Losing a megablockbuster to generic competition can be painful for a drugmaker. Just ask Pfizer (NYSE:PFE) that lost Lipitor or Bristol-Myers Squibb (NYSE:BMY) that lost Plavix. Revenue was down 10% and 17% in 2012, respectively.

But at least they have another potential blockbuster coming up from behind to deaden the blow.

Merck's (NYSE:MRK) investors? They'll have to wait.

Fourth-quarter revenue at Merck was down 4.5% as the market was flooded with copycats of the company's asthma drug Singulair. Merck's Janunvia diabetes drug franchise and its HPV vaccine Gardasil helped close the $1 billion gap, but it wasn't enough.

Merck's osteoporosis drug, odanacatib, was supposed to help get things back on track. Last year, a phase 3 trial was ended early because it was clear that the drug was working, but the company revealed today that it won't seek FDA approval for odanacatib this year as expected. The plan is to wait for an extension trial to produce longer-term data before applying next year.

In theory, the added data should make it easier to get past the FDA. And having the additional info on the label should make it easier for Merck to compete with the current osteoporosis drugs. Doctors have a lot of experience with older medications like GlaxoSmithKline and Roche's Boniva and Merck's Fosamax, which is already available as a generic, so more data can't hurt.

The delay is just another in a series of bad news for Merck. Cholesterol drug Tredaptive also had the potential to become a blockbuster, but an outcomes study revealed in December that the drug didn't decrease cardiovascular events -- heart attacks, strokes, and the like -- when added to a statin, such as Pfizer's Lipitor or AstraZeneca's Crestor.

Merck will eventually turn things around, but it isn't going to happen this year. The company is guiding for adjusted earnings of $3.60 to $3.70, well below the $3.82 that it posted in 2012. If you're going to own Merck, you'll need to do it for the long term, collecting the substantial dividend while you wait for better times.