Amgen beat second-quarter estimates and raised its guidance, sending the stock up in after-hours trading. Earlier Thursday, fellow big biotech Alexion Pharmaceuticals also beat views but its guidance worried the Street.

Amgen (AMGN) earnings grew 8% vs. a year earlier to $2.57 a share, beating analysts' target by 14 cents, according to Thomson Reuters. Revenue rose 4% to $5.37 billion, the smallest gain since Q4 2011 but about $19 million above consensus.

The biotech raised its full-year EPS guidance to $9.55 to $9.80, up from $9.35 to $9.65 but roughly in line with what Wall Street already expected. It raised revenue guidance slightly to $21.1 billion to $21.4 billion, on the high side of analysts' $21.17 billion.

Amgen's best-selling drug Enbrel's global sales rose 8% year-over-year to $1.28 billion, vs. consensus of $1.25 billion, according to Evercore ISI. The company largely credited price increases. Its second-biggest moneymaker, the Neupogen/Neulasta franchise, performed in line. Epogen missed estimates as it faced increasing competition.

Operating Margins Strong "The 2Q EPS beat appears to be primarily driven by a second consecutive quarter of above-consensus operating margin — 49% vs. consensus 47%," wrote Evercore analyst Mark Schoenebaum in an email to clients.

Amgen also appointed Warburg Pincus partner Fred Hassan to its board of directors. Hassan was CEO of Schering-Plough when it sold to Merck (MRK) in 2009 for $41 billion.

"Investors will wonder if this adds any aspect to M&A thoughts," remarked RBC Capital Markets analyst Michael Yee in a brief research note.

Amgen stock rose 2% to 175.25 in late trading, after rising 0.1% in regular trade to 171.69. Amgen hit a record 174.80 Tuesday.

Earlier, Alexion (ALXN) said its earnings rose 29% over a year earlier to $1.44 a share, beating analysts' views by 6 cents. Revenue grew 24% to $636 million, about $8 million above consensus.

Alexion lifted and tightened its full-year revenue outlook slightly, from $2.6 billion to $2.62 billion, but that's still a hair below the consensus for $2.63 billion.

The company also adjusted its guidance on expenses to reflect the acquisition of Synageva BioPharma, which closed June 22. Alexion added some $140 million to its expense guidance, on both the R&D and SG&A lines. On the other hand, the effective tax rate was guided lower to just 3%-4%.

All of this activity added up to a dollar being cut off of EPS guidance, now $4.70-$4.80 vs. analysts' $4.98.

Alexion stock fell 5% intraday, but closed up 0.3% at 199.29.

Alexion Awaits Key Drugs Synageva's lead drug, Kanuma, is still going through the approval process in the U.S. and the EU. Alexion paid a controversial 135% premium on Synageva's market value at the time, based on its belief that Kanuma, which treats a rare disease called lysosomal acid lipase deficiency, will top $1 billion in annual sales.

On Alexion's earnings conference call with analysts, CEO David Hallal said that although he expects Kanuma to launch this year, the liftoff of drugs for ultrarare diseases is normally "slow and steady." Alexion experienced the same thing with Soliris, which eventually became a blockbuster and currently provides all of its revenue.

Also on the call, Alexion CFO Vikas Sinha said that the buyout's impact will hit especially hard in Q3, which he also guided below consensus. He sees revenue of $662 million to $665 million, vs. the Street's estimate of $668 million, with EPS of 90-95 cents, well below analysts' $1.13.

Bernstein analyst Geoffrey Porges needled management about both the costs and the continually receding launch of Strensiq, another rare-disease drug that Alexion had originally guided in the first half of this year.

Hallal admitted that things had not worked out quite as planned, but since the drug has already been approved in Japan and got a positive vote from the European Medicines Agency's advisory panel, he still expects the FDA to ultimately approve the drug.