Betamethasone 21-phosphate is a synthetic glucocorticoid.1It prevents increases in macrophage and eosinophil numbers in bronchoalveolar lavage fluid (BALF) and decreases in blood leukocyte numbers in a guinea pig model of parainfluenza-3 viral infection when administered at a dose of 8 mg/kg but does not prevent airway hyperresponsiveness after infection.2Betamethasone 21-phosphate inhibits cell infiltration into the aqueous humor in a rat model of endotoxin-induced uveitis when administered topically or subcutaneously at doses of 0.01-1% or 1 mg/kg, respectively.3It increases maximal lung pressure volume curves in fetal sheep when administered to pregnant ewes at 0.75 gestation at doses of 80 and 170 μg/kg.1Betamethasone 21-phosphate increases body weight, impairs learning and memory, increases anxiolytic behavior, and reduces hippocampal neurogenesis in CD-1 mice but reduces body weight and increases neurogenesis with no effect on anxiety in high-anxiety DBA/2 mice when administered at a dose of approximately 25 mg/kg per day in the drinking water for seven weeks.4Formulations containing betamethasone 12-phosphate and betamethasone acetate have been used in the treatment of severe allergic conditions and a variety of immune-related conditions.