Conversion from Bupropion SR 200mg Twice Daily to XL 300mg Once Daily
When converting from bupropion SR 200mg twice daily to bupropion XL 300mg once daily, the correct conversion is to use bupropion XL 300mg once daily for a total daily dose of 300mg, not 400mg. 1
Correct Dose Conversion
The appropriate conversion from bupropion SR (sustained-release) to bupropion XL (extended-release) follows these principles:
- Bupropion SR 200mg twice daily equals a total daily dose of 400mg
- When converting to XL formulation, the recommended approach is to reduce the total daily dose by approximately 25%
- Therefore, 400mg SR daily should convert to 300mg XL daily
Pharmacokinetic Considerations
The difference in conversion is based on the pharmacokinetic properties of the different formulations:
- SR formulation: Peaks twice daily with more fluctuation in blood levels
- XL formulation: Provides more consistent blood levels throughout 24 hours with a single peak
- The smoother pharmacokinetic profile of XL allows for lower total daily dosing while maintaining efficacy
Evidence-Based Rationale
According to the American Family Physician guidelines 1, bupropion dosing should be carefully managed:
- Initial dosing for bupropion (Wellbutrin) is typically 37.5mg every morning, then increased by 37.5mg every 3 days
- Maximum recommended dose is 150mg twice daily
- When converting between formulations, dose adjustments are necessary to maintain therapeutic effect while minimizing side effects
Clinical Implications
Converting at a 1:1 ratio (400mg SR to 400mg XL) could potentially:
- Increase risk of side effects including insomnia, agitation, and seizures
- Exceed the recommended therapeutic range for the XL formulation
- Provide unnecessarily high blood levels due to the different release mechanisms
Similar Conversion Principles in Other Medications
This principle of dose reduction when converting from multiple daily doses to once-daily extended-release formulations is seen in other medications as well:
- Tacrolimus conversion from twice-daily to once-daily formulations often requires dose adjustments after conversion 2, 3
- Diltiazem SR once-daily dosing provides 24-hour efficacy at lower total daily doses than multiple daily dosing 4
Monitoring After Conversion
After converting from SR to XL formulation:
- Monitor for clinical response
- Watch for side effects including insomnia, agitation, headache
- Ensure the patient takes the XL formulation in the morning to minimize risk of insomnia
- If response is inadequate, dose can be adjusted after appropriate evaluation
Remember that the extended-release formulation should not be crushed or chewed as this would defeat the purpose of the controlled release mechanism and potentially increase side effect risk.