What is the recommended dosing strategy when switching from Wellbutrin (bupropion) XL to Wellbutrin (bupropion) SR?

Switching from Wellbutrin XL to Wellbutrin SR

When switching from Wellbutrin XL to Wellbutrin SR, maintain the same total daily dose but divide it into two administrations: if taking 300 mg XL once daily, switch to 150 mg SR twice daily. 1

Direct Switching Strategy

The FDA label explicitly states that when switching between bupropion formulations, you should "give the same total daily dose when possible." 1 This means:

• 300 mg XL once daily → 150 mg SR twice daily (same 300 mg total) 1
• 150 mg XL once daily → 150 mg SR once daily (though SR is typically dosed twice daily for depression, this maintains the same total dose) 2

No tapering or titration is required when switching between formulations at equivalent total daily doses. 1 The formulations are bioequivalent in terms of systemic exposure to bupropion, meaning they deliver the same amount of drug to your system despite different release mechanisms. 3, 4

Timing Considerations

• Administer the second SR dose before 3 p.m. to minimize insomnia risk 2
• The SR formulation reaches peak concentration (T_max) at approximately 3 hours, compared to 5 hours for XL 4
• Both formulations can be taken with or without food 1

Key Pharmacokinetic Differences

While the formulations are bioequivalent, understand these absorption differences:

• XL formulation: Prolonged absorption with T_max at approximately 5 hours, designed for once-daily dosing 4
• SR formulation: Faster absorption with T_max at approximately 3 hours, designed for twice-daily dosing 4
• Both achieve similar steady-state concentrations of bupropion and its active metabolites (hydroxybupropion, threohydrobupropion, erythrohydrobupropion) 4

Maximum Dose Limits

Be aware that maximum doses differ between formulations:

• SR maximum: 400 mg per day (200 mg twice daily) 2, 5
• XL maximum: 450 mg per day 2, 1

This difference exists to minimize seizure risk, which is dose-dependent. 1, 5

Special Population Adjustments

If your patient has hepatic or renal impairment, the same dose reductions apply regardless of formulation:

• Moderate to severe hepatic impairment: Maximum 150 mg daily (or 150 mg every other day for severe impairment) 2, 1
• Moderate to severe renal impairment (GFR <90 mL/min): Reduce total daily dose by half 2, 1

Common Pitfalls to Avoid

• Do not crush, divide, or chew SR tablets - this destroys the sustained-release mechanism and increases seizure risk 1
• Do not exceed 200 mg per single SR dose - the maximum single dose for SR is 200 mg to minimize seizure risk, whereas XL can be given as 300 mg once daily 1
• Do not assume once-daily SR dosing is equivalent to XL - while 150 mg once daily of either formulation delivers the same total dose, SR is FDA-approved for twice-daily dosing for depression treatment 2, 1