* Sanofi, Roche await approval for eczema and MS drugs

* GSK faces potential generic competition to Advair

* U.S. FDA due to give verdicts next week

By Ben Hirschler

LONDON, March 23 (Reuters) - Three of Europe's top drugmakers face critical verdicts from U.S. regulators next week, with Sanofi and Roche likely to win approvals for two new products, while GlaxoSmithKline braces for a potential generic rival.

Given earlier impressive clinical trial results, investors expect the Food and Drug Administration (FDA) to clear both Roche's multiple sclerosis (MS) treatment Ocrevus and Sanofi's new eczema drug Dupixent.

The two FDA decisions, due by March 28 and 29 respectively, mark important landmarks for both firms, since Dupixent and Ocrevus are expected to be the biggest new drug launches from the global pharmaceuticals industry in 2017.

Dupixent, developed with Regeneron Pharmaceuticals, is forecast to sell $4.2 billion annually by 2022, with Ocrevus seen hitting $4 billion by that time, according to the consensus of analysts' estimates compiled by Thomson Reuters.

Sanofi's research head says Dupixent marks a new era of successful innovation for the French company, although the product is tied up in a patent dispute with Amgen.

The remarkable success of Ocrevus against two types of MS, meanwhile, will help Roche diversify beyond cancer. The drug has beaten rivals in fighting relapsing remitting MS and could become the only approved drug for primary progressive MS.

ADVAIR CHALLENGE FOR GSK

The picture is a lot less certain for Britain's GSK as it faces the threat of cut-price competition from Mylan, which hopes to secure approval for the first substitutable generic copy of GSK's top-selling Advair lung drug by March 28.

Mylan believes it has done everything required to win FDA approval but its version of Advair would be the first complex inhaled combination generic product to be approved by the U.S. agency, so nothing is guaranteed.

That complexity has led some analysts to question whether Mylan will succeed at its first attempt to gain approval, potentially delaying the arrival of generics and shielding GSK's profits from immediate attack.

A second generic version of Advair from Hikma Pharmaceuticals and Vectura is also awaiting an FDA approval decision by May 10.

Dealing with the threat of competition to Advair, which has generated more than $1 billion in annual sales since 2001, is the first big challenge facing GSK's new chief executive, Emma Walmsley, who takes over at the end of this month.

GSK has told the market that core earnings per share, in constant currencies, will be flat to slightly lower in 2017, if substitutable Advair generics arrive in the United States by mid-year. If they don't launch, EPS should rise between 5 and 7 percent.

(Editing by Greg Mahlich)