GlaxoSmithKline Plc (GSK - Get Report) reports fourth-quarter earnings Wednesday, with investors looking for guidance on the fate of its key Advair drug in the U.S. and the recent pace of organic growth for new products sales.

The group is expected to announce earnings per share of £0.24 on sales of £7.48 billion ($9.25 billion) for the three months ending in December, according to Factset estimates. Net profit for the quarter is forecast at £1.1 billion, up from a £354 million loss in the year-ago period. For the full year, analysts see sales of £27.7 billion and earnings per share of £1.01.

Currency tailwinds are expected to play a significant role in the company's top and bottom line, however, with the company's reporting currency, the pound, falling 4.77% against the U.S. dollar over the October to December period. Glaxo takes one third of its sales from the United States.

"We expect GSK to deliver 16% Core EPS growth in 2017 but 14% of this will be FX tailwind... We therefore forecast 2.6% [constant exchange rate] growth as strong high single-digit underlying growth is impacted by generic Advair in the US," said Roger Franklin at Liberum Capital.

Perhaps more importantly, investors will be keen to hear further guidance on expectations surrounding Advair sales, because the drugmaker has seen a growing line of competitors threatening to encroach on its blockbuster asthma treatment over the last year.

In 2015 Advair pulled-in £3.7 billion in sales, down approximately 30% from their peak in 2013, but still accounting for 15% of total group sales.

But Mylan, Hikma Pharmaceuticals (HKMPY and Vectura (VEGPF all have generics sat pending approval from the FDA. Mylan expects to be first out of the gate with a decision on its own drug due by March 28.

"We now assume US Advair sales fall by 35% as Mylan and Hikma potentially enter the market around mid-year," said Berenberg analyst Alistair Campbell in a recent note.

Credit Suisse analysts are forecasting a 40% decline in the U.S. revenue stream during 2017 and the team at Liberum Capital in London projecting a 50% decline.

Recent sales growth and future expectations for Glaxo's 'new products' will also be a key focus point. The segment includes HIV treatments made under the ViiV joint venture, as well as new asthma and meningitis drugs.

It pulled in more than £2 billion of revenue in 2015 and management have forecast that it will add £6 billion to group sales before 2018, leaving it as Glaxo's best hope of being able to offset hole left in its top line by declining Advair sales.

GlaxoSmithKline shares were trading at 1,565 pence each at 12:45 GMT, up 0.59% on the session and putting them modestly into positive territory for the past three months compared to a 5.06% advance for the Stoxx Europe TMI Pharmaceuticals index. 

The London-listed firm has been among the greatest beneficiaries of the U.K's vote to leave the European Union, given the subsequent currency depreciation, although gains for the shares crimped in more recent months as investors fretted about the potential hit to future profitability if President Donald Trump were to clamp down on drug pricing.

The newly inaugurated leader met with pharma executives in the White House at the end of January, which culminated in a pledge to streamline the drug approval process, but omitted any detail of substance on what the administration will do about drug prices.