Custom GET Parameters In Plugin’s Admin Page

by

I’d recommend using add_query_arg():

  $url = add_query_arg(array(
            'foo'=>'bar',
            'custom'=>'var',
            'page'=>'myadminpage'
           ), admin_url('admin.php'));

The second argument, admin_url('admin.php'), is optional – and if omitted it uses the url of the current page you are on.