US Stocks Off After Merck Recall,Oil Rise  NEW YORK (Reuters) - U.S. stocks were knocked lower on  Thursday after drug maker Merck   Co.&lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MRK.N target=/stocks/quickinfo/fullquote"&gt;MRK.N&lt;/A&gt;, a member of the  blue-chip Dow, recalled its widely sold Vioxx arthritis drug  and oil resumed its climb to \$50 a barrel.