Amgen Inc. posted conservative guidance for 2019 as it faces generic and biosimilar competition on several of its growth drivers.

Calcium reducer Sensipar is one of the major products, in addition to Neulasta, that is facing such competition. Sales of the treatment rose 3% for the full year of 2018. Others that led to the reduced guidance were autoimmune drug Enbrel — which is mired in a court battle with a biosimilar from Novartis AG — and bone marrow stimulant Aranesp.

"If not for Sensipar, perhaps our guidance would have been a little bit better than traditionally would be the case, including the uncertainties around the path for Neulasta which is obviously an important part for us," Amgen CEO Robert Bradway said.

The scenario is not new for Amgen — in the fourth quarter, sales of the company's precursor to Neulasta, called Neupogen, fell 40% due to biosimilar competition.

The company posted a strong fourth quarter beat for 2018 on the shoulders of product sales that exceeded expectations. But like that of other companies in the pharma sector, its guidance for 2019 is more conservative than analysts had predicted.

Amgen's revenue rose 7% in the quarter and 4% for the full year to $23.7 billion.

The company expects total revenue in 2019 of between $21.8 billion and $22.9, a projected loss year over year that executives arrived at by taking into account generic and biosimilar competition on some of its most profitable products.

Drug sales beat on volume

Drug sales at Amgen were particularly stronger than expected for three of the Thousand Oaks, Calif.-based company's products: cholesterol treatment Repatha, bone cancer drug Neulasta and its new migraine drug Aimovig.

Amgen pulled in $159 million with Repatha in the fourth quarter, a 62% increase year over year. Executives on the call noted that Repatha achieved the result despite a sharp list price decrease of 60%, a testament to the drug's sales volume.

For the full year, the PCSK9 drug rose by 72% while nearly doubling its volume over 2017's number.

"We have seen strong uptake of [Repatha], representing over 25% of all units in the U.S. as we exited the fourth quarter," said Murdo Gordon, executive vice president of global operations during the company's Jan. 29 earnings call.

Cancer drug Neulasta also prevailed in the face of major headwinds in the form of biosimilar competitors from Mylan NV and Coherus Biosciences Inc. Even as these copycats hit the market in 2019, annual sales of Neulasta declined by only 1%, well above consensus estimates.

"As we anticipated, we now have two biosimilar competitors in the U.S., facing one competitor during [the fourth quarter], and we retain 96% share of the long-acting market," Gordon said. He added that 2019 should show more sales erosion, however.

One of the bigger surprises was Amgen's migraine drug Aimovig, approved in May 2018. The treatment, one of three approved around the same time, was offered for free to half of the patients, but still netted $95 million in the fourth quarter against consensus estimates of only $50 million.

The drug faces two competitors in the class from Eli Lilly and Co. and Teva Pharmaceutical Industries Ltd.

"We expect Aimovig to continue to be a growth driver for Amgen," Gordon said.

M&A on the horizon?

Bradway also said that Amgen would be open to the possibility of making a deal in 2019.

"We're looking across the waterfront to find ways to invest in the industry we think can add value to shareholders, not just the target shareholders," Bradway said.