KINGS MOUNTAIN, N.C. — Since the launch of Nexium 24HR in May of 2014, the brand has generated approximately $300 million, “making it one of the largest and most successful Rx-to-OTC switches,” Ian Read, Pfizer chairman and CEO, recently told analysts. Indeed, on its current sales pace, Nexium 24HR will supplant the reigning antacid Prilosec OTC by summer’s end, making it the best-selling gastrointestinal solution on the market.