Merck (NYSE:MRK) and Schering-Plough (NYSE:SGP) are up today on "better than expected" earnings, but the bride and groom don't look all that great heading into the wedding.

Just take a look at the drugs on pace to become blockbusters this year:

Drug

Current Seller

Sales (in millions)

Year-Over-Year Increase (decrease)

Singulair

Merck

$1,300

16%

Zetia and Vytorin

Merck and Schering

$1,000

(10%)

Cozaar and Hyzaar

Merck

$906

(4%)

Remicade

Schering

$565

2%

Januvia

Merck

$462

38%

Nasonex

Schering

$321

3%

Gardasil

Merck

$268*

(18%)

Temodar

Schering

$256

2%

*Excludes sales from joint venture with sanofi-aventis (NYSE:SNY), which Merck doesn't break out.

With the exception of Januvia, nothing stands out as stellar. The increase in sales of Singulair is impressive, especially since growth was stunted last year as doctors worried about reports of increased suicide risk, but the U.S. patent expires in 2012, so there isn't too much more room to run.

Sales growth of Remicade would have been 19% if the stronger dollar hadn't smacked the year-over-year comparison down, but Merck and Schering aren't guaranteed to be able to sell the drug once they wed. Partner Johnson & Johnson (NYSE:JNJ) wants to take back the rights to it and up-and-comer Simponi under a change-in-control clause and has taken them to arbitration.

In total, Merck's sales were up 3%, excluding the negative impact of currency exchanges; the smaller Schering saw sales increase 4%, excluding currency changes. That's nothing to write home about, even if it was better than expected.

I liked the Merck and Schering deal more than the Pfizer (NYSE:PFE) and Wyeth (NYSE:WYE) merger, but investors should still be very cautious here. Until Schering's well-stocked pipeline works its way through the approval pathway, revenue could be stagnant for a while.

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