It took long enough, but the wait was worth it.

Motley Fool Rule Breakers recommended Momenta Pharmaceuticals (Nasdaq: MNTA) to subscribers back in the September 2006 issue. Nearly four years later, the investment paid off with shares up over 70% today thanks to a Food and Drug Administration approval of its generic version of sanofi-aventis' (NYSE: SNY) Lovenox.

Normally the approval of a generic drug wouldn't trigger that kind of response, but this is no ordinary generic. Sanofi sold 1.8 billion Euros worth of Lovenox in the U.S. last year, which translates into about $2.3 billion at today's exchange rate.

More importantly, Lovenox is a fairly hard drug to make. That's the reason the FDA took so darn long to approve the drug, but the complexity provides some protection from competition. Both Teva Pharmaceuticals (Nasdaq: TEVA) and Amphastar Pharmaceuticals have applications pending with the FDA, but so far, neither has announced an approval.

Novartis (NYSE: NVS), Momenta's commercialization partner, plans to launch the drug soon. You can expect that with no other generic competition, the price will be fairly close to the price of brand-name Lovenox.

How long the competition-free period remains is very important because it'll affect not only the price of the generic drug, but also Momenta's share of the revenue. If Momenta and Novartis' product is the only generic on the market, Momenta gets a profit share of between 40% and 50%. If other competitors make it to market, Momenta only gets a royalty in the high single-digit to low double-digit.

Looking ahead for Momenta, its first FDA approval is an endorsement of the company's technology of characterizing and copying complex molecules. In addition to generic Lovenox and helping the FDA sort out Baxter's (NYSE: BAX) heparin contamination issue, the company is working on a generic version of Teva's Copaxone, another highly complex drug.

Hopefully investors won't have to wait nearly as long for Momenta's second approval.

You can read the original recommendation of Momenta and see the analysts' current opinion by grabbing a 30-day trial subscription to the Motley Fool Rule Breakers newsletter. 

Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Novartis is a Motley Fool Global Gains choice. The Fool has a disclosure policy.