1. Introduction
Triptolide, which possesses potent anti-inflammatory and immunosuppressive properties, is one of the major active components in the Chinese herbal remedy Tripterygium wilfordii Hook F (TWHF) 1, 2, 3 and 4. Triptolide has been reported to be therapeutically efficacious in the treatment of rheumatoid arthritis (RA) 5, 6 and 7, but the strong toxicity of triptolide towards the gastrointestinal, hepatic, renal and reproductive systems has restricted its oral application to a great extent 8 and 9. Triptolide also has a narrow therapeutic window, with an effective dose is nearly equal to its toxic dose 10. To overcome these disadvantages, chemical modification and biotransformation of triptolide has been investigated 11, 12 and 13. In addition, transformation of the dosage form has also been explored 14 and 15, and a transdermal drug delivery preparation of triptolide, using a triptolide-loaded microemulsion has been developed by our laboratory 16