Abstract: Objective To Investigate the effects of antipsoriatic drugs on 5.lipoxygenase(5-LO) and set up a relevant pharmacodynamic method. Methods 5-LO products, leukotriene B4 (LTB4) and 5.hydroxyeicosatetraenoic(5-HETE), we re determined by RP-HPLC to represent 5-LO activity. Results Cyclosporin A(CyA) and triptolide(T₀) inhibited the production of LTB4 and 5-HETE in a dose-dependent manner, while erythromycin did without dose.dependence. The 50% inhibitory concentration values(IC₅₀) of CyA inhibiting LTB4 and 5-HETE were 38.0μg/mL and 0.96μg/mL, respectively. The IC₅₀ of T₀ inhibiting LTB4 and 5-HETE were 2.3×10^-6μg/mL and 1.14×10^-6μg/mL, respectively. Conclusions The anti.inflammatory effect of Tripterygium wilfordii Hook.f. may be partly explained by its inhibition of 5-LO activity. The anti.inflammatory effect of CyA has no clinical significance since the inhibitory concentration of CyA has exceeded its pharmacological limitation. Erythromycin has no effect on 5-LO activity.

Key words: Arachidonic acid, 5-lipoxygenase, Leukotriene B4, Hydroxyeicosatet raenoic acids, Cyclosporin, Triptolide, Erythromycin