What is the difference between Wellbutrin (bupropion) SR (Sustained Release) and ER (Extended Release)?

Differences Between Wellbutrin SR and XL (Extended Release)

The main difference between Wellbutrin SR (Sustained Release) and XL (Extended Release) is their release mechanism and dosing frequency: SR is taken twice daily while XL is taken once daily, with both formulations being bioequivalent in terms of systemic exposure to bupropion.

Key Differences in Formulations

• Wellbutrin SR (Sustained Release) is administered twice daily, typically 150 mg twice daily for a total of 300 mg/day 1, 2
• Wellbutrin XL (Extended Release) is administered once daily in the morning, typically 300 mg once daily 1, 3
• Both formulations are bioequivalent in terms of systemic exposure to bupropion 4, 2

Pharmacokinetic Differences

• Absorption of XL formulation is more prolonged compared to SR formulation (peak concentration time approximately 5 hours vs approximately 3 hours, respectively) 5
• SR formulation has a more rapid onset but shorter duration of action compared to XL 2
• The extended-release mechanism in XL allows for more consistent blood levels throughout the 24-hour period 5

Clinical Considerations for Choosing Between Formulations

• XL offers better convenience with once-daily dosing, which may improve medication adherence 4, 2
• SR may be preferred for patients who need more flexible dosing due to side effects or who require dose adjustments for hepatic or renal impairment 1
• For patients with insomnia concerns, SR allows for timing the second dose earlier in the day (before 3 PM) to minimize sleep disturbances 1

Dosing Guidelines

• For Major Depressive Disorder (MDD):

  • SR: Start with 150 mg once daily for 3 days, then increase to 150 mg twice daily 1
  • XL: Start with 150 mg once daily in the morning, may increase to 300 mg once daily after 4 days 3

• For Smoking Cessation:

  • SR is the FDA-approved formulation at 150 mg twice daily, starting 1-2 weeks before quit date 1

Special Population Considerations

• For moderate to severe hepatic impairment:

  • XL: Maximum dose is 150 mg every other day 3
  • SR: Total daily dose should not exceed 150 mg daily (one tablet) 1

• For moderate to severe renal impairment:

  • Both formulations require dose reduction, typically by half of the standard dose 1, 3

Side Effect Profiles

• Both formulations have similar side effect profiles including headache, dry mouth, nausea, insomnia, and anxiety 2
• The risk of seizures exists with both formulations, necessitating gradual dose titration 3
• Rarely, patients may experience different tolerability between formulations - there are case reports of patients who developed hypersensitivity reactions to XL but later tolerated SR 6

Clinical Pearls

• When switching between formulations, the same total daily dose can generally be maintained 3
• Both formulations should be swallowed whole and not crushed, divided, or chewed 3
• Maximum doses differ slightly: SR maximum is 400 mg per day, while XL maximum is 450 mg per day 1
• Both formulations may be taken with or without food 3

Remember that the choice between SR and XL should be based on patient preference for dosing frequency, potential for adherence issues, and individual tolerability factors.