Run a command via cmd

I'm trying to run cmd.exe with admin privilege and use flushdns on it, how can i do it though ? and catch the output to a TMemo, the attached code is what i'm using but it doesn't seem to flush the DNS cache, where do i put "/flushdhsn" in ?

procedure RunDosInMemo( DosApp: String; AMemo: TMemo ) ;
const
  ReadBuffer = 2400;
var
  Security : TSecurityAttributes;
  ReadPipe, WritePipe : THandle;
  si : TStartUpInfo;
  pi : TProcessInformation;
  Buffer : PAnsiChar;
  BytesRead : DWord;
  Apprunning : DWord;
begin
  With Security do
   begin
    nlength := SizeOf(TSecurityAttributes) ;
    binherithandle := true;
    lpsecuritydescriptor := nil;
   end;
  if Createpipe(ReadPipe, WritePipe, @Security, 0) then
   begin
    Buffer := AllocMem(ReadBuffer + 1);
    FillChar( si, Sizeof(si), #0 );
    si.cb := SizeOf( si );
    si.hStdOutput := WritePipe;
    si.hStdInput := ReadPipe;
    si.dwFlags := STARTF_USESTDHANDLES + STARTF_USESHOWWINDOW;
    si.wShowWindow := SW_HIDE;

    if CreateProcess( PChar(DosApp), '-flushdns', @Security, @Security,
                            TRUE, NORMAL_PRIORITY_CLASS, nil, nil, si, pi)
    then
    begin
     repeat
      Apprunning := WaitForSingleObject( pi.hProcess, 100 );
      Application.ProcessMessages;
     until (Apprunning <> WAIT_TIMEOUT);
      Repeat
        BytesRead := 0;
        ReadFile(ReadPipe, Buffer[0], ReadBuffer, BytesRead, nil);
        Buffer[BytesRead] := #0;
        OemToAnsi( Buffer, Buffer );
        AMemo.Text := AMemo.Text + String(Buffer) ;
         Application.ProcessMessages;
      until (BytesRead < ReadBuffer);
   end;
   FreeMem( Buffer ) ;
   CloseHandle( pi.hProcess ) ;
   CloseHandle( pi.hThread ) ;
   CloseHandle( ReadPipe ) ;
   CloseHandle( WritePipe ) ;
   end;
end;

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