Switching antidepressant (SSRIs to serotonin and noradrenaline reuptake inhibitors (SNRIs) (e.g. duloxetine or venlafaxine)) in adults

SSRIs to serotonin and noradrenaline reuptake inhibitors (SNRIs)

From all except fluoxetine

Direct switch

• a direct switch, i.e. stopping one antidepressant and then starting the new antidepressant the following day, is normally possible.

Additional caution when switching from paroxetine

• if switching from paroxetine, caution is required because it is a potent inhibitor of the liver enzyme CYP2D6 which is involved in the metabolism of duloxetine and venlafaxine
  • there is therefore a risk of raised duloxetine or venlafaxine levels in the body when they are administered together.

Additional caution when switching from fluvoxamine

• if switching from fluvoxamine, caution is required because it is a potent inhibitor of the liver enzyme CYP1A2 which is involved in the metabolism of duloxetine
  • there is therefore a risk of raised duloxetine levels in the body when they are administered together.

From fluoxetine

Taper, washout and switch

• gradually reduce the dose of fluoxetine to 20mg daily and stop; wait 4 to 7 days before starting the SNRI
• clinicians should decide the duration of the washout period on a case-by-case basis

Fluoxetine may still cause medicine interactions 5 or 6 weeks after stopping, as fluoxetine and its active metabolite have a long half-life.

If switching from fluoxetine, caution is required as it is a potent inhibitor of the liver enzyme CYP2D6 which is involved in the metabolism of duloxetine and venlafaxine. There is therefore a risk of raised duloxetine or venlafaxine levels in the body when switching.

Reference:

• NHS Specialist Pharmacy Service (February 2023). SSRIs to other antidepressants: switching in adults