Lawmakers Question Merck, FDA Over Vioxx  WASHINGTON (Reuters) - A leading U.S. Senate Republican  this week demanded internal documents from Merck   Co. Inc.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MRK.N target=/stocks/quickinfo/fullquote"&gt;MRK.N&lt;/A&gt; that could answer questions about the company's  interaction with U.S. regulators over its arthritis drug Vioxx.