OBJECTIVETo compare the bronchofilating and antiallergic effects with piclamilast with ciclamilast, the second-generation phosphodiesterase 4 (PDE4) selective inhibitors.

METHODSEffects of piclamilast and ciclamilast on airway smooth muscle (ASM) at resting tension, carbachol-induced contraction and the synergistic effect of two agents on isoproterenol-induced bronchorelaxation were evaluated in the isolated tracheal strips of guinea pig in a cumulative manner in vitro. Slow reaction substance of anaphylaxis (SRS-A) release from lung tissues of the sensitized guinea pigs after antigen challenge was examined by bioassay. Antiallergic effect of piclamilast, ciclamilast and rolipram on the isolated ASM of sensitized guinea pigs were evaluated with Schultz-Dale reaction.

RESULTSPiclamilast and ciclamilast showed bronchorelaxant effect in ASM at resting tension. EC50 values of piclamilast and ciclamilast were 1.00 x 10(-5) mol/L and 0.84 x 10(-5) mol/L. Piclamilast and ciclamilast could both enhance the bronchodilating effect of isoproterenol in the isolated ASM of guinea pig, reduce the amount of SRS-A released from lung tissues of the sensitized guinea pigs and also inhibit ovalbumin (OA)-induced bronchoconstruction (Schultz-Dale reaction).

CONCLUSIONThe results indicate the bronchodilating effect of ciclamilast is as potent as piclamilast, but the antiallergic effect of ciclamilast is significantly more potent than that of piclamilast.