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Re: ritanserin, pimavanserin, and lumateperone SLS

Posted by undopaminergic on September 12, 2021, at 13:54:19

In reply to ritanserin, pimavanserin, and lumateperone undopaminergic, posted by SLS on September 12, 2021, at 12:52:04

> Hi, UD.


> > > Ritanserin is probably the most selective 5-HT2 antagonist in the world. When I looked in on it a bunch of years ago, it was reported to be virtually devoid of side effects. It is a drug without an indication. It has no other purpose that I recall other than being an antidepressant augmenter. By itself, it is inert.
> > >
> > >
> > > - Scott
> > But ritanserin is not clinically available as far as I know.
> >
> > -undopaminergic
> Exactly.

Right. But my question was about what is the best serotonin 5-HT2C antagonist that is clinically available.

I have previously encountered ritanserin, while reading neuroscientific research. It is very useful in researching the serotonergic system.

I would use it if I could acquire it readily. As it is now, I need something a doctor can prescribe.

> Ritanserin is a great drug without an indication. What clinical value does this drug have as monotherapy? None.

I'm not convinced of that, especially not if it is all that you say it is (ie. an *inverse* agonist). I would expect dose-dependent effects, including, possibly, a stimulant (inverse of apathy) effect.

> However it's possible that ritanserin would be a miracle augmenter of antidepressant treatment.

What I need it for is to block the apathy arising from the use of clomipramine or sertraline.

> Ritanserin acts as a "selective" ligand of:
> 1. 5-HT2a receptors (Ki = 0.45 nM)
> 2. 5-HT2c receptors (Ki = 0.71 nM).
> Ritanserin is labeled either a "selective" or "non-selective", depending on the authors of the available medical literature. At these receptors, ritanserin functions as an INVERSE AGONIST. An inverse agonist really acts as a super-antagonist. If a receptor is antagonized (blocked), it prevents the neuron from being stimulated in a neutral fashion. For example, let's say that the baseline level of neuron excitability in the absence of pharmacological intervention neuronal = 100 units. A pure antagonist might bring the excitability of the the neuron down = 0 units. Now, an "inverse agonist", when bound to the same receptor, will move the level of excitability to *below* the baseline = negative (-) 100. The inverse agonist actually suppresses the excitability of a neuron *below* its baseline. In a way, an inverse agonist actually causes a cell to do exactly the *opposite* of what an agonist does.

Yes. I did not know it was an inverse agonist.

> Although sometimes considered to be non-selective for all of the three subtypes of 5-HT2 receptors, Ritanserin really isn't. It does not bind to the 5-HT2b receptor subtype.

Wikipedia says it binds to other receptors too, including 5-HT2B, but does not report affinity values:

> There are three drugs other drugs that are supposed to be potent 5-HTa/c antagonists:
> 1. Pimavanserin
> 2. Roluperidone
> 3. Lumateperone.
> Unlike ritanserin, these drugs have other pharmacological properties. They aren't "clean". Of these, both pimavanserin and lumateperone have been approved by the FDA ...

Alas, they aren't approved in my locale (yet).

> ... for the treatment of hallucinations and delusions associated with Parkinson's disease. In addition, they seems to be effective in treating schizophrenia to treat both positive AND negative symptoms. These drugs are currently under investigation for treating Bipolar Depression.
> - Scott

You don't mention asenapine (Sycrest, Saphris). This is currently my main candidate.





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