Risperidoneinteractions

Carbamazepine and other enzyme inducers decrease plasma concentrations of risperidone. Increase the risperidone dose up to double the patient's usual dose. Titrate slowly. Fluoxetine, paroxetine, and other CYP 2D6 enzyme inhibitors increase plasma concentrations of risperidone. Reduce the initial dose. Do not exceed a final dose of 8 mg per day of risperidone.

7.1 Pharmacokinetic-related

Interactions The dose of risperidone should be adjusted when used in combination with CYP2D6 enzyme inhibitors (e.g., fluoxetine, and paroxetine) and enzyme inducers (e.g., carbamazepine). Dose adjustment is not recommended for risperidone when co-administered with ranitidine, cimetidine, amitriptyline, or erythromycin. Table 18. Summary of Effect of Coadministered Drugs on Exposure to Active Moiety (Risperidone + 9-Hydroxy-Risperidone) in Healthy Subjects or Patients with Schizophrenia Coadministered Drug Dosing Schedule Effect on Active Moiety (Risperidone + 9-Hydroxy-Risperidone (Ratio Change relative to reference ) Risperidone Dose Recommendation Coadministered Drug Risperidone AUC C max Enzyme (CYP2D6) Inhibitors Fluoxetine 20 mg/day 2 or 3 mg twice daily 1.4 1.5 Re-evaluate dosing. Do not exceed 8 mg/day Paroxetine 10 mg/day 4 mg/day 1.3 - Re-evaluate dosing. Do not exceed 8 mg/day 20 mg/day 4 mg/day 1.6 - 40 mg/day 4 mg/day 1.8 - Enzyme (CYP3A/ PgP inducers) Inducers Carbamazepine 573 ± 168 mg/day 3 mg twice daily 0.51 0.55 Titrate dose upwards. Do not exceed twice the patient's usual dose Enzyme (CYP3A) Inhibitors Ranitidine 150 mg twice daily 1 mg single dose 1.2

1.4 Dose adjustment not needed

Cimetidine 400 mg twice daily 1 mg single dose 1.1

1.3 Dose adjustment not needed

Erythromycin 500 mg four times daily 1 mg single dose 1.1

0.94 Dose adjustment not needed

Other Drugs Amitriptyline 50 mg twice daily 3 mg twice daily 1.2

1.1 Dose adjustment not needed

Effect of Risperidone on Other Drugs Lithium Repeated oral doses of risperidone (3 mg twice daily) did not affect the exposure (AUC) or peak plasma concentrations (C max ) of lithium (n=13). Dose adjustment for lithium is not recommended. Valproate Repeated oral doses of 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 risperidone. Dose adjustment for valproate is not recommended. Digoxin Risperidone (0.25 mg twice daily) did not show a clinically relevant effect on the pharmacokinetics of digoxin. Dose adjustment for digoxin is not recommended.

7.2 Pharmacodynamic-related

Interactions Centrally Acting Drugs and Alcohol Given the primary CNS effects of risperidone, caution should be used when risperidone is taken in combination with other centrally-acting drugs and alcohol. Drugs with Hypotensive Effects Because of its potential for inducing hypotension, risperidone may enhance the hypotensive effects of other therapeutic agents with this potential. Levodopa and Dopamine Agonists Risperidone may antagonize the effects of levodopa and dopamine agonists. 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 and methylphenidate. Clozapine Chronic administration of clozapine with risperidone may decrease the clearance of risperidone.