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Pimavanserin: Selective 5-HT2A antagonist for serotonin toxicity?

pimavanserin serotonin toxicity serotonin syndrome 5-ht2a 5-ht3 5-ht1a serotonin antagonist

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#1 BioInfinite

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Posted 21 May 2016 - 04:20 AM

Pimavanserin is a newly released non-dopaminergic anti-psychotic highly selective for 5-HT2A. 


In theory, would such properties treat or exacerbate serotonin toxicity?


My theory is that if you block certain serotonin receptors, there will be more serotonin available to bind to other serotonin receptors, like for example 5-HT1A pre- or post-synaptic, or 5-HT3 receptors.


At a high dose, pimavanserin causes nausea and vomiting, something that blocking 5-HT3 receptors antagonises. I expect there becomes more serotonin to activate 5-HT3 which is anxiogenic and induces nausea/vomiting.


Also, selective 5-HT3 antagonists such as Ondansetron have been proven to worsen or help to cause serotonin syndrome, presumably because blockade allows free serotonin to activate other receptors such as 5-HT2A.


Is this accurate or am I way off here? 

#2 Finn

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Posted 28 May 2016 - 05:28 AM

Different serotonin receptors are more responsible for different bodily functions. 5-HT2A seems to be the receptor most responsible for the most fatal reactions, it is much preferable to vomit (5-HT3 overstimulation) for example than it is to experience extreme hyperthermia. Rats given 5-HT2A antagonists didn't die of serotonin syndrome when give MAOI-A/tryptophan combo, others died.


Potent serotonin (5-HT)(2A) receptor antagonists completely prevent the development of hyperthermia in an animal model of the 5-HT syndrome.





Apparently at least in child patients on chemotherapy and serotonergic antidepressants, when given 5-HT3 antagonists to prevent vomiting, this has left more serotonin for 5-HT2A and thus induced serotonin syndrome.


But to avoid worst symptoms of serotonin syndrome it is much better to overstimulate other receptors than 5-HT2A, thus 5-HT2A antagonists can be used to treat serotonin syndrome.

Edited by Finn, 28 May 2016 - 06:22 AM.

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#3 Heyguy

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Posted 22 March 2018 - 01:22 PM


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#4 BioInfinite

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Posted 25 May 2024 - 05:03 AM

Ok so it's been quite a few years since I made this post. I've been on antipsychotics for a decade now to treat serotonin sensitivity following toxicity. I want to try it as an adjunct to my anti-psychotics (quetiapine and cariprazine) with a goal to reduce both as much as possible. 


I'm considering ordering some pimavanserin tartrate from a Chinese chemical supplier with a current COA showing a 99.8% purity. I want to take as many precautions as possible, so I would be starting at a very low dose, and dissolving in liquid to measure.


I would try and get it prescribed but it's incredibly expensive in the US ($5000 for a bottle), and it's unavailable where I live. 


Research has shown synergistic effects with other antipsychotics such as risperidone, and has been combined with quetiapine without issues. I've thoroughly studied prescribing guidelines, interactions and contraindications, half life, research articles etc.


I'm open to any suggestions. I would have it tested independently but I don't know of a lab or how much it would cost.


I know there are a few people on here that had a similar experience to me regarding serotonin sensitivity following toxicity, so I'll happily report back if I do decide to go ahead. 


Does anyone have experience with Pimavanserin? 


And any experience or tips for ordering from Chinese companies?

Also tagged with one or more of these keywords: pimavanserin, serotonin toxicity, serotonin syndrome, 5-ht2a, 5-ht3, 5-ht1a, serotonin antagonist

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