Image source: Getty Images. What: Progenics Pharmaceuticals (NASDAQ: PGNX) is up 23% at 3:35 p.m. ET after announcing yesterday after the closing bell that the Food and Drug Administration approved an oral version of the company's opioid-induced constipation drug, Relistor. So what: In 2011, the biotech licensed Relistor to Salix Pharmaceuticals, which was bought by Valeant Pharmaceuticals (NYSE: VRX) last year. Valeant Pharmaceuticals already sells an injectable version of Relistor, but it isn't a particularly big seller with sales of just $16.6 million in the first quarter, netting Progenics Pharmacetuicals $2.2 million in royalty revenue. The new oral version, which Valeant will start selling in the third quarter, will be easier for patients to take than the injected version, resulting in higher sales. As part of the deal with Salix, Progenics Pharmaceuticals is due $50 million upon approval of oral Relistor in the U.S. and could get up to $200 million in commercial milestones based on annual sales. The royalty rate also increases as sales increase with tiers at annual sales of $100 million, $400 million, and $500 million. Now what: Progenics management believes the oral version of Relistor could be a $1-billion-plus opportunity for Valeant, according to an analyst report from Guggenheim's Louise Chen. Even if that's a bit of a stretch, half of that estimate would be a welcome increase in royalty revenue for Progenics Pharmaceuticals to help develop the rest of its pipeline.A secret billion-dollar stock opportunity The world's biggest tech company forgot to show you something, but a few Wall Street analysts and the Fool didn't miss a beat: There's a small company that's powering their brand-new gadgets and the coming revolution in technology. And we think its stock price has nearly unlimited room to run for early in-the-know investors! To be one of them, just click here.Brian Orelli has no position in any stocks mentioned. The Motley Fool owns shares of and recommends Valeant Pharmaceuticals. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.