Budesonide is an agonist of glucocorticoid receptors. It is used in the treatment of respiratory and digestive tract diseases by inhibiting inflammatory processes. For example, it inhibits the arachidonic acid cascade and the formation of inflammatory cytokines, which are critically involved in the development of inflammation.
Corticosteroids are generally bound to corticosteroid-binding globulin and serum albumin in plasma. Thus, overall plasma protein binding is approximately 85-90%. Budesonide is 80-90% metabolized at the first liver passage. Budesonide is metabolized by CYP3A4 to its 2 major metabolites, 6-beta-hydroxybudesonide and 16-alpha-hydroxyprednisolone. The activity of these metabolites is negligible (<1/100). Approximately 60% of a budesonide dose is excreted in the urine in the form of the major metabolites 6-beta-hydroxybudesonide and 16-alpha-hydroxyprednisolone. Budesonide has an elimination half-life of 2-4h.
With concomitant administration of digitalis glycosides, their effect may be enhanced. Saliuretics together with budesonide may lead to an increased excretion of calamine.
Particular care should be taken in combination with drugs which are also metabolised via the CYP3A4 enzyme. This can lead to increased plasma levels of the active substances and thus to increased side effects. Some drugs also increase the expression of CYP3A4, which may cause the plasma level of budenoside to fall below the effective concentration.
When taking steroid-binding resins such as colestyramine, plasma levels of budenoside may also fall below the effective concentration.