FDA to Pfizer: Pull Wild Thing Viagra Ad  WASHINGTON (Reuters) - Two television advertisements for  Pfizer Inc.'s &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=PFE.N target=/stocks/quickinfo/fullquote"&gt;PFE.N&lt;/A&gt; impotence drug Viagra should be withdrawn  for claiming a return of sexual desire and omitting  key  information, the Food and Drug Administration said in a letter  to the company released on Monday.