thanks for posting this interesting technical question on RG. For some potentially helpful information about the solubility of atorvastatin in different solvents please have a look at the following data sheet:
Atorvastatin (calcium salt hydrate)
https://cdn.caymanchem.com/cdn/insert/10493.pdf
The main problem here seems to be the low solubility of the compound in water and aqueous buffers.
In this context, please also check the following research article which has been published Open Access:
Solubility and Bioavailability Enhancement of Poorly Aqueous Soluble Atorvastatin: In Vitro, Ex Vivo, and In Vivo Studies
Article Solubility and Bioavailability Enhancement of Poorly Aqueous...
This paper is freely available as public full text right here on RG and can be downloaded as pdf file. I hope this helps answering your question. Good luck with your work and please stay safe and healthy! With best wishes, Frank Edelmann