What dose of venlafaxine extended‑release tablet is equivalent to the 37.5 mg extended‑release capsule the patient is taking daily?

Venlafaxine ER Capsule to Tablet Conversion

The 37.5 mg extended-release capsule and 37.5 mg extended-release tablet formulations of venlafaxine are bioequivalent and can be switched on a 1:1 basis—your patient should continue taking 37.5 mg daily of the tablet formulation. 1

Pharmacokinetic Basis for Direct Conversion

• Venlafaxine demonstrates linear, dose-proportional pharmacokinetics across the therapeutic range of 75–375 mg/day, meaning plasma concentrations increase proportionally with dose regardless of formulation. 1
• Both extended-release capsules and tablets are designed to deliver the same total drug exposure over 24 hours, making them interchangeable at equivalent milligram doses. 1, 2, 3
• The therapeutic range for venlafaxine plus its active metabolite O-desmethylvenlafaxine is 195–400 ng/mL; a 37.5 mg dose of either formulation will produce comparable plasma levels within this range. 4, 1

Practical Switching Instructions

• Switch directly from 37.5 mg ER capsule to 37.5 mg ER tablet without any dose adjustment or titration period. 1
• Instruct the patient to take the tablet at the same time of day as the previous capsule to maintain steady plasma levels. 1, 5
• No washout period or overlap dosing is required because both formulations contain the same active drug with identical extended-release kinetics. 1, 5

Monitoring After the Switch

• Assess for any change in efficacy or tolerability at 1–2 weeks after switching formulations, as individual absorption characteristics may vary slightly between capsule and tablet matrices. 1, 5
• Monitor for recurrence of depressive or anxiety symptoms, which would indicate inadequate drug exposure with the new formulation. 5, 6
• Check for new or worsening adverse effects—particularly nausea, dizziness, dry mouth, or sweating—that might signal altered pharmacokinetics. 2, 3, 7

Critical Safety Considerations

• Measure baseline blood pressure before and after the formulation switch, as venlafaxine causes dose-dependent blood pressure elevations that may differ slightly between formulations. 8, 2, 3
• Patients with pre-existing hypertension or cardiovascular disease require closer monitoring during the first 2–4 weeks after switching. 8, 3
• Do not increase the dose above 37.5 mg without reassessing clinical response at 6–8 weeks, as the standard titration schedule calls for increases of 75 mg weekly only after establishing tolerability at lower doses. 1

When to Consider Dose Adjustment

• If the patient reports loss of therapeutic effect 2–4 weeks after switching to the tablet, verify adherence first, then consider increasing to 75 mg daily (the next standard dose increment). 1, 5
• If new adverse effects emerge that were not present with the capsule, consider splitting the 37.5 mg tablet dose into twice-daily administration (if the tablet is scored) or switching back to the capsule formulation. 7, 5
• Patients with renal impairment (eGFR < 90 mL/min) should have their dose reduced by 50% regardless of formulation; if this patient has renal dysfunction, the 37.5 mg dose may already be appropriate. 8