Merck (NYSE:MRK) and Schering-Plough (NYSE:SGP) reported earnings as separate companies for likely the last time yesterday, but that doesn't mean investors and Foolish analysts need to treat them separately. Here's what the companies might have looked like if they were already combined.

Combined sales would have been essentially flat, excluding the joint ventures Merck has with Johnson & Johnson (NYSE:JNJ), sanofi-aventis (NYSE:SNY), and AstraZeneca, but including sales of its joint venture with Schering-Plough. Technically, sales were down 0.4%, but we're getting close to rounding error at that level.

The way you get to the flat sales isn't pretty, though. Look at the top 10 franchises:

Drug

Sales (in Millions)

Year-Over-Year Increase/(Decrease)

Singulair

$1,085

5%

Zetia and Vytorin

$1,028

(7%)

Cozaar and Hyzaar

$861

(3%)

Januvia and Janumet

$664

39%

Remicade

$608

8%

Gardasil

$311*

(22%)

Nasonex

$266

3%

Temodar

$278

2%

Fosamax

$276

(22%)

PegIntron

$198

(16%)

Source: Company releases.
*Excludes joint venture sales with Sanofi.

Diabetes drugs Januvia and Janumet are carrying the companies. They registered undeniably impressive growth, but I'm not sure how long Merck can keep that up. Bristol-Myers Squibb (NYSE:BMY) and AstraZeneca recently launched a similar drug, Onglyza, and Amylin Pharmaceuticals (NASDAQ:AMLN) and Eli Lilly (NYSE:LLY) have a once-weekly diabetes drug under review with the FDA.

International growth in sales of Remicade is also making a major contribution, but it's not entirely clear whether the combined company will be able to hold onto its ex-U.S. marketing rights for the drug. Johnson & Johnson wants them back because of Schering's change in ownership.

The bottom-line earnings are a little harder to combine, but it doesn't really matter at this point. The basis for combining the companies was synergistic cost reductions, which won't show up while the companies are still separate.

How much those cost savings will come to fruition remains to be seen, but one thing is clear: The new Merck will need a boost from its pipeline to get growing again. Resting on its current blockbusters isn't going to cut it.

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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.