Array from form to DB insert

[lurking]

I have a form that lists a bunch of names with a checkbox next to each one. If the checkbox is checked, the data is inserted into my DB.  Whereas previously, the checkbox value was just a variable (user_ID), now I need it to be an array to pass two variables (user_ID + db_designation):

[code]<input name="user_ID[]" type="checkbox" id="user_ID[]"
value="<?php echo urlencode(serialize(array($row_rsPhysicianDetails['user_ID'],
$row_rsPhysicianDetails['db_designation']))); ?>" />[/code]

I grab the array data via:
[code]<?php $user_id_array = $_POST['user_ID']; ?>[/code]

and then have been attempting to insert into my database with a foreach() and nested if() loop.

[code]<?php if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "attendance")) {
  foreach($user_id_array as $value)
  {
  list($user, $designation) = unserialize($value);
  if ($designation == "p") {
  $query = "INSERT INTO course_complete (user_ID, course_ID, course_date, credit_hours, course_session)" .
"VALUES($user, '$c_ID', '$c_date', '$credit_hours', '$course_session')";
  @mysql_query($query);
  }
  }
?>
[/code]

At this time, the insert is not working.  Also, when I tried to see if the data was even being collected via:

[code]
<?php
$user_id_array = $_POST['user_ID'];
echo '<pre>';
print_r($_POST);
echo '</pre>';
?>
[/code]

the result was an empty array:

Array
{
}

I would appreciate any ideas for making sure the variable $user_id_array is populating appropriately, and then making the insert work with the foreach, if, serialize and list syntax.  Thank you.