Interesting issue here.
I have this under a vhost along with many other rewritecond's that work fine.
<code>
RewriteEngine on
rewritecond %{query_string} page_id=20 [nc]
rewriterule ^(.*)$
http://newurl.com [r=301,nc]
</code>
This doesn't seem to work after reloading Apache's config. According to documentation, this should work; any ideas?