multiple db connections with ezSQL v2

Am trying to work out how to have multiple db connections in ezSQL 2.x.

I use an include file which has all my sql queries in it.
At the top of it I thought I could do

$db_users = new ezSQL_mysql('user','user_pw','users','localhost');
$db_pubs = new ezSQL_mysql("user", "user_pw!", "publications", "localhost");

then do

function GetUsers()
{
global $db_users;
$GetUsers = new ez_select();
$GetUsers ->add_table("user_details");
$GetUsers->add_field("user_ID");
$SQL_query = $GetUsers->make();
return($SQL_query);
}
function GetPubs()
{
global $db_pubs;
$GetPubs = new ez_select();
$GetPubs ->add_table("pubs");
$GetPubs ->add_field("pub_ID");
$SQL_query = $GetPubs ->make();
return($SQL_query);
}

But when I run it, when it comes to GetPubs, it says no table pubs in user database - which I know.

Hints?

thanks