Starting Dose of Venlafaxine XR After Fluoxetine Discontinuation
Start venlafaxine XR at 75 mg daily, not 37.5 mg, as the 37.5 mg dose is intended for tapering discontinuation rather than initial therapeutic dosing. 1
Rationale for 75 mg Starting Dose
The 75 mg dose is the established therapeutic starting dose for venlafaxine XR in depression and anxiety disorders, with clinical improvement evident as early as week 2 of treatment. 1, 2
The 37.5 mg dose serves a specific purpose: it is designed for gradual tapering when stopping treatment to minimize withdrawal symptoms, not as an initial therapeutic dose. 1
Research demonstrates that venlafaxine XR 75 mg once daily produces significant therapeutic response by week 2-4, with sustained efficacy when continued at this dose or increased to 150 mg if needed after 2 weeks. 2, 3
Dosing Algorithm After Fluoxetine Switch
Week 1 (washout complete): Start venlafaxine XR 75 mg once daily. 1, 2
Week 2-3: Assess response and tolerability:
- If inadequate response after 2 weeks, increase to 150 mg daily. 2, 4
- Target therapeutic range is 150-225 mg/day for most patients with anxiety, though 75-150 mg may be sufficient. 1
Week 4-6: An adequate trial requires 4-6 weeks at the target dose before determining efficacy. 1
Critical Monitoring Requirements
Baseline and ongoing monitoring must include:
- Blood pressure and pulse at baseline and during treatment, as venlafaxine causes sustained hypertension and increased heart rate in some patients. 1
- Height and weight monitoring. 1
- Watch for behavioral activation, agitation, hypomania, or mania. 1
- Monitor for suicidal thinking and behavior, particularly in patients through age 24 years, as venlafaxine may carry greater suicide risk than other SNRIs. 1
BMI Consideration
The patient's BMI of 30 does not require dose adjustment for venlafaxine, as dose reductions are only indicated for hepatic impairment (50% reduction) or renal impairment (25-50% reduction depending on severity). 1 Standard dosing applies.
Common Pitfall to Avoid
Do not start at 37.5 mg thinking it represents a "low and slow" approach. This dose lacks therapeutic efficacy and only prolongs the time to clinical response. The most common adverse event is nausea, which occurs primarily in the first 2 weeks regardless of starting dose, with low likelihood of developing thereafter. 2 Starting at 75 mg allows earlier therapeutic benefit while the nausea risk remains similar.