Olopatadine hydrochloride

Olopatadine hydrochloride (Opatanol) is a histamine blocker and mast cell stabilizer with an IC50 of 559 uM for the release of histamine. Evaluation of the interaction of olopatadine with histamine receptors revealed a relatively high affinity for the H1 receptor (Ki = 31.6 nM, pKi = 7.5 ?0.1) but lower affinities for H2 receptors (Ki = 100 uM, pKi = 4.0 ?0.19) and H3 receptors (Ki = 79.4 uM, pKi = 4.1 ?0.16,). The H1 selectivity of olopatadine was superior to that of other ocularly used anti-histamines studied, such as ketotifen, levocabastine, antazoline and pheniramine.