Jquery: Refreshing DropDownLists in UpdatePanel

I have been trying for days to call my vb code from jquery function.  I am getting the Panel to update but call is not being made see code below and please advise.

Jquery:
 function addDDLOpenDialog(orgID, tableName) {
        var divName = "#OtherMedicationDialog";
        var ajaxUrl = "CRE.aspx/AddOtherMedication";
        $(divName).dialog("destroy");
        $(divName).dialog("open");

        $(divName).dialog({
            autoOpen: "false",
            title: "Add List Value",
            width: 500,
            height: 235,
            modal: true,

            //Define Buttons
            buttons: {
                Submit: function () {
                    var newValue = "";
                    newValue = $("#<%= omDialogTB.ClientID  %>").val();
                    //Submit form by calling webservice
                    $.ajax({ type: 'POST',
                        url: ajaxUrl,
                        data: '{orgID:"' + orgID + '", tableName:"' + tableName + '", newValue:"' + newValue + '"}',
                        contentType: "application/json; charset=utf-8",
                        dataType: "json",
                        success: function (msg) {
                            if (msg.d) {
                                //"ClientScript.GetPostBackEventReference(btnRefreshDDL, '')";
                                __doPostBack('<%= btnRefreshDDL.ClientID%>', '');
                            }
                        },
                        error: function () {
                            alert("Error! Try again...");
                        }
                    });
                    //Now close dialog
                    clearForm(divName);
                    $(this).dialog('close');
                },
                Close: function (ev, ui) {
                    clearForm(divName);
                    $(this).dialog('close');
                }
            }
        });          //end of Dialog w/options
    };  //End of openDialog Function 

aspx:
 <asp:UpdatePanel ID="MedicationInfoUP" runat="server" UpdateMode="Conditional" >
                              <ContentTemplate>
                              <asp:LinkButton runat="server" ID="btnRefreshDDL" OnClick="MedicalInfoUpdatePanel" style="display: none;" />
                                <div class="MIContent">                          
                                <!-- Beginning of Fieldset -->

Code behind:
 Protected Sub MedicalInfoUpdatePanel(ByVal sender As Object, ByVal e As System.EventArgs)
        'Retrieve Data from LINQ Datasource
        Dim db As ClientInfoDataContext = New ClientInfoDataContext
        'check to see if userID already exist.  If So then Basic Record exist already only updates are necessary
        'return userID by providing BadgeID
        Dim userID As String = ""
        If Not (String.IsNullOrEmpty(Request.QueryString("ID"))) Then
            userID = Request.QueryString("ID").ToString()
        End If
        AllergiesDS.Update()
        DietaryDS.Update()
        SpecialNeedsDS.Update()
        ImpairmentDS.Update()
        DiagnosisDS.Update()
    End Sub

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