Risperidoneinteractions

The interactions of Risperidone for Extended-Release Injectable Suspension with coadministration of other drugs have not been systematically evaluated. The drug interaction data provided in this section is based on studies with oral risperidone. Due to CNS effects, use caution when administering with other centrally-acting drugs. Avoid alcohol. Due to hypotensive effects, hypotensive effects of other drugs with this potential may be enhanced. Effects of levodopa and dopamine agonists may be antagonized. Cimetidine and ranitidine increase the bioavailability of risperidone. Clozapine may decrease clearance of risperidone. Fluoxetine and paroxetine increase plasma concentrations of risperidone. Carbamazepine and other enzyme inducers decrease plasma concentrations of risperidone.

7.1 Centrally-Acting

Drugs and Alcohol Given the primary CNS effects of risperidone, caution should be used when Risperidone for Extended-Release Injectable Suspension is administered in combination with other centrally-acting drugs or alcohol.

7.2 Drugs with

Hypotensive Effects Because of its potential for inducing hypotension, Risperidone for Extended-Release Injectable Suspension may enhance the hypotensive effects of other therapeutic agents with this potential.

7.3 Levodopa and

Dopamine Agonists Risperidone for Extended-Release Injectable Suspension may antagonize the effects of levodopa and dopamine agonists.

7.4 Amitriptyline

Amitriptyline did not affect the pharmacokinetics of risperidone or of risperidone and 9-hydroxyrisperidone combined following concomitant administration with oral risperidone.

7.5 Cimetidine and

Ranitidine Cimetidine and ranitidine increased the bioavailability of oral risperidone by 64% and 26%, respectively. However, cimetidine did not affect the AUC of risperidone and 9-hydroxyrisperidone combined, whereas ranitidine increased the AUC of risperidone and 9-hydroxyrisperidone combined by 20%.

7.6 Methylphenidate

Concomitant use with methylphenidate, when there is change in dosage of either medication, may increase the risk of extrapyramidal symptoms (EPS). Monitor for symptoms of EPS with concomitant use of Risperidone for Extended-Release Injectable Suspension and methylphenidate.

7.7 Clozapine

Chronic administration of clozapine with risperidone may decrease the clearance of risperidone.

7.8 Lithium

Repeated doses of oral risperidone (3 mg twice daily) did not affect the exposure (AUC) or peak plasma concentrations (C max ) of lithium (N=13).

7.9 Valproate

Repeated doses of oral risperidone (4 mg once daily) did not affect the pre-dose or average plasma concentrations and exposure (AUC) of valproate (1000 mg/day in three divided doses) compared to placebo (N=21). However, there was a 20% increase in valproate peak plasma concentration (C max ) after concomitant administration of oral risperidone.

7.10 Digoxin

Oral risperidone (0.25 mg twice daily) did not show a clinically relevant effect on the pharmacokinetics of digoxin.

7.11 Topiramate

Oral risperidone administered at doses from 1 to 6 mg/day concomitantly with topiramate 400 mg/day resulted in a 23% decrease in risperidone C max and a 33% decrease in risperidone AUC 0-12 hour at steady state. Minimal reductions in the exposure to risperidone and 9-hydroxyrisperidone combined, and no change for 9-hydroxyrisperidone were observed. This interaction is unlikely to be of clinical significance. There was no clinically relevant effect of oral risperidone on the pharmacokinetics of topiramate.

7.12 Drugs That

Inhibit CYP 2D6 and Other CYP Isozymes Risperidone is metabolized to 9-hydroxyrisperidone by CYP 2D6, an enzyme that is polymorphic in the population and that can be inhibited by a variety of psychotropic and other drugs. Drug interactions that reduce the metabolism of risperidone to 9-hydroxyrisperidone would increase the plasma concentrations of risperidone and lower the concentrations of 9-hydroxyrisperidone. Analysis of clinical studies involving a modest number of poor metabolizers (n≅70 patients) does not suggest that poor and extensive metabolizers have different rates of adverse effects. No comparison of effectiveness in the two groups has been made. In vitro studies showed that drugs metabolized by other CYP isozymes, including 1A1, 1A2, 2C9, 2C19, and 3A4, are only weak inhibitors of risperidone metabolism. Fluoxetine and Paroxetine Fluoxetine (20 mg once daily) and paroxetine (20 mg once daily), CYP 2D6 inhibitors, have been shown to increase the plasma concentration of risperidone 2.5 to 2.8 fold and 3 to 9 fold respectively. Fluoxetine did not affect the plasma concentration of 9-hydroxyrisperidone. Paroxetine lowered the concentration of 9-hydroxyrisperidone by about 10%. When either concomitant fluoxetine or paroxetine is initiated or discontinued, the physician should re-evaluate the dose of Risperidone for Extended-Release Injectable Suspension. When initiation of fluoxetine or paroxetine is considered, patients may be placed on a lower dose of Risperidone for Extended-Release Injectable Suspension between 2 to 4 weeks before the planned start of fluoxetine or paroxetine therapy to adjust for the expected increase in plasma concentrations of risperidone. When fluoxetine or paroxetine is initiated in patients receiving the recommended dose of 25 mg Risperidone for Extended-Release Injectable Suspension, it is recommended to continue treatment with the 25 mg dose unless clinical judgment necessitates lowering the Risperidone for Extended-Release Injectable Suspension dose to 12.5 mg or necessitates interruption of Risperidone for Extended-Release Injectable Suspension treatment. When Risperidone for Extended-Release Injectable Suspension is initiated in patients already receiving fluoxetine or paroxetine, a starting dose of 12.5 mg can be considered. The efficacy of the 12.5 mg dose has not been investigated in clinical trials. The effects of discontinuation of concomitant fluoxetine or paroxetine therapy on the pharmacokinetics of risperidone and 9-hydroxyrisperidone have not been studied. Erythromycin There were no significant interactions between oral risperidone and erythromycin.

7.13 Carbamazepine and

Other CYP 3A4 Enzyme Inducers Carbamazepine coadministration with oral risperidone decreased the steady-state plasma concentrations of risperidone and 9-hydroxyrisperidone by about 50%. Plasma concentrations of carbamazepine did not appear to be affected. Coadministration of other known CYP 3A4 enzyme inducers (e.g., phenytoin, rifampin, and phenobarbital) with risperidone may cause similar decreases in the combined plasma concentrations of risperidone and 9-hydroxyrisperidone, which could lead to decreased efficacy of Risperidone for Extended-Release Injectable Suspension treatment. At the initiation of therapy with carbamazepine or other known hepatic enzyme inducers, patients should be closely monitored during the first 4 to 8 weeks, since the dose of Risperidone for Extended-Release Injectable Suspension may need to be adjusted. A dose increase, or additional oral risperidone, may need to be considered. On discontinuation of carbamazepine or other CYP 3A4 hepatic enzyme inducers, the dosage of Risperidone for Extended-Release Injectable Suspension should be re-evaluated and, if necessary, decreased. Patients may be placed on a lower dose of Risperidone for Extended-Release Injectable Suspension between 2 to 4 weeks before the planned discontinuation of carbamazepine or other CYP 3A4 enzyme inducers to adjust for the expected increase in plasma concentrations of risperidone plus 9-hydroxyrisperidone. For patients treated with the recommended dose of 25 mg Risperidone for Extended-Release Injectable Suspension and discontinuing from carbamazepine or other CYP 3A4 enzyme inducers, it is recommended to continue treatment with the 25 mg dose unless clinical judgment necessitates lowering the Risperidone for Extended-Release Injectable Suspension dose to 12.5 mg or necessitates interruption of Risperidone for Extended-Release Injectable Suspension treatment. The efficacy of the 12.5 mg dose has not been investigated in clinical trials

7.14 Drugs Metabolized by CYP 2D6

In vitro studies indicate that risperidone is a relatively weak inhibitor of CYP 2D6. Therefore, Risperidone for Extended-Release Injectable Suspension is not expected to substantially inhibit the clearance of drugs that are metabolized by this enzymatic pathway. In drug interaction studies, oral risperidone did not significantly affect the pharmacokinetics of donepezil and galantamine, which are metabolized by CYP 2D6.