Using 'distinct' in a MySQL query

"SELECT p.author_name, p.author_id, DISTINCT p.topic_id, t.title
        							FROM `ibf_posts` p, `ibf_topics` t WHERE p.topic_id = t.tid  ORDER BY pid DESC LIMIT 8"

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'DISTINCT p.topic_id, t.title FROM `ibf_posts` p, `ibf_topics` t WHERE p' at line 1

SELECT DISTINCT ...