(±)-Tazifylline is a selective and long-acting antagonist of histamine H1 receptor. Tazifylline shows much lower affinity for H2 receptors, α- and β-adrenoceptors, 5-hydroxytryptamine and muscarinic receptor subtypes.

Tazifylline potently inhibits contractions evoked by stimulation of histamine H1-receptors in isolated guinea pig ilea and exhibits high affinity in radioligand binding studies[1].

In anesthetized guinea pigs, Tazifylline causes an inhibition in histamine-induced bronchoconstriction and protects conscious animals from the lethal effect of large doses of the amine. In conscious rats, Tazifylline reduces the inflammatory effects of intradermal histamine. In conscious dogs, Tazifylline(orally) causes inhibition in histamine-induced skin inflammation for long periods of time, and in anesthetized animals attenuated that portion of the histamine-evoked hypotension attributable to stimulation of H1 receptors. Large oral doses of Tazifylline do not reduce spontaneous locomotor activity in mice, nor do they produce overt symptoms of behavioral depression in conscious rats[1].