Transitioning from Immediate-Release to Extended-Release Lithium
Calculate the total daily dose (150mg + 300mg = 450mg), then administer this same total dose (450mg) as extended-release lithium once daily at bedtime, without any dose reduction. 1
Conversion Strategy
- Use a 1:1 dose conversion when switching from immediate-release to extended-release lithium formulations, maintaining the total daily dose of 450mg 1, 2
- Administer the entire 450mg dose as a single evening dose to optimize tolerability and compliance 2, 3, 4
- Extended-release formulations reach peak plasma concentrations at 4-5 hours (versus 1-2 hours for immediate-release), resulting in 30-50% lower peak levels while maintaining similar overall drug exposure 2
Timing and Administration
- Switch directly from the immediate-release regimen to extended-release without any washout period or overlap 1
- Give the extended-release dose at bedtime (replacing the previous 300mg bedtime dose timing) to minimize awareness of transient peak-related side effects 2, 4
- Single daily dosing has been shown to reduce urinary frequency and polyuria compared to divided dosing, while maintaining equivalent efficacy 5, 4
Monitoring Requirements
- Check serum lithium level 12 hours post-dose after 5-7 days to ensure therapeutic range of 0.6-1.2 mEq/L for maintenance therapy 1
- With extended-release preparations, target the upper end of the therapeutic range (0.8-1.0 mEq/L) rather than 0.6-0.8 mEq/L used for immediate-release formulations, due to the lower peak concentrations 2
- Monitor twice weekly initially until stable, then at least every 2 months during maintenance 1
- Baseline and ongoing monitoring should include renal function tests, thyroid function tests, and serum calcium every 3-6 months 6
Critical Safety Considerations
- Do not split extended-release tablets, as this destroys the controlled-release mechanism and creates unpredictable absorption patterns that make therapeutic monitoring unreliable 7
- Watch for early toxicity signs including tremor, nausea, diarrhea, and polyuria, which can occur at levels ≥1.5 mEq/L 6
- Elderly patients and those with renal impairment (GFR <60 mL/min/1.73 m²) may require dose adjustments, though this patient's 450mg total daily dose is already relatively low 7, 1
Expected Outcomes
- Equivalent antimanic and mood-stabilizing efficacy compared to divided dosing 5, 3
- Potentially improved compliance due to simplified once-daily regimen 3, 4
- Reduced urinary frequency and polyuria compared to twice-daily dosing 5, 4
- Lower peak plasma concentrations may reduce acute side effects like tremor and gastrointestinal upset 2, 5