as I see some differences in such data from website to another specially the solubility and pKa
You can check the following links to search for the chemical and physical properties of pharmaceuticals:
-https://pubchem.ncbi.nlm.nih.gov/search/
-https://toxnet.nlm.nih.gov/
-https://www.drugbank.ca/
There might be many more links, but I get required info. from above links.
Actually these websites are already my references they are good but some times I find some differences between them, that why I ask for a written reference
I don't think there can be a better reference then these, as these are from NIH. Other options are to go through US-FDA or EMA website, download the documents for that particular drug from there, and then get the desired information from there.
-https://www.accessdata.fda.gov/scripts/cder/daf/
-https://www.ema.europa.eu/en/medicines
If these still don't serve your purpose, go to pharmacy/chemistry department of your university, and ask them about some catalogs/encyclopedias which compile such information as hard copies.
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