PHP codigniter ajax call to load dropdown when another dropdown changes

<select id="makes2" name="makes2" style="width:200px;" data-hint="" onchange="load_dropdown_content1($('#field2'), this.value)">
                          <?php 
$sql = mysql_query("SELECT distinct make FROM advertisements");
while ($row = mysql_fetch_array($sql)){
echo "<option value='".$row['make']."'>" . $row['make'] . "</option>";
}
?>

</select>



here my values are hard coded to load values from mysql database

when dropdown onchange() function following javascript function will be called

here my controller compareVehicles --> get_dropdown_values1 function is called asynchronously



<script type="text/javascript">


function load_dropdown_content1(field_dropdown1, selected_value1){
   var result = $.ajax({
        'url' : '<?php echo site_url('compareVehicles/get_dropdown_values1'); ?>/'+selected_value1,
        'async' : false
    }).responseText;
    field_dropdown1.replaceWith(result);





}


inside the controller my function as follows



function get_dropdown_values1($filter11){

        $this->load->model('model_c/cmp_vehi_model');

        $result1 = $this->cmp_vehi_model->get_options1($filter11);

foreach($result1 as  $key1 => $value1){

$final1 = array('{$key1}' => $value1);

}

        $this->load->helper('form');

       
echo "<select name=\"field2\" id=\"field2\" onchange=\"load_dropdown_contentad($('#field5'), this.value);\" onblur=\"load_dropdown_contentad($('#field5'), this.value);\"  onfocus=\"load_dropdown_contentad($('#field5'), this.value);\"  style=\"width:200px\"  >";
    

foreach($result1 as  $key1 => $value1){
echo"<option value='{$value1}'>{$value1}</option>";
}

echo "</select>";


    }





model that is calling from controller as follows


function get_options1($filter11){

$query1 = $this->db->query("SELECT distinct modelnumber FROM advertisements WHERE make LIKE '".$filter11."'");
$result1 = $query1->result_array();

$x1 = array();
foreach($result1 as $i1){

array_push($x1, $i1['modelnumber']);

}


 
        return $x1;

    }



in my controller php code is  echo to load ajax called dropdown
Please go to following link to see how it works
http://sep06.netne.net/online_portal/index.php/controller_c/compareVehicles/cmpVehicles