Stocks End Lower as Pfizer and Oil Weigh  NEW YORK (Reuters) - U.S. stocks closed lower on Friday,  weighed down by a number of negative reports from top drug  makers, including Pfizer Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=PFE.N target=/stocks/quickinfo/fullquote"&gt;PFE.N&lt;/A&gt;, and a \$2 jump in the  price of crude oil.