I wouldn't test the drug. But the hypothetical doesn't sit well with me. In clinical trials drugs are tested on animals until something shows that the benefits outweigh the risks. You would either have a good idea that the 10,000 people would likely get better from the drug you were testing, or you would have no proof that the drug will benefit them at all and therefore couldn't ever guarantee that after 10,000 people the drug would be perfect.
Anyway, wouldn't test it in this hypothetical because you are basically asking if you would kill some people to save unknown other hypothetical lives later. Can't really be justified.