Wellbutrin SR Is a Sustained-Release Formulation
Yes, Wellbutrin SR (bupropion sustained-release) is a slow-release formulation designed for twice-daily administration. 1, 2, 3
Formulation Characteristics
Wellbutrin SR uses a wax-matrix vehicle for slow release, distinguishing it from the immediate-release formulation that requires three-times-daily dosing. 4 The SR formulation is bioequivalent to immediate-release bupropion in terms of total systemic exposure, but delivers the medication more gradually throughout the day. 2, 3
Dosing Schedule
The American College of Clinical Pharmacology recommends Wellbutrin SR be administered as 150 mg twice daily (total 300 mg/day) for major depressive disorder, with an initial titration period of 150 mg once daily for 3–4 days. 5, 6
The second dose should be taken before 3 PM to minimize insomnia risk, as bupropion has activating properties. 5
For smoking cessation, the standard regimen is 150 mg once daily for 3 days, then 150 mg twice daily (300 mg total), beginning 1–2 weeks before the target quit date. 5
Pharmacokinetic Profile
The SR formulation begins to act approximately 90 minutes after ingestion (compared with 30 minutes for immediate-release), and its plasma level peak occurs at 3 hours—1 hour later than the standard preparation. 4 This delayed onset and lower peak plasma concentration result from the wax-matrix slow-release mechanism. 4
Bupropion SR produces a gradually decreasing plasma concentration after its 3-hour peak, which may explain why some clinicians find it less immediately effective than immediate-release formulations for certain patients. 4
Comparison with Other Formulations
Wellbutrin XL (extended-release) is administered once daily (typically 300 mg in the morning), representing an even longer-duration formulation than SR. 5, 1
All three bupropion formulations—immediate-release (IR), sustained-release (SR), and extended-release (XL)—are bioequivalent in terms of total systemic exposure to bupropion, but differ in their release kinetics and dosing frequency. 2, 3
The maximum dose for SR formulation is 400 mg per day, compared with 450 mg per day for XL. 5, 6
Clinical Advantages of SR Formulation
The SR formulation offers improved compliance over immediate-release bupropion by reducing dosing frequency from three times daily to twice daily, while maintaining comparable efficacy and tolerability. 2, 3, 7
Wellbutrin SR was as effective as SSRIs in treating major depressive disorder, with the advantage of significantly lower rates of sexual dysfunction and somnolence. 2, 3