Converting Risperdal Consta to Oral Risperidone
When discontinuing Risperdal Consta (long-acting injection), continue the injection schedule and initiate oral risperidone at the time the next injection would have been due, using equivalent dosing based on the injection strength: 25 mg injection converts to 2-3 mg oral daily, 37.5 mg converts to 3-4 mg oral daily, and 50 mg converts to 4-6 mg oral daily. 1
Conversion Ratios Based on Research Evidence
The most rigorous pharmacokinetic study established these equivalent switching doses 1:
- 25 mg Consta every 2 weeks → 2-3 mg oral risperidone daily
- 37.5 mg Consta every 2 weeks → 3-4 mg oral risperidone daily
- 50 mg Consta every 2 weeks → 4-6 mg oral risperidone daily
These ratios are based on a 48-week randomized pharmacokinetic study that demonstrated bioequivalence between formulations while accounting for the sustained-release properties of the long-acting injection 1, 2.
Critical Timing Considerations
The key to successful conversion is understanding the pharmacokinetic profile of Risperdal Consta:
- Significant risperidone release from the microspheres begins 3 weeks after injection and continues for 7-8 weeks after the last dose 3, 2
- Steady-state plasma concentrations are reached after the fourth injection 3
- When converting from injection to oral, start oral risperidone at the time the next injection would be due (typically 2 weeks after the last injection) 3
Practical Conversion Algorithm
Step 1: Identify the current Consta dose (25,37.5, or 50 mg every 2 weeks) 1
Step 2: Calculate the equivalent oral dose using the conversion ratios above 1
Step 3: Initiate oral risperidone at the scheduled time of the next injection (do not start oral medication immediately after the last injection, as therapeutic levels persist) 3, 2
Step 4: Monitor for symptom stability using standardized assessments over the first 4-8 weeks, as plasma concentration fluctuations will be 32-42% higher with oral dosing compared to the long-acting formulation 2
Important Clinical Caveats
Patients on lower Consta doses (25 or 37.5 mg) showed increased relapse tendency when converted, suggesting these patients may benefit from the higher end of the oral dose range or closer monitoring 1. The long-acting formulation produces lower peak concentrations (25-32% lower) but more stable plasma levels than oral dosing, which may affect tolerability during conversion 2.
Formulation switching is generally well-tolerated: A study of 82 patients switching between oral formulations (compressed tablets to orally disintegrating tablets at equivalent doses) showed maintenance of effect with minimal side effects, suggesting dose-equivalent switches preserve clinical stability 4.
The oral formulation can be rapidly titrated if needed: Oral risperidone can be safely escalated by 1 mg every 6-8 hours up to 3 mg twice daily within 24 hours in acute settings, though this aggressive approach is typically unnecessary for stable patients converting from Consta 5.