How to select a value from CSV in an asp.net ajax toolbox autocomplete and pass that value to other textboxes?

I have used Ajax toolkit autocomplete working fine using the following asp.net and C# code.<asp:UpdatePanel ID="updPnlMedicineName" runat="server" ><ContentTemplate> Name<br /><asp:TextBox ID="txtMedName" runat="server" Width="150px" ontextchanged="txtMedName_TextChanged"></TextBox><cc1:AutoCompleteExtender ID="txtSearchID_AutoCompleteExtender" runat="server"
DelimiterCharacters="" OnClientItemSelected="ItemSelected" Enabled="True" GetMedicine"
 ServicePath="Search/NameSearch.asmx" TargetControlID="txtMedName" MinimumPrefixLength="1"></cc1:AutoCompleteExtender>

My code Behind is :

[WebMethod]
public string[] GetMedicine(string prefixText)
{
 List<string> listString = new List<string>();
 using (SqlConnection con = new  SqlConnection(ConfigurationManager.ConnectionStrings["NewLandConnectionString"].ConnectionString))
{
 SqlCommand com = new SqlCommand("select ProductName+','+ProductCode+',' + (select unitName from Unit where Unit.Id=product1.UnitId) as ProductDetails,ProductId from product1 where ProductName like '"+prefixText+"%'", con);
 con.Open();
 SqlDataAdapter adr = new SqlDataAdapter(com);
 DataTable dt = new DataTable();
 adr.Fill(dt);
  for (int j = 0; j < dt.Rows.Count; j++)
        {
            string countProduct = dt.Rows[j]["ProductDetails"].ToString();

           listString.Add(AutoCompleteExtender.CreateAutoCompleteItem(dt.Rows[j]["ProductDetails"].ToString(),dt.Rows[j]["ProductId"].ToString()));
        }
  }
    string[] strarray = listString.ToArray();
    return strarray;
 }

Now when my auto complete works i get values in the form of : somename,code,unit but i want that if a value is selected then i must get only the first value from csv i.e "somename" in that texbox and other two values(i.e code,unit ) must be populated in other texboxes respectively.

Please, help me in achieving this task.

Thanks in advance !!