* Q2 sales and earnings beat estimates

* Raises full-year forecast

* Extends series of positive quarterly results

* Investor concerns on pipeline, Zantac claims

(Adds graphic, details in paragraph 3 and 7-9, background in paragraphs 5-6, investor comment in paragraphs 11-12)

LONDON July 26 - GSK raised its full-year profit and sales guidance on Wednesday after its second-quarter earnings beat expectations, helped by strong sales of its shingles vaccine Shingrix and HIV medicines.

The London-listed drugmaker now expects adjusted earnings per share growth of 14%-17% for the year, up from its earlier expectations of 12%-15%.

The company now expects sales to increase by 8% to 10% this year, compared with 6% to 8% previously and for adjusted operating profit to increase between 11 to 13%, up from 10% to 12%.

"We have delivered another excellent quarter of performance, with strong sales and earnings growth, notably in HIV and vaccines, and continued strengthening of the R&D pipeline and product portfolio," CEO Emma Walmsley said in a statement.

The better-than-expected results may further help revive investor confidence in Walmsley's strategy, coming a year after the company spun off its consumer health business, Haleon, in its most radical shake-up in 20 years.

The British drugmaker has lagged rivals in recent years, with some investors and analysts worried about the strength of its pipeline of drugs in development and costly U.S. litigation over discontinued heartburn drug Zantac.

The company also reported an adjusted profit of 38.8 pence per share for the quarter, on sales of about 7.18 billion pounds ($9.26 billion).

Analysts were expecting a profit of 34.7 pence per share on sales of about 6.77 billion pounds, according to company-compiled consensus estimates.

Sales of Shingrix, the company's top-selling drug, generated 880 million pounds, beating analyst estimates of 872 million pounds.

The results highlighted the strength of GSK's underlying business driven by HIV and vaccines, Dani Saurymper, a portfolio manager at Pacific Asset Management, and a GSK shareholder, said.

But without an update on the Zantac litigation or change in pipeline outlook, the shares may continue to lag peers, he said.

($1 = 0.7754 pounds)

(Reporting by Maggie Fick in London and Radhika Anilkumar in Bengaluru; Editing by Janane Venkatraman, Savio D'Souza and Josephine Mason)