(Reuters) - Amgen Inc on Tuesday reported fourth-quarter profit that easily surpassed expectations as sales rose and tax expense fell, but competition for its older medicines is growing and the drugmaker forecast 2019 earnings below Wall Street estimates.

FILE PHOTO: An Amgen sign is seen at the company's office in South San Francisco, California in this October 21, 2013 photo. REUTERS/Robert Galbraith/File Photo

Shares of Amgen, the world’s largest biotechnology company, were down 2.3 percent at $187.65 in after-hours trading.

For the full-year, Amgen projected adjusted earnings of $13.10 to $14.30 per share on revenue of $21.8 billion to $22.9 billion. Wall Street analysts, on average, had forecast $14.61 per share on revenue of $22.9 billion, according to IBES data from Refinitiv.

Speaking on a conference call, Chief Financial Officer David Meline said Amgen faces headwinds in the form of competition for legacy products such as kidney drug Sensipar and rheumatoid arthritis treatment Enbrel as well as heightened U.S. focus on the issue of prescription drug affordability.

He said Amgen’s 2019 outlook assumes its global net sales prices will drop by a rate in the “mid-single digits” after falling 1 percent in 2018.

Excluding items, Thousand Oaks, California-based Amgen posted adjusted quarterly earnings of $3.42 per share, topping analysts’ average expectations by 15 cents.

Revenue for the quarter rose 7 percent to $6.23 billion, beating the average analyst estimate of $5.84 billion.

“The fourth quarter was a very strong result,” said Jefferies analyst Michael Yee.

“The (2019) guidance reflects an expected year of uncertainty and some lack of visibility” regarding competition from cheaper biosimilar versions of white-blood-cell booster Neulasta and Enbrel - Amgen’s two biggest-selling products.

Amgen’s forecast appears to be part of an emerging trend among large drugmakers. Earlier on Tuesday, Pfizer Inc issued a 2019 earnings forecast well below Wall Street estimates. That followed lower-than-expected initial full-year earnings outlooks from Johnson & Johnson and Bristol-Myers Squibb Co

However, Yee noted that Amgen has historically issued conservative financial forecasts at the beginning of the year, before raising them each quarter as actual results are reported.

The increase in Amgen’s fourth-quarter sales was driven largely by demand for medicines such as cancer drug Kyprolis, cholesterol fighter Repatha and osteoporosis treatment Prolia.

Sales of new migraine drug Aimovig totaled $95 million for the quarter, nearly double the $50 million analysts had forecast. Aimovig was first to market among a new class of drugs designed to prevent rather than treat migraine headaches.