So, they will need to do more work to find a compound with higher activity to be useful in humans, so us Lyme disease sufferers will have to wait. Nevertheless, it is a very interesting finding. The problem is that the authors state that the in vitro concentration required for activity of desloratadine against Lyme spirochetes is 78 µg/mL which is the same as 78 mg/L. A human has about 5 L of blood, so even if an entire dose stayed in the bloodstream, which is unlikely, close to 400 mg would be required, which is ~80 times the recommended daily dose of desloratadine, which would cause severe and possibly fatal side effects.

The authors' original research paper is available as a PDF:

http://www.dovepress.com/getfile.php?fileID=23671