Cost cuts helped drugmakers shore up profits in the third quarter, but concerns over sustainable revenue growth continues to worry investors.

Merck & Co earnings easily beat Wall Street expectations on Thursday, while rivals Novartis and Bristol-Myers Squibb Co posted profits largely in line with projections.

But the drug companies posted modest increases in sales and face patent expirations to their biggest products in the next few years, a problem endemic throughout the pharmaceutical industry.

I'd really like to start seeing more solid top line growth -- they've all been rather tepid, said Eldene Doyle, an equities analyst with Optique Capital Management. That combined with the patent cliff is really weighing on everybody's minds.

Shares of Merck were down 1.3 percent in morning trading in New York after falling as much as 4.3 percent, while Bristol fell 1.2 percent. Swiss-based Novartis slipped 0.1 percent.

Shares of Schering-Plough Corp , which has agreed to be bought by Merck, fell 0.6 percent after posting profit that met expectations.

Earlier this week, cost cuts helped both Pfizer , the world's biggest drugmaker, and Eli Lilly top forecasts -- though their results also failed to excited investors.

One thing I'm seeing is continued cost cutting really strengthening the bottom line, Morningstar analyst Damien Conover said. This is a theme that is going to be playing itself out for several more quarters to come.

Sales of Merck's diabetes and HIV treatments combined with cost controls helped drive the better-than-expected quarterly profit, although overall sales rose just 2 percent to $6.05 billion.

Merck reported net income of $3.42 billion, or $1.61 per share. That compared with $1.09 billion, or 51 cents per share, in the year-earlier period.

Excluding special items, Merck earned 90 cents per share. Analysts on average expected 82 cents per share, according to Thomson Reuters I/B/E/S.

The New Jersey-based drugmaker forecast full-year earnings of $3.20 to $3.30 per share, excluding items, raising the low end of its earlier forecast from $3.15.

Leerink Swann analyst Seamus Fernandez said sharp initial declines in Merck shares may have been spurred by concerns that the company -- like other drugmakers that beat third-quarter profit forecasts -- did not raise the upper end of its full-year forecast.

They just kind of tightened the range, Fernandez said. He said Merck shares may have also been hurt by concerns that Abbott Laboratories' Niaspan might prevail against Vytorin and Zetia in a cholesterol study that will be presented at a major medical meeting in November.

Novartis said sales would grow faster than expected this year, even without a shot in the arm of up to $700 million from its H1N1 swine flu pandemic vaccine.

Third-quarter net profit nudged up 1 percent to $2.1 billion, in line with forecasts. Sales rose 3 percent to $11.09 billion.

Joe Jimenez, chief executive of Novartis' drugs unit, told Reuters its productivity initiative for the year was going well and there is room for further cost savings.

That is helping significantly to raise our margins at a time when we are investing heavily in our new launches, Jimenez said.

Novartis now expects group sales to grow at a high single-digit rate, even excluding H1N1 pandemic flu vaccine sales, and sees drugs sales growth at a double-digit rate.

At Bristol-Myers, revenue trailed analyst estimates, although earnings from continuing operations jumped 64 percent.

Excluding items, Bristol posted earnings of 52 cents per share. Analysts on average expected 51 cents per share, according to Thomson Reuters I/B/E/S.

Revenue rose 4 percent to $5.49 billion, slightly below the $5.52 billion expected by analysts.

Bristol, which is cutting jobs as part of an efficiency drive, reported an 8 percent decline in marketing, selling and administrative expense, to $1.1 billion.

(Additional reporting by Ransdell Pierson in New York and Sam Cage in Zurich, editing by Dave Zimmerman)