WHITEHOUSE STATION, N.J. (AP) ¿ Merck & Co. and Santarus Inc. said Tuesday the Food and Drug Administration approved Merck's over-the-counter version of the Santarus prescription heartburn drug Zegerid. San Diego-based Santarus had partnered with Schering-Plough Corp. on the over-the-counter version, and stands to receive a $20 million milestone payment based on the approval. It could also get up to $37.5 million in sales milestone payments, along with royalties on sales. Merck said Zegerid OTC will be available in the first half of 2010. The drug will be sold by the Schering-Plough Health Care Products division, which Merck acquired in November as part of its acquisition of the drug maker. The drug, which combines omeprazole and sodium bicarbonate, is intended to prevent heartburn by suppressing stomach acid for 24 hours. In aftermarket trading, Santarus stock jumped $1.44, or 33.6 percent, to $5.73. The stock rose 7.5 percent during the day to close at $4.29, and reached a 52-week high of $4.39 in intraday trading.