Germany's largest drugmaker Bayer gave a 2013 underlying earnings forecast that was slightly below analyst expectations amid competition for one of its most promising new drugs.

Bayer, which celebrates its 150th anniversary this year, said on Thursday it expected growth in adjusted earnings before interest, tax, depreciation and amortisation (EBITDA) in the mid single-digit percentage range, compared with analysts' expectations of about 8%.

A strong rival for Bayer's stroke prevention pill Xarelto has emerged in the form of Bristol Myers-Squibb and Pfizer's Eliquis. The competing product was approved in the United States in December.

That still leaves Bayer's pipeline of new treatments - which includes eye drug Eylea against the leading cause of blindness among the elderly - the envy of many in the industry.

The prospect of future drug sales has shored up its market value including net debt as a multiple of expected core earnings to 7.7, to match the healthcare peer group according to Thomson Reuters StarMine.

That is even though diversified groups like Bayer - also a maker of plastics and farming pesticides - usually trade at a discount to pure-play rivals.

Bayer, the inventor of Aspirin, said it expects its healthcare unit, with its prescription, over-the-counter and animal health drugs, to see sales grow by 6% per year to €22 billion by 2015, excluding currency swings and portfolio changes, up from 18.6 billion in 2012.

Fourth-quarter adjusted EBITDA rose 18.4% to €1.825 billion ($2.39 billion), in line with the average estimate in a Reuters poll.

Quarterly sales of €9.86 billion were slightly above expectations.