Deutsche Apotheker Verlag (DAV) is offering access to its most important textbooks until June 30, 2020(link).

You can find an overview of the titles here(PDF).

The textbooks are only accessible online, i.e. they cannot be downloaded. They are not listed in the catalog. They can be opened by clicking on the green button "Open textbook".
Access is possible within the HSZG campus network. Only for members of the HSZG is access also possible from outside the campus network via a VPN connection with the university.