GlaxoSmithKline will this week inform U.S. staff of hundreds of job cuts in its biggest market as the drugmaker starts implementing a major cost-saving programme, sources familiar with the matter said on Sunday. Britain's top drugmaker announced at third-quarter results on Oct. 22 that the new restructuring scheme would save 1 billion pounds in annual costs over three years, but it has yet to tell employees where the axe will fall.