Annual global spending on prescription drugs will rise 25% by 2016 to $1.2 trillion, as surging growth in emerging markets eclipses weak gains in developed markets like the United States, according to healthcare information provider IMS Health.

However, the expected spending growth, averaging 3 to 6% a year over the next five years, pales with the 6.1% annual growth seen during the previous half-decade.

That's largely because of recent or looming patent expirations on top-selling branded medicines such as Bristol-Myers Squibb's blood clot preventer Plavix, Eli Lilly's Cymbalta depression treatment and Merck & Co's Singulair asthma pill, according to the IMS report.

Cheaper generic forms of the blockbuster medicines will then flood the marketplace.

All told, patent expirations will wipe out $106 billion of sales from branded drugs over next five years, with the heaviest toll coming this year and in 2013, IMS said in its report forecasting trends over the next five years.

The worst "patent cliff" in history, which erased $72 billion worth of branded-drug sales between 2007 and 2011, will then have largely run its course.

"The developed markets will then come back from their lowest point to a modest level of annual growth, in the low-single digits percentage range," said Michael Kleinrock, director of Research Development for IMS.

"They're not charging back to the high single-digit or double-digit growth you may have seen in the early 2000s, but they are returning to positive growth," he said.

Worldwide sales of generics, a mainstay in poorer countries, will almost double to between $400 billion and $430 billion by 2016, driving overall spending growth on pharmaceuticals, IMS said.

By contrast, sales of branded patent-protected medicines will be little changed, growing only 3 to 8% to between $615 billion and $645 billion by 2016. That translates into possible annual growth of less than 1%.

In the United States, the world's most lucrative market for branded medicines, annual drug spending will likely grow 1 to 4% over the next five years, from average annual growth of 3.4% during the previous half-decade.

Developed markets, which also include Europe, Japan and South Korea, represented almost three-quarters of global drug spending in 2006. They will account for only 57% by 2016, IMS said, as emerging markets strengthen.

IMS expects annual spending in emerging markets to grow 12 to 15% from 2012 to 2016. While eclipsing growth forecast for developed markets, that represents a slowdown from average annual growth of 16.3% in the previous five years.

"The key thing we will see over the next five years is a rebound in pharmaceutical sales growth, but not from the traditional sources," said Kleinrock. "In the past, sales growth came from developed markets, branded medicines and blockbuster drugs."

"In the next five years we will see the maturation, the evolution, of emerging markets -- which are heavily generic and driven by volumes primarily rising from very low-income people that have become more affluent or are otherwise getting better access to medical care," Kleinrock said.

The most important emerging markets include China, Brazil, Russia and India. But even their sales growth rates, although sizzling, are beginning to wane as the nations progress into mature markets, Kleinrock said.

For instance, IMS said sales of prescription drugs in China grew by an annual average of almost 24% between 2007 and 2011, but are expected to slow to 15 to 18% annual growth over the next five years.

A bright spot in the IMS report is a prediction that 160 to 185 new molecular entities, meaning medicines with new chemical structures, will be approved by 2016. That compares with 142 approved in the previous five year period.

Approvals of more orphan drugs -- those for relatively rare diseases -- will account for some of the improved track record, along with more-advanced drug discovery techniques and other factors.