Shire's share price chart still looks like a worryingly erratic heartbeat. The specialist pharmaceuticals company has seen its stock drop 22 per cent over the past six months as market concerns intensify about Vyvanse, its lead drug. Vyvanse is a next-generation treatment for attention deficit hyperactivity disorder, whose yearly sales are forecast to peak at $1bn (£506m). It replaces Adderall XR, Shire's best-selling treatment for ADHD whose patent expires in 2009. But the market is concerned people are not moving quickly to the new drug. If enough patients are not switched on to Vyvanse before the generic version of Adderall arrives the revenues generated by Adderall will drop sharply. Shire is managing to switch over the equivalent of less than 1 per cent of market share each month - Adderall has a 30 per cent market share. The good news is this month the US Food and Drug Administration will decide whether to approve Vyvanse in adults, who represent 40 per cent of the ADHD market. Collins Stewart forecasts full-year sales of $2.8bn and profits of $722m for 2007. The shares trade on a price/earnings multiple of 19.2 times, a premium to rivals. Salamander Davoudi