Switching from Wellbutrin SR to XL: Timing Recommendations
You should skip the SR dose at 1pm today and start the XL formulation tomorrow morning at 150mg, as taking both formulations within 24 hours creates unnecessary overlap and increases seizure risk due to excessive bupropion exposure. 1
Rationale for Waiting Until Tomorrow
Pharmacokinetic Considerations
- Bupropion SR has a half-life of approximately 21 hours, with its primary active metabolite hydroxybupropion also having a half-life of approximately 20 hours 2
- Taking an SR dose now would result in overlapping drug levels when you start XL tomorrow morning, potentially exceeding safe exposure limits 2
- The active metabolites (hydroxybupropion, threohydrobupropion, and erythrohydrobupropion) have half-lives ranging from 20-37 hours, meaning they persist well into the next day 2
Seizure Risk Management
- Bupropion lowers the seizure threshold, and the maximum daily dose should not exceed 450 mg to minimize this risk 1
- Overlapping formulations could inadvertently push total bupropion exposure above safe thresholds 1
- The seizure risk is dose-dependent and cumulative exposure matters 1, 2
Optimal Transition Strategy
Starting XL Tomorrow Morning
- Wellbutrin XL should be administered as a single 150mg dose in the morning 1
- Morning dosing leverages bupropion's activating properties and minimizes insomnia risk 1
- The XL formulation reaches peak concentration (Tmax) at approximately 5 hours, providing steady drug levels throughout the day 2
Formulation Equivalence
- All three bupropion formulations (IR, SR, and XL) are bioequivalent in terms of systemic exposure to bupropion 3
- The 150mg XL once daily provides comparable total drug exposure to 150mg SR twice daily 3, 2
- The primary difference is the absorption profile: XL provides more sustained release over 24 hours 4, 2
Common Pitfall to Avoid
Do not attempt to "bridge" between formulations by taking both on the same day. The extended half-lives of bupropion and its metabolites mean that skipping one dose will not result in any therapeutic gap, while taking both creates unnecessary risk 2.