Studies with oral and intravenous dosing of radiolabeled ciclesonide have shown an incomplete extent of oral absorption (%). The oral bioavailability of both ciclesonide and the active metabolite is negligible (<% for ciclesonide, <1% for the metabolite). Based on a γ-scintigraphy experiment, lung deposition in healthy subjects is 52%. In line with this figure, the systemic bioavailability for the active metabolite is >50% by using the ciclesonide metered dose inhaler. As the oral bioavailability for the active metabolite is <1%, the swallowed portion of the inhaled ciclesonide does not contribute to systemic absorption.
One of the most crucial components of a MDI is its propellant. The propellant provides the force to generate the aerosol cloud and is also the medium in which the active component must be suspended or dissolved. Propellants in MDIs typically make up more than 99% of the delivered dose,  so it is the properties of the propellant that dominate more than any other individual factor. This is often overlooked in literature and in industry because so few propellants are used and their contribution is often taken for granted. Suitable propellants must pass a stringent set of criteria, they must: