$client = new IXR_Client('http://othersite.com/xmlrpc.php');
I get the error
Fatal error: Class 'IXR_Client' not found in footer.php
I can see the class in wp-includes/class-IXR.php, and I've checked that the path to this file is correct in wp-includes/functions.php as per this discussion.
Am I missing something needed to use this class in my custom theme's footer?