Broker Panmure Gordon downgraded GlaxoSmithKline after its heart drug Darapaldib, 'the great white hope in the pipeline', failed to reach its primary end-point in a late-stage trial.Analyst Savvas Neophytou trimmed his forecasts, mainly assuming a £150m writedown in the fourth quarter even though a second Phase III trial is still ongoing with results expected in the first half of 2014. "Even if that [second] trial was successful, we believe it will be difficult to gain market registration on one trial alone," he said, with the market having been forecasting Darapaldib launch in 2015. He added that should the product ever reach the market he still believes it offers "vast potential".But Neophytou noted this was the second big disappointment in the year, following similarly negative outcome from the MAGEA3 cancer trial in September."We note that further data is expected from a number of pipeline assets in Q4, but to us darapladib had been the great white hope in the pipeline, a product that could have reached $10bn in revenues if successful."The analyst cut his 2013 earnings forecasts from 116.45p to 114.06p and said the valuation was "not undemanding", trading at a premium to the sector.Acknowledging that the company has been through the majority of its patent expiries and big liability settlements, boasts a strong balance sheet, has very little M&A risk and a secure dividend, Panmure downgraded from 'buy' to 'hold'.OH