Boston-Ophthalmic solutions of azelastine HCl (Optivar, Asta Medica/Muro Pharmaceutical Inc., Tewksbury, MA) and olopatadine HCl (Patanol, Alcon Laboratories, Fort Worth, TX) both effectively inhibit the activation of normal cultured human mast cells and the release of interleukin-6 (IL-6), tryptase, and histamine. However, azelastine seemed to be substantially more potent for treating ocular allergy when the two drugs were compared in an in vitro study.