During the management of depression in the clinical setting, a patient may request to swap from one antidepressant medicine to the next either due to an ineffective response, despite appropriate prescribing / use for a sufficient amount of time, or the side effect profile being too much to tolerate for that particular individual.
Naturally, switching from one drug to another in this particular field of medicine is not straightforward and the process needs a great deal of thought from the clinician / clinical team involved. Luckily, a number of support resources are available to guide prescribing practice and one such resource may be found at: https://www.sps.nhs.uk/wp-content/uploads/2019/10/UKMI_QA_How-do-you-switch-between-TCA-SSRI-related-antidepressants_update_Oct-2019.pdf. Here, mechanisms for switching between antidepressants are clearly outlined.
In brief, the clinician may choose to go for the ‘Direct Switch’ that simply involves moving from one drug to the next over the course of a day (i.e. Citalopram 20mg od to Duloxetine 60mg od, the next day), the ‘Gradual Withdrawal followed by the Switch’ that is essentially as listed (i.e. withdrawal over several weeks then new initiation) and finally the ‘Cross-Taping’ method whereby the patient receives two drugs with one decreasing and the other increasing within the same time frame. Three options, which to choose? See the table in the reference for guidance….
A further complication in all of this involves the nature of the drug and more precisely the half-life of the medication. I’m not going to explain the elimination half-life here, contact me if you need clarification. However, what I will say is that medication such as Fluoxetine and Vortioxetine have long half lives and as such last in the system for some time (e.g. 5 - 7 days). So, this must be accounted for if another SSRI is going to be initiated. This is so because if the two drugs cross over then serotonin syndrome may present….
This leads me nicely onto serotonin syndrome (SS)…..
Now, SS used to confuse me slightly back in the day when I was younger but quite honestly there is no need to be confused within this clinical manifestation. Put simply, it is too much serotonin in the brain. That is it. Too much of the “good stuff” in the brain. The reasons for the presentation of SS can be either additive effects between serotonergic ‘Drug A’ and ‘Drug B’ or the co-prescribing of drugs that give a serotonin-like response in the body. A good example of the former is the de-prescribing of Fluoxetine, with its long half-life, and the initiation of Sertraline as a switch over.
Typical signs of SS include:
Agitation
Confusion
Sweating
Fever
Abnormal body movements
Blood pressure changes (either increased or decreased BP)
Adverse gastrointestinal events (i.e. diarrhoea)
Diagnosis of SS includes the presentation of 3 or more of the above with no other logical reason to explain such presentation (i.e. other than drug-drug interaction). This clinical scenario is usually mild and will resolve when the drugs have been stopped. However, in some cases it can be fatal. Therefore, as a clinician, a sound understanding of SS presentation is key.
I hope this blog edition has been of use to you in explaining the factors that you need to consider when switching antidepressant medication. I also hope that the reference I provide offers more information and understanding. The summary of SS has been of great use to me in aiding my understanding the clinical manifestation and I hope the same goes for you.
Please get in touch with me if you need any help with your studies or applications. That’s why I set my company up, to help people succeed in often-times quite complex areas of medicine / healthcare.