Shouldn't be any TM issues, no. Viagra's trademarked, the brand name, but you can't trademark the generic name of a chemical (Sildenafil Citrate is the chemical that makes up Viagra)Perhaps the patent is invalid but there is still a TM issue no ?
Anyway, this looks like a domain with only one obvious end user, that must have lawyers on a retainer willing to handle cybersquatting issues...

