$this->fetchMultiKarma = $this->db->prepare('
    SELECT word, karma, ROWID id FROM karmas WHERE word IN ( :words ) ORDER BY karma DESC
');

// Construct the PDO query and retrieve the results
$wordsin = "'".implode("','", $words)."'";
$res = $this->fetchMultiKarma->execute(array(':words'=>$wordsin));
while (($row = $res->fetch(PDO::FETCH_ASSOC))) {
    $this->doPrivmsg($source, 'Debug: '.$row['word'].' => '.$row['karma']);
}