1), patients were randomized into one of three treatment groups: Risperidone 1–3 mg/day (n = 55, mean modal dose = 2.6 mg), Risperidone 4–6 mg/day (n = 51, mean modal dose = 5.3 mg), or placebo (n = 54). In the second trial (study #2), patien… [Excerpted — this section continues on DailyMed.]

13 NONCLINICAL TOXICOLOGY

13.1Carcinogenesis, Mutagenesis, Impairment of Fertility Carcinogenesis Carcinogenicity studies were conducted in Swiss albino mice and Wistar rats. Risperidone was administered in the diet at doses of 0.63 mg/kg, 2.5 mg/kg, and 10 mg/kg for 18 months to mice and for 25 months to rats. These doses are equivalent to approximately 2, 9, and 38 times the maximum recommended human dose (MRHD) for schizophrenia of 16 mg/day on a mg/kg basis or 0.2, 0.75, and 3 times the MRHD (mice) or 0.4, 1.5, and 6 times the MRHD (rats) on a mg/m 2 body surface basis.

A maximum tolerated dose was not achieved in male mice. There were statistically significant increases in pituitary gland adenomas, endocrine pancreas adenomas, and mammary gland adenocarcinomas. The table below summarizes the multiples of the human dose on a mg/m 2 (mg/kg) basis at which these tumors occurred.

Multiples of Maximum Human Dose in mg/m 2 (mg/kg) Tumor Type Species Sex Lowest Effect Level Highest No-Effect Level Pituitary adenomas mouse female 0.75 (9.4) 0.2 (2.4) Endocrine pancreas adenomas rat male 1.5 (9.4) 0.4 (2.4) Mammary gland adenocarcinomas mouse female 0.2 (2.4) none rat female 0.4 (2.4) none rat male 6.0 (37.5) 1.5 (9.4) Mammary gland neoplasm, Total rat male 1.5 (9.4) 0.4 (2.4) Antipsychotic drugs have been shown to chronically elevate prolactin levels in rodents. Serum prolactin levels were not measured during the risperidone carcinogenicity studies; however, measurements during subchronic toxicity studies showed that risperidone elevated serum prolactin levels 5–6 fold in mice and rats at the same doses used in the carcinogenicity studies.

An increase in mammary, pituitary, and endocrine pancreas neoplasms has been found in rodents after chronic administration of other antipsychotic drugs and is considered to be prolactin-mediated. The relevance for human risk of the findings of prolactin-mediated endocrine tumors in rodents is unknown [see Warnings and Precautions (5.6) ] . Mutagenesis No evidence of mutagenic or clastogenic potential for risperidone was found in the Ames gene mutation test, the mouse lymphoma assay, the in vitro rat hepatocyte DNA-repair assay, the in vivo micronucleus test in mice, the sex-linked recessive lethal test in Drosophila , or the chromosomal aberration test in human lymphocytes or Chinese hamster ovary cells.

Impairment of Fertility Risperidone (0.16 to 5 mg/kg) was shown to impair mating, but not fertility, in Wistar rats in three reproductive studies (two Segment I and a multigenerational study) at doses 0.1 to 3 times the maximum recommended human dose (MRHD) on a mg/m 2 body surface area basis. The effect appeared to be in females, since impaired mating behavior was not noted in the Segment I study in which males only were treated. In a subchronic study in Beagle dogs in which risperidone was administered orally at doses of 0.31 to 5 mg/kg, sperm motility and concentration were decreased at doses 0.6 to 10 times the MRHD on a mg/m 2 body surface area basis.

Dose-related decreases were also noted in serum testosterone at the same doses. Serum testosterone and sperm parameters partially recovered, but remained decreased after treatment was discontinued. A no-effect dose could not be determined in either rat or dog.

13.2Animal Toxicology Juvenile dogs were treated for 40 weeks with oral risperidone doses of 0.31, 1.25, or 5 mg/kg/day. Decreased bone length and density were observed with a no-effect dose of 0.31 mg/kg/day. This dose produced plasma AUC levels of risperidone plus its active metabolite paliperidone (9-hydroxy-risperidone) which were similar to those in children and adolescents receiving the maximum recommended human dose (MRHD) of 6 mg/day.

In addition, a delay in sexual maturation was seen at all doses in both males and females. The above effects showed little or no reversibility in females after a 12 week drug-free recovery period. In a study in which juvenile rats were treated wi… [Excerpted — this section continues on DailyMed.]