Favorable combination effects of the leukotriene synthesis inhibitor BAY X 1005 and dexamethasone on edema formation in the arachidonic acid-induced mouse ear inflammation test

The effects of a combination of the leukotriene synthesis inhibitor (LSI) BAY X 1005 with the glucocorticosteroid dexamethasone were studied in the arachidonic acid (AA)-induced mouse ear inflammation test (AA-MEIT). We have determined the dose-dependent effects of dexamethasone to reduce edema formation when a combination of 25 mg/kg BAY X 1005 and increasing dosages of dexamethasone was administered orally (p.o.). The inhibition of ear thicknesses increases with the combination therapy were compared with the inhibition observed when both compounds were applied alone. The edema inhibition at the fixed oral dose of 25 mg/kg p.o. BAY X 1005 was 57+/-2%. Dexamethasone alone dose-dependently inhibited edema formation with a flat inhibition curve at dosages ranging from 0.008 mg/kg (11+/-13%) to 0.5 mg/kg (65+/-11%). In combination with BAY X 1005, the corresponding inhibition curve for dexamethasone was shifted upward starting from 56+/-13% at 0.008 mg/kg. At the two highest dexamethasone dosages (0.125 mg/kg and 0.5 mg/kg) an identical inhibition (86+/-10%) was observed indicating a plateauing of the antiedematous effect of this combination, The results indicate that at suitable dosages (0.031 mg/kg and 0.125 mg/kg) the effects of BAY X 1005 and dexamethasone were additive. To further corroborate the combination effects of BAY X 1005 and dexamethasone the 5-HT receptor antagonist methysergide and the H-1 receptor antagonist pyrilamine were employed as a pretreatment to eliminate mouse-specific inflammation responses. In the methysergide/pyrilamine (12.5 mg/kg s.c. each)-conditioned AA-MEIT model 85+/-3% edema reduction were observed with BAY X 1005 and 74+/-3% with dexamethasone. The combination of 25 mg/kg BAY X 1005 and 0.5 mg/kg dexamethasone was slightly more effective in the conditioned AA-MEIT (90+/-3%) than either compound alone. Our results demonstrate that the LSI BAY X 1005 interacted favorably with the glucocorticosteroid dexamethasone suggesting a potentially useful new combination strategy to treat acute inflammatory disease conditions. This effect can be explained on the basis of the mechanisms of action of both therapeutic principles.