Andrew Witty is in good company as he gears up to take charge of the world's second largest pharmaceutical group next spring. His recent nomination to head GlaxoSmithKline marks the seventh example in the past two years of a change in chief executive among the world's 10 leading drug-makers.

While each of the handovers has unique aspects, the characteristics of the new generation of pharma leaders - and the way in which they were selected - reveal some common patterns that highlight evolutions and challenges in a sector going through rapid and painful transition.