Mysql_real_escape_string() en pdo

<?php 
include('functions/membre.func.php');
include('body/header.php');
include('body/menu.php');

 
  if(isset($_GET['pseudo']) && !empty($_GET['pseudo']) && pseudo_incorrect()=== "1")
   {
	    if(isset($_POST['submit']))
		{
			$sujet =  mysql_real_escape_string(htmlentities(trim($_POST['sujet'])));
			$message = $sujet =  mysql_real_escape_string(htmlentities(trim($_POST['message'])));
              if(!empty($sujet) && !empty($message))
			  {
				  //
			  }else{
				  ?>
				     <div class='error'>Le sujet et le message sont obligatoires</div>
				  <?php
			  }
	    }
   }else{
	   header("Location:index.php?page=membre");
   }  
 
?>
<h3>Envoyer un message </h3>
<form method='post' action="">
<label for='a'>à : </label>
<input type="text" name='a' id='a' value='<?php echo $_GET['pseudo']; ?>' disabled='disabled'><br />
<label for='sujet'>Sujet : </label>
<input type="text" name="sujet" id='sujet'><br />
<label for='message'>Votre message : </label>
<textarea rows='6' cols='30' name='message' id='message'></textarea><br /><br />
<input type='submit' value="Envoyer" name='submit'>
</form>

$sujet =  mysql_real_escape_string(htmlentities(trim($_POST['sujet'])));
			$message = $sujet =  mysql_real_escape_string(htmlentities(trim($_POST['message'])));