It's nice to have a drug on the market, but it's even better to not have any competitors. So nice, in fact, that the launch of a generic version of sanofi-aventis' (NYSE: SNY) Lovenox led Momenta Pharmaceuticals (Nasdaq: MNTA) to its first profitable quarter ever.

Momenta's partner, Novartis (NYSE: NVS), had already spilled the beans about the successful quarter of $292 million in sales of the generic product, but investors had to wait until Momenta reported earnings to see the impact on the bottom line.

After all the expenses for making and selling the drug were taken care of, Momenta's share of the profits came out to $44 million. But -- and this is a big but -- Momenta was required to repay $35 million of prelaunch costs that Novartis fronted, which came out of the profits in the third quarter. Without those costs, which are now paid in full, Momenta would have brought in $79 million from the generic drug.

If you assume that $35 million goes right to the earnings line and back out a one-time $5 million milestone payment, Momenta could have earned a profit of about $1.35 per share. The third-quarter sales were higher due to stocking by pharmacies, but if you assume Novartis can penetrate the market further and use that as a run rate, you get $5.40 per share in annual earnings. Subtract out 30% since Momenta will eventually have to start paying taxes, and you're still at $3.78, or a P/E under 5.

Sounds cheap, no? There's just one problem. Those earnings are based solely on the fact that there aren't any other generic competitors, which allows Novartis to price the drug at close to the price of branded Lovenox. If the Food and Drug Administration approves a pending application from Teva Pharmaceutical (Nasdaq: TEVA) and another from Amphastar Pharmaceuticals, which is partnered with Watson Pharmaceuticals (NYSE: WPI), Novartis will have to drop the price, and Momenta's share changes from a profit share to a royalty.

Without any indication of when or if those applications will be approved, investors don't have much other choice than to price in the possibility that Momenta's momentum will be stopped and enjoy the insane profits while they last.

At the other end of the spectrum, Morgan Housel points to the attack of the 50 P/E stocks.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Momenta Pharmaceuticals is a Motley Fool Rule Breakers recommendation. Novartis is a Motley Fool Global Gains choice. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Fool owns shares of Teva and has a disclosure policy.