This is a table of clinical trial approval rates at each stage:
Stage of Development Probability of Approval
- Phase 1 9%
- Phase 2 15%
- Phase 3 44%
- Submission 80%
Hence only ~6 make it to the application for approval to the FDA (this is US data, but its broadly similar over here)
However I think its worth looking at the success rate of those trials;
Clinical Trial Phase Probability of Success
- Phase 1 63%
- Phase 2 33%
- Phase 3 55%
- Approval 80%
But loads of drugs have some biological effect, but can't be used because they kill you as well. (but these drugs have been tested on humans, so they are not arsenic or rat-poison etc)
Many of these problems are that the drug might work on hypertension but it also toxic, hence if some company can develop novel delivery methods to for example selectively deliver a drug to the liver or the heart, and avoid the kidneys, then loads of those "non-approvals" but "successful phase-1" drugs get another chance.
ie, the pharmas would pay a fortune, because they have cupboards full of these fucking drugs which they can't use because of the above reasons.
One technique is construct a drug with two parts, the one with the biological active site, and then make that bound to a big fat sweaty molecule that is known to be excreted by the kidneys, but not effects the target organ.
Then, badda-bing, let the cash roll in.