- preg_replace: documentation ( source)
<?php
$input = '[protected-iframe id="76d9c935529099f1c2c4c20af7fa9da1-55735640-4908649" info="http://embed.sendtonews.com/player2/embedcode.php?fk=t4GWIwRy&cid=6174" class="s2nPlayer-t4GWIwRy" width="560" height="340"]';
$output = preg_replace( '#\[protected-iframe(.*)?info="https?://(www\.)?embed\.sendtonews\.com(.*)?"(.*)?\]#', '', $input );
echo $output;