Pharmacokinetics and pharmacodynamics of inhaled corticosteroids.

There are significant differences in the pharmacokinetic properties of inhaled corticosteroids currently used in medical practice. All are rapidly cleared from the body but they show varying levels of oral bioavailability and more importantly variation in the rate of absorption after inhalation. Oral bioavailability is lowest for fluticasone propionate, indicating a low potential for unwanted systemic corticosteroid effects. Mathematical modeling has shown pulmonary residence times to be longest for fluticasone propionate and triamcinolone acetonide but shortest for budesonide and flunisolide. These properties appear to relate to pulmonary solubility, which appears to be the rate-limiting step in the absorption process.