Does anyone know what the rate of success must be for an FDA approved clinical trial.

Sadly, I do not.

Check this out: http://www.fda.gov/ScienceResearch/SpecialTopics/RunningClinicalTrials/default.htm

Might be a link or two there that can help somewhat. I would have to guess that there isn’t a statistical rate that must be achieved for some things. For example, there is currently a narcotic on the market for the treatment of fibromyalgia symptoms. While the drug poses mild adverse affects, it doesn’t generally worsen symptoms and in some cases helps them. As it poses no significant risk of harm and in some cases helps, it seems to be appropriate for market. I wish I could be of more help. That link includes a ‘contact the FDA’ link. Also, try contacting a local university and getting a pharmacology/genetics/biochemistry grad student on the phone.