According to your code snippet you missing the 'include' part...
You should have some require/require_once statement at the top of your code...
require_once '../Zend/Db/Adapter/Pdo/Mysql.php';
The exact path depends on your installation of course...
You may read more about it here:
http://framework.zend.com/manual/1.10/en/zend.db.adapter.html[
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