Biotech company Amgen Inc. beat analyst estimates in the first quarter, with a 6 percent increase in sales of its arthritis and osteoporosis drugs. The Thousand Oaks company reported net income of $1.5 billion ($1.96 a share) in the quarter ended March 31, compared with $1.61 billion ($1.61) in the same period a year earlier. Revenue rose 5 percent to $4.24 billion. Excluding certain items, the company reported earnings of $1.88 a share, which topped the consensus estimate of 23 analysts by 4 cents, according to Thomson/First Call. However, revenue fell short of estimates by $130 million. Osteoporosis drug Prolia saw the best gains, with sales up 61 percent to $142 million. Sales of Aranesp, its popular anemia drug, were down 10 percent to $468 million. The company has been forced to make marketing changes after it pleaded guilty to marketing Aranesp for off-label uses last year. It also settled a charge earlier this month that it was providing kickbacks to care providers who prescribed it to patients. The blockbuster anemia drugs Neulasta and Neupogen still accounted for its largest percentage of sales, together bringing in $1.34 billion. The company continued to see higher R&D expenses, which rose 18 percent during the quarter. The increase is due to a focus on a broad pipeline of development-stage drugs, the company said in its report. “We are on track to deliver out full-year growth objectives,” said Chief Executive Robert Bradway, in a statement. “In addition, our key pipeline projects are progressing well and we are looking forward to clinical results from on-going trials.” Shares of Amgen have traded at record highs in recent weeks, in part due to an aggressive stock buy-back program. During the quarter, the firm repurchased 9 million shares at an average price of $85.03. It said in its earnings report that it has $1.6 billion remaining under a previously-authorized stock repurchase plan. Shares lost 66 cents, or less than 1 percent, to close at $112.76 on the Nasdaq.