Merck & Co., the world's biggest drug maker, said it will split its stock 2-for-1 in February, its first split since 1992, as prospects for its new painkiller push its shares to record prices. Merck said it has filed with the Food and Drug Administration for approval of its drug Vioxx, which appears to treat pain and swelling without irritating the stomach. Analysts estimate the drug could top $1 billion in annual sales. Although rival Monsanto Co. may beat Merck to market with Celebrex, a similar drug, Merck should catch up quickly. Its drug offers once-a-day dosage while Celebrex is taken twice a day. Shares of Whitehouse Station, N.J.-based Merck rose $2.63 to close at $158.63 on the NYSE.