Unbound corticosteroids cross cell membranes and bind with high affinity to specific cytoplasmic receptors. Inflammation is decreased by diminishing the release of leukocytic acid hydrolases, prevention of macrophage accumulation at inflamed sites, interference with leukocyte adhesion to the capillary wall, reduction of capillary membrane permeability, reduction of complement components, inhibition of histamine and kinin release, and interference with the formation of scar tissue. The antiinflammatory actions of corticosteroids are thought to involve phospholipase A2 inhibitory proteins, lipocortins, which control the biosynthesis of potent mediators of inflammation such as prostaglandins and leukotrienes. Mometasone furoate has been shown in vitro to exhibit a binding affinity for the human glucocorticoid receptor which is approximately 12 times that of dexamethasone, 7 times that of triamcinolone acetonide, 5 times that of budesonide, and 1.5 times that of fluticasone.
Mometasone is a medium-potency synthetic corticosteroid with antiinflammatory, antipruritic, and vasoconstrictive properties. Studies in asthmatic patients have demonstrated that mometasone provides a favorable ratio of topical to systemic activity due to its primary local effect along with the extensive hepatic metabolism and the lack of active metabolites. Though effective for the treatment of asthma, glucocorticoids do not affect asthma symptoms immediately. Maximum improvement in symptoms following inhaled administration of mometasone furoate may not be achieved for 1 to 2 weeks or longer after starting treatment. When glucocorticoids are discontinued, asthma stability may persist for several days or longer. Mometasone has been shown in vitro to exhibit a binding affinity for the human glucocorticoid receptor which is approximately 12 times that of dexamethasone, 7 times that of triamcinolone acetonide, 5 times that of budesonide, and 1.5 times that of fluticasone. The clinical significance of these findings is unknown.
Hepatic. Extensive metabolism to multiple metabolites. There are no major metabolites detectable in plasma. Upon in vitro incubation, one of the minor metabolites formed is 6ß-hydroxy-mometasone furoate. In human liver microsomes, the formation of the metabolite is regulated by cytochrome P-450 3A4.
The potential for acute toxic effects following overdose with the mometasone inhaler is low. However, habitual overuse of the product can cause symptoms of steroid overload, including menstrual irregularities, acne, obesity, and muscle weakness. Single oral doses up to 8000 µg have been studied on human volunteers with no adverse events reported.