NEW YORK (AP) — King Pharmaceuticals Inc. extended its $37-per-share buyout offer for Alpharma Inc. on Monday and has already acquired about 92 percent of the company’s outstanding stock. The offer is now extended to 10.a.m. Dec. 29. It was set to expire Dec. 19.Bridgewater, N.J.-Alpharma agreed to Bristol, Tenn.-based King’s $1.6 billion cash takeover offer in November, ending the drugmakers’ months-long battle. The offer represented a 54 percent premium to Alpharma shareholders. Alpharma previously rejected a $1.4 billion offer from King, which then raised its bid and said it would take the offer directly to shareholders. Both boards of directors have since unanimously approved the deal. As of Dec. 19, King had bought just over 38.6 million shares of Alpharma’s stock, representing 92.2 percent of shares outstanding. A key goal of the deal is to expand King’s pain drug franchise, which consists of the chronic pain treatment Avinza and the muscle relaxant Skelaxin. They made up about half of the company’s revenue in 2007. Alpharma gets most of its revenue from animal health products, though the bulk of its pharmaceutical sales come from the morphine painkiller Kadian. It also launched the Flector Patch, a pain treatment, in January. King, meanwhile, is developing the abuse-resistant pain drug Remoxy with partner Pain Therapeutics Inc. while Alpharma has a tamper-resistant morphine pill called Embeda under review. Credit Suisse and Wachovia Securities are acting as financial advisers, and Dewey & LeBoeuf LLP is acting as legal counsel to King.