The drug was marketed in 1997, and 14 years of post marketing experience with Propecia has shown that the drug is NOT safe. As I said, several independent studies have proven that the drug does a lot more than just reducing the level of DHT, and increasing the total testosterone- and estrogen level as Merck claims.
RU58841 was abandoned for several reasons. The most obvious one is; drug trials costs a lot of money, and apparently - there is no reason to use a lot of money to bring a product to the market, which 1) isn't more effective than Propecia in the short term, 2) is as inconvenient as Rogaine to use, and 3) is supposedly safe, and only 2% of the users experience any side effects - which will subside when you quit the treatment. Prostrakan abandoned RU58841 many years ago, but other people have been working on it too. Aventis Pharma filed a patent on some new solutions that addresses the issues with RU58841, in November 2010.
Another thing, local treatment is always safer than systemic treatment.