When should plasma levels be checked for Perseris (risperidone)?

Plasma Level Monitoring for Perseris (Risperidone Long-Acting Injection)

Blood for plasma level monitoring of Perseris (risperidone) should be collected after at least 5 drug half-lives (approximately 1 week) of stable dosing, immediately before the next scheduled injection, and when clinically indicated due to treatment failure or side effects. 1

When to Check Plasma Levels for Perseris

Timing of Sample Collection

• Collect blood samples at steady-state conditions (after at least 5 drug half-lives)
• For Perseris, this means approximately 1 week after stable dosing
• Draw blood immediately before the next scheduled injection (trough level)
• This timing provides the most consistent and interpretable results 1

Clinical Indications for Plasma Level Monitoring

1. Suspected non-compliance with treatment regimen
2. Inadequate clinical response despite appropriate dosing
3. Unexpected adverse effects at standard doses
4. Drug interactions with medications that may affect risperidone metabolism
5. Special populations:
   • Elderly patients (>65 years)
   • Children and adolescents
   • Patients with hepatic or renal impairment
   • Pregnant or lactating women 1

Interpreting Risperidone Plasma Levels

When interpreting plasma levels for risperidone, both the parent compound and its active metabolite (9-hydroxyrisperidone) should be measured, as both contribute to the clinical effect 2.

The combined concentration of risperidone and 9-hydroxyrisperidone provides the most clinically relevant information since:

• Risperidone is extensively metabolized in the liver through CYP2D6
• The active metabolite has similar pharmacological activity to the parent compound
• Individual variations in metabolism can affect the ratio of parent drug to metabolite 2, 3

Special Considerations

Genetic Polymorphisms

• CYP2D6 genetic polymorphisms can significantly affect risperidone metabolism
• About 6-8% of Caucasians are "poor metabolizers" with reduced CYP2D6 activity
• These patients may have higher risperidone and lower 9-hydroxyrisperidone levels
• Consider pharmacogenetic testing in cases of unexpected plasma levels or unusual response 1, 2

Drug Interactions

• Monitor plasma levels when adding or removing medications that:
  • Inhibit CYP2D6 (e.g., quinidine, fluoxetine, paroxetine)
  • Induce hepatic enzymes (e.g., carbamazepine, phenytoin, rifampin)
• These interactions can significantly alter the combined concentrations of risperidone and its active metabolite 2

Common Pitfalls to Avoid

1. Incorrect timing of blood draw: Collecting samples too soon after dose adjustment or at inconsistent times can lead to misleading results
2. Failure to measure both parent compound and active metabolite: Both contribute to clinical effect
3. Not considering genetic variations: CYP2D6 polymorphisms significantly impact metabolism
4. Overlooking drug interactions: Concomitant medications can alter risperidone metabolism
5. Relying solely on plasma levels: Clinical response should always guide treatment decisions alongside plasma level data 1

Remember that therapeutic drug monitoring is a tool to optimize treatment, but clinical judgment remains essential in interpreting results and making treatment decisions.