By Ben Hirschler, European Pharmaceuticals Correspondent

LONDON (Reuters) - As sales of big-brand medicines in the United States and Europe falter, Western drug companies have new targets in their sights -- the emerging wealthy middle classes of China, India and Russia.

And such a drive into new areas of double-digit revenue growth could trigger a wave of restructuring and unconventional deals, analysts predict.

GlaxoSmithKline (GSK.L: Quote, Profile, Research) chief executive-designate Andrew Witty last week made emerging markets a top priority by poaching Eli Lilly (LLY.N: Quote, Profile, Research) manager Abbas Hussain to head a new region focused on such countries in a high-level reshuffle.

The world's second-biggest drugmaker reckons emerging markets account for nearly 25 percent of drug sales growth and will grow three times faster than western countries. Glaxo is not alone.

"All the major pharma companies are taking a fresh look at their strategies to really take advantage of the emergence of these major new markets," Murray Aitken, senior analyst at healthcare information group IMS Health (RX.N: Quote, Profile, Research), told Reuters.

"The slowdown that we're seeing in the developed part of the world is helping to accelerate these reviews."

Increased generic competition at home and failing new drug pipelines mean the sector's traditional defensive reputation is under siege.

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