In vitro activity: Loratadine is identified as a selective inhibitor of B(0)AT2 with an IC50 of 4 μM while being less active or inactive against several other members of the SLC6 family. Loratadine concentration-dependently inhibits the release of histamine and LTC4 when preincubating before Der p 1 antigen or anti-Fc epsilon RI challenge in human Fc epsilon RI+ cells. Loratadine (0.1 mM) also inhibits (10-40%) histamine, LTC4, and PGD2 release from purified HLMC (16-68%) activated by anti-Fc epsilon RI. Loratadine causes concentration-dependent inhibition (10-40%) of histamine, tryptase, LTC4, and PGD2 release from purified HSMC (24-72%) immunologically challenged with anti-Fc epsilon RI. Loratadine inhibits significantly IL-6 and IL-8 secretion induced by histamine with a more powerful efficiency of the active metabolite in human umbilical vein endothelial cells (HUVEC). Loratadine blocks hKv1.5 channels in a concentration-, voltage-, time- and use-dependent manner but only at concentrations much higher than therapeutic plasma levels in man in Ltk- cells transfected with the gene encoding hKv1.5 channels. Loratadine inhibits rhinovirus-induced ICAM-1 upregulation in both primary bronchial or transformed (A549) respiratory epithelial cells. Loratadine also inhibits ICAM-1 mRNA induction caused by rhinovirus infection in a dose-dependent manner, and they completely inhibits rhinovirus-induced ICAM-1 promoter activation.

Cell Assay: Loratadine(SCH-29851) is a selective inverse peripheral histamine H1-receptor agonist with an IC50 of>32 μM. Loratadine is a non-sedative antihistamine that inhibits histamine-induced activities of IL-6 and IL-8 secretion in endothelial cells.