PDOにPEAR_DB形式のDSNを渡しても大丈夫なように ref: http://qiita.com/items/ebed1e6b8df805c4f580

myPDO.php

<?php
class SQLDB extends PDO{
    public $database_name;
    public $DSN;
    public $USER;
    public $PASS;
    public function __construct($DSN,$USER=null,$PASS=null){
        if($this->is_pear_db_style_dsn($DSN)){
            list($DSN,$USER,$PASS) = trans_pear_db_DSN_to_pdo_dsn($DSN);
        }
        if($USER=null||!$PASS=null){
            throw new Exception("USER/PASSがnullです。".
            "DBのユーザー名とパスワードを省略するときは、空文字 PASS=''を与えて下さい ");
            exit;
        }
        parent::__construct($DSN,$USER,$PASS);
        $this->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        $this->DSN  = $DSN;
        $this->USER = $USER;
        $this->PASS = $PASS;
    }
    //PEAR DB 形式のDSNか判定する。
    public function is_pear_db_style_dsn($dsn){
        //PEAR DSNは、URL形式なのでURL形式でパースして、結果がNULLでなければ、
        //PEAR::DB形式と断定
        return array_key_exists("hash", $parse_url($dsn));
    }
    //PEAR DB 形式のDNSをPDO形式に変えてしまう
    public function trans_pear_db_DSN_to_pdo_dsn($DSN){
        $dsn = $DSN;
        $hash = parse_url($dsn);
        $dsn_array = array();
        $dsn_array["driver"] = $hash["scheme"];
        $dsn_array["host"] = $hash["host"];
        $dsn_array["db_name"] = str_replace("/","",$hash["path"]);
        $dsn_array["user"] = $hash["user"];
        $dsn_array["pass"] = $hash["pass"];
        //var_dump($hash);
        //var_dump($dsn_array);exit;

        $PDO_DSN = "{$dsn_array['driver']}:host={$dsn_array['host']};dbname={$dsn_array['db_name']}";
        $PDO_DB_USER = $dsn_array["user"];
        $PDO_DB_PASS = $dsn_array["pass"];
        return array(
            "DSN"         => $PDO_DSN,
            "USER" => $PDO_DB_USER,
            "PASS" => $PDO_DB_PASS,
        );    
    }

}