Would have a better chance suing on invalidity of the misinfo charge .... Ivermectin works and is authorized by the FDA and make them prove misinfo.
There used to be a concept called “therapeutic privilege”
As you say, Ivermectin has a license (to treat worms), but once licensed, any prescriber can use it for any purpose.
The concept of therapeutic privilege is, or was, if I have given it to patients for disease X and I believe I have had good results, that’s enough evidence to keep me safe.
This is no longer the case - and not just, or not even mainly, about COVID.
It’s a big change, the new standard is “evidence”, which would be fine except there is no evidence for most things, and in March 2020 there was NO EVIDENCE, of any kind, about COVID treatment.
So, the “evidence” forces have decided that the opinion of experts is evidence of a sort - and that has created a big problem.
Full disclosure: I don’t believe ivermectin has any useful activity for COVID treatment, but my opinion alone is not a sufficient basis to regulate what other prescribers do.