UPDATE 2-Amgen quarterly profit tops expectations despite sales decline

(Adds analyst comment, sales details; updates shares)

Oct 25 (Reuters) - Amgen Inc reported higher-than-expected third quarter profit on Wednesday as lower costs and improved operating margins helped offset sales declines in some of its most important products.

The world's largest biotechnology company also raised its full-year adjusted earnings forecast, but its shares fell in late trading as weaker-than-expected sales of a new drug and declines in sales of key blockbuster products may have spooked investors.

Amgen boosted its earnings outlook to $12.50 to $12.70 per share from $12.15 to $12.65 despite taking a financial hit to Puerto Rico operations from Hurricane Maria, which devastated the island last month.

Analysts on average were looking for 2017 earnings of $12.58 per share, according to Thomson Reuters data.

The low end of Amgen's 2017 revenue forecast range was slightly raised to $22.7 billion from $22.5 billion with the top end still at $23 billion.

Amgen shares, up 21 percent this year, fell 2.2 percent to $173.50.

"Repatha, which is a key new launch drug for Amgen, is disappointing," said Cowen and Co analyst Eric Schmidt about the expensive cholesterol drug struggling to reach patients being repeatedly denied by insurers.

Repatha sales of $89 million were well short of analyst estimates of $106 million.

Sales of Amgen's two biggest products, Enbrel for rheumatoid arthritis and Neulasta, which prevent infections in cancer patients, each fell 6 percent.

Enbrel sales of $1.36 billion, in line with analysts' expectations, declined primarily due to increased competition.

Neulasta fell to $1.12 billion as new, less toxic cancer drugs led to declines in use of chemotherapy agents that increase infection risk.

Prolia for osteoporosis was a bright spot with sales up 22 percent at $464 million.

Amgen estimated the cost to 2017 earnings of restoring full operations in Puerto Rico would be 15 cents to 18 cents per share over the third and fourth quarters, with no expected disruption to product supply.

It does not anticipate hurricane damage to significantly impact 2018 results.

The company said its Puerto Rico drug substance manufacturing and packaging plants are fully operational, with formulation/filling and small molecule commercial production to resume by next week. It is still operating with generators due to extensive damage to the island's electrical grid.

Overall revenue declined 1 percent to $5.77 billion, about in line with Wall Street estimates.

But research and development spending, cost of sales and selling, general and administrative expenses were all lower.

Amgen posted third-quarter net profit of $2.02 billion, or $2.76 per share, up from a profit of $2.01 billion, or $2.68 per share, a year ago.

Excluding item, Amgen said it earned $3.27 per share, topping analysts' average expectations by 16 cents. (Reporting by Bill Berkrot; Editing by Meredith Mazzilli)