Recasts with share drop in paragraphs 1-3, adds analyst comment in paragraphs 4-6, adds sales graphic

By Bhanvi Satija

LONDON, April 29 (Reuters) - Strong first-quarter results under new GSK GSK.L CEO Luke Miels on Wednesday failed to impress investors, who raised concerns that the British drugmaker's performance was enhanced by one-off factors, sending its shares more than 8% lower.

Miels was appointed to convince investors that GSK can hit 2031 sales targets, boost its drug pipeline and navigate the looming 2028 patent expiry of its HIV medicine dolutegravir.

GSK shares have gained about 20% since he was named as CEO in September, including Wednesday's moves.

James Eugene, research analyst at Verso Investment Management, said the share price fall was likely due to "quality concerns around the earnings beat (that) will be in question given that they were driven by one-off factors".

Eugene, whose firm holds shares of GSK, also noted softer trends in GSK's general medicines business, which includes its older asthma drug Trelegy.

"Both of these factors mean that the beat is likely more modest than the numbers suggest," he said.

GSK posted core earnings per share of 46.5 pence for the three months ended March 31, compared with analyst forecasts of 43.3 pence.

Its shares were trading at 1,863 pence at 1432 GMT, wiping off some of this year's gains and putting GSK among the day's top fallers on the broader FTSE 100 .FTSE index.

AMBITIOUS TARGET

Miels, who was previously chief commercial officer, is under pressure to show GSK's research and development can deliver a revenue target of over 40 billion pounds ($54 billion) by 2031.

Analysts currently expect 35 billion pounds in sales that year and GSK's first-quarter revenue this year was 7.6 billion pounds, broadly in line with expectations.

Sales of GSK's specialty medicines, which include its HIV business and cancer treatments, were in line with estimates at 3.23 billion pounds.

Miels said he hopes to broaden GSK beyond its HIV business and stressed it is speeding up development of medicines, with 10 planned late-stage trials across its portfolio for this year.

Of those, five are trials of a targeted cancer therapy licensed from China's Hansoh Pharma 3692.HK.

"To simplify how we work, we're matching our best people and resources to the opportunities in front of us, and we're employing AI to accelerate this," Miels said.

GSK reviewed more than 50 late-stage programmes spanning oncology, HIV and other parts of its portfolio that showed value for speeding up or expansion and plans to share a shortlist and the rationale behind them in the second quarter.

Under Miels, GSK has increased bolt-on acquisitions, agreeing to buy U.S. biotech RAPT Therapeutics, which he said reflects the type of deal the company prefers.

GSK maintained its full-year forecast of 3% to 5% sales growth and core operating profit growth of 7% to 9%.

SHINGRIX SALES A BRIGHT SPOT

Sales of Shingrix were 1.03 billion pounds for the quarter, compared with expectations of 851 million pounds, helped by higher demand in European markets and the launch of the new pre-filled, more convenient format of the shot in the U.S.

Barclays estimated stocking provided a 100 million pound benefit.

Miels said GSK has shifted its Shingrix strategy to focus on patients with other co-morbidities such as diabetes or heart conditions.

Overall vaccine sales of 2.15 billion pounds also came in ahead of expectations of 2.03 billion pounds.

In a note titled 'Vaccines save Q1', HSBC analysts wrote that Shingrix performance more than made up for a small miss in cancer drug sales.

($1 = 0.7405 pounds)