Significant difficulty or fears withdrawing SSRI/SNRI

Antidepressants: Quality prescribing - a guide for improvement
Scottish Government Effective Prescribing & Therapeutics Division
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For a very small minority of individuals, slower graduated reduction may be appropriate. For example, where standard reduction and/or discontinuing/withdrawing SSRI/SNRI has been unsuccessful. This approach will help flatten the reductions in plasma drug concentrations at lower doses (See chart below).

First, reduce current antidepressant to standard dose as per SSRI or SNRI. Then convert to an approximate dose equivalent of fluoxetine 20mg/5ml liquid.

Fluoxetine 20mg is approximately dose equivalent* to:

  • Citalopram 20mg
  • Escitalopram 10mg
  • Fluvoxamine 50mg
  • Paroxetine 20mg
  • Sertraline 50mg
  • Duloxetine 30mg
  • Venlafaxine 75mg

*Approximate dose equivalents and switching considerations:18,49

Due to inter-patient variability and differing half-lives, this means that these are approximate dose equivalents, not exact equivalence. 

  • The drug and dose equivalents can never be exact and should be interpreted considering your clinical knowledge and the individual’s needs.
  • Drug interactions and drug-disease interactions should be considered prior to any switch in therapy.

 

For example, if switching paroxetine 20mg daily to fluoxetine 20mg daily, or paroxetine 10mg daily to fluoxetine 8mg daily (step 3 below). Switch by taking the last dose of paroxetine today, and then start the new dose of fluoxetine tomorrow at the same time of day.18,20 Agree on an appropriate rate of reduction e.g. weekly or monthly and time for face-to-face or telephone review follow-up.

 

Example dose reduction using fluoxetine liquid 20mg/5ml

Step mg/d ml/d

Step down

Difference (mg)
1 20 5  - 
2 12 3 8
3 8 2 4
4 4.8 1.2 3.2
5 3.2 0.8 1.6
6 1.6 0.4 1.6
7 0.8 0.2 0.8
8 0.4 0.1 0.4
9 Then stop 0 0.4

Note:

  • Steps: the rate of withdrawal will vary with individual needs e.g. weekly to four weekly reductions for some.
  • Citalopram 40mg/ml and escitalopram 20mg/ml liquid are not recommended due to the difficulty with accurately measuring small doses.
  • Sertraline liquid is not recommended as it is unlicensed in the UK, and individuals may experience oral numbness on their tongue and mouth due to the anaesthetic effects of non-tablet formulations
  • Table above adapted with consideration of Horowitz et al,152 Ruhe et al,153 Selvaraj et al,154 and The Maudsley Prescribing Guidelines in Psychiatry 14th edition.18

 

Fluoxetine hyperbolic dose reduction