NEW YORK (AP) ¿ Shares of Santarus Inc. soared in premarket activity Wednesday after the Food and Drug Administration approved an over-the-counter version of the company's prescription heartburn drug Zegerid. The stock gained $1.13, or 26.3 percent, to $5.42 ahead of Wednesday's market open. The stock has ranged from $1.05 to $4.39 over the past year. The company had partnered with Schering-Plough Corp. on the over-the-counter version of Zegerid. Merck & Co. took over the application after buying Schering-Plough in November. San Diego-based Santarus stands to receive a $20 million milestone payment and could also get up to $37.5 million in sales milestone payments, along with royalties on sales. Santarus recorded revenue of $130.2 million in 2008. Merck said Zegerid OTC will be available in the first half of 2010.