Schering-Plough ( SGP) said Friday that it would turn its blockbuster allergy drug Claritin into an over-the-counter medicine. Until now, the Kennilworth, N.J.-based drug maker has been resisting outside efforts to make Claritin available without a doctor's prescription. But in recent weeks, it's become clear that key government officials, most notably Health and Human Services Secretary Tommy Thompson, were amenable to such a switch. And Schering-Plough faces imminent generic competition when Claritin's patent expires in December. By voluntarily pushing Claritin over the counter, Schering-Plough will make lemonade from lemons. It will be able to keep generic copies of the drug off the market for another three years. And while Claritin will no longer command prices that enabled sales to reach $2.7 billion last year, a larger consumer base for a cheaper, over-the-counter version should still bring upward of $400 million annually, analysts say. Schering-Plough said Friday it filed a supplemental new drug application with the Food and Drug Administration seeking permission to make the Claritin switch. The company expects the agency to approve the application by the end of November. Details about new pricing were not disclosed.