Sanofi performed strongly in China, Brazil and Russia - crucial areas for international drugmakers as sales in their home markets decline due to patent expiries and government cuts in healthcare spending.

Its sales to emerging markets in the quarter rose 9.9 percent at constant exchange rates, in sharp contrast to an anemic 2 percent gain at GSK and just 1 percent at AstraZeneca.

The booming middle classes of Asia and Latin America are expected to offer robust growth for makers of prescription drugs in the years ahead, but selling medicines into countries such as China, Russia, Brazil and Turkey can be tough.

Sanofi's rivals said they were hurt by instability in the Middle East, price cuts in Russia and Turkey, and early generic competition in Brazil.

"(Sanofi's) strong performance in emerging markets in particular will please, as will reiteration of guidance," Deutsche Bank analysts said in a note to investors.

Sanofi shares, which have risen around 8 percent in the last year, were the second-best performers on the CAC40 index at 0815 GMT, trading up 2.9 percent at 58.41 euros, while the index was down 0.1 percent.

RETURN TO GROWTH

The Paris-based company confirmed that earnings could decline between 12 and 15 percent this year as top-selling drugs previously protected by patents, including blood thinner Plavix, are hit by competition from cheap copies.

But it expects to return to growth in subsequent years thanks to emerging markets, diabetes, vaccines, animal health, Genzyme's biotech drugs and new products such as experimental multiple sclerosis drug Lemtrada.

"Although, as expected, Plavix will lose exclusivity in May in the U.S., the strong underlying performance of the business is consistent with our medium-term growth outlook," Chief Executive Chris Viehbacher said in a statement on Friday.

Sanofi posted a 12.5 percent rise in first-quarter business net income to 2.44 billion euros ($3.23 billion), driven by a strong performance in emerging markets, biotech unit Genzyme, and diabetes drug Lantus. Consumer healthcare products and cost savings also helped drive earnings higher.

The result beat the average estimate in a Reuters analyst poll of 2.217 billion euros.

Sanofi said group sales rose 9.4 percent to 8.51 billion euros, thanks to a weaker euro, though they slipped 0.6 percent at constant exchange rates and adjusting for the consolidation of Genzyme.

Sales at Genzyme rose 13.7 percent to 400 million euros after it resumed delivering rare disease drug Fabrazyme from a newly approved plant in Massachusetts. Genzyme had been forced to ration the drug in 2009 due to production problems that also led to shortages of another rare disease drug, Cerezyme.

"Organic growth is close to break even, which confirms that it will be positive in the full year," said Natixis analyst Philippe Lanone.

BOLT-ON ACQUISITIONS

Viehbacher told reporters on a conference call that Sanofi did not "particularly need to do any" mergers or takeovers, but that it would look at bolt-on acquisitions to bolster its consumer healthcare and emerging markets business.

He declined to comment on possible interest in Amylin Pharmaceuticals or Human Genome Sciences, however.

U.S. biotech Human Genome, which rebuffed an unsolicited $2.6 billion takeover bid by GlaxoSmithKline, said on Tuesday it was reviewing strategic options that included a sale of the company.

Amylin started reaching out to potential buyers earlier this month, according to sources familiar with the situation.

($1 = 0.7559 euros)

(Additional reporting by Ben Hirschler and Noelle Mennella; Editing by James Regan and Andrew Callus)

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