Tepoxalin (RWJ 20485) is a 5-lipoxygenase inhibitor potentially for the treatment of asthma, osteoarthritis. Tepoxalin inhibits COX-1, COX-2, and 5-LOX. Tepoxalin is a potent inhibitor of sheep seminal vesicle cyclooxygenase (COX) (IC50 = 4.6 microM), rat basophilic leukemia cell (RBL-1) lysate COX (IC50 = 2.85 microM) and COX from intact RBL-1 cells (IC50 = 4.2 microM).

Tepoxalin inhibits the production of thromboxane B2 (TxB2) in Ca++ ionophore A-23187-stimulated human peripheral blood leukocytes (HPBL; IC50 = 0.01 microM) and human whole blood (IC50 = 0.08 microM) and is a potent inhibitor of epinephrine-induced human platelet aggregation (IC50 = 0.045 microM). Tepoxalin inhibits lipoxygenase (LOX) in RBL-1 lysates (IC50 = 0.15 microM) and intact RBL-1 cells (IC50 = 1.7 microM) and inhibits the generation of leukotriene B4 (LTB4) in calcium ionophore A-23187-stimulated HPBL (IC50 = 0.07 microM) and human whole blood (IC50 = 1.57 microM). Human platelet 12-LOX (IC50 = 3.0 microM) is inhibited, but 15-LOX is only weakly so (IC50 = 157 microM)[3].

Tepoxalin inhibits inflammation and microvascular dysfunction induced by abdominal irradiation in rats.[1]In vivo, tepoxalin, administered orally, demonstrated potent anti-inflammatory activity in the established adjuvant arthritic rat (ED50 = 3.5 mg/kg) and potent analgesic activity in the acetic acid abdominal construction assay in mice (ED50 = 0.45 mg/kg). In an ex vivo whole blood eicosanoid production assay, tepoxalin produces a dose-related inhibition of prostaglandin (PG) and LT production in dogs (PGF2 alpha - ED50 = 0.015 mg/kg; LTB4 - ED50 = 2.37 mg/kg) and adjuvant arthritic rats following oral administration. In adjuvant arthritic rats, tepoxalin is devoid of ulcerogenic activity within its anti-inflammatory therapeutic range (1-33 mg/kg p.o.) and does not exhibit ulcerogenic activity in normal rats at doses lower than 100 mg/kg (UD50 = 173 mg/kg p.o.)[3].