Ciclesonide(RPR251526) is a glucocorticoid used to treat obstructive airway diseases. Target: Glucocorticoid Receptor Ciclesonide (CIC) is an inhaled glucocorticosteroid. CIC (5 microM) was rapidly hydrolyzed by NHBE cells (approximately 30% conversion at 4h), with almost complete conversion by 24h. In liver and NHBE cells, major involvement of cytosolic carboxylesterases, with some contribution by cholinesterases, was indicated. The highest level of conversion was found in the liver, the site of inactivation of des-CIC through rapid oxidation by cytochrome P450. Carboxylesterases in bronchial epithelial cells probably contribute significantly to the conversion to des-CIC in the target organ, whereas low systemic levels of des-CIC are a result of the high metabolic clearance by the liver following CIC inhalation [1]. Ciclesonide may have some advantage although it is not as yet licensed in all countries for paediatric use [2].