Dose Conversion: Quetiapine 150 mg at Bedtime to Extended-Release
Convert quetiapine immediate-release (IR) 150 mg at bedtime to quetiapine extended-release (XR) 300 mg once daily at bedtime.
Conversion Rationale
The FDA-approved dosing for quetiapine XR establishes that the total daily dose of immediate-release formulation equals the total daily dose of extended-release formulation 1. Since you are currently taking 150 mg IR once daily at bedtime, the equivalent XR dose would be 150 mg once daily. However, pharmacokinetic studies demonstrate that quetiapine XR 300 mg once daily provides equivalent 24-hour drug exposure (AUC) to quetiapine IR 150 mg twice daily (total 300 mg/day) 2.
Key Pharmacokinetic Differences
When comparing IR versus XR formulations at equivalent total daily doses 2:
- AUC (total drug exposure): Essentially equivalent between formulations
- Cmax (peak concentration): XR produces ~13% lower peak levels than IR
- Tmax (time to peak): XR reaches peak at 5 hours vs. 2 hours for IR
- Cmin (trough levels): Nearly identical between formulations (95.3 vs 96.5 ng/mL)
Recommended Conversion
For quetiapine IR 150 mg at bedtime → Switch to quetiapine XR 150 mg once daily at bedtime
This maintains the same total daily dose. The XR formulation will provide:
- More stable plasma concentrations over 24 hours
- Reduced peak-related side effects (sedation, orthostatic hypotension)
- Equivalent therapeutic efficacy
Clinical Considerations
If the patient requires twice-daily IR dosing (e.g., 150 mg BID = 300 mg total daily), then convert to quetiapine XR 300 mg once daily 2.
The FDA label specifies that quetiapine XR can be taken with or without food, and the extended-release tablets must be swallowed whole—not divided, crushed, or chewed 1.
Important Caveats
- Geriatric patients: Consider starting at lower doses (50 mg/day XR) with slower titration 1
- Hepatic impairment: May require dose reduction (starting at 25 mg/day) with careful titration 1
- Monitor for metabolic changes, orthostatic hypotension, and QTc prolongation regardless of formulation 1
The conversion is straightforward: match the total daily dose between formulations, recognizing that XR provides smoother pharmacokinetics with once-daily dosing convenience.