Pharmacokinetic optimisation of inhaled steroid therapy in asthma.

The recognition that asthma has a large inflammatory component has led to the use of steroids in its treatment. The adverse systemic effects of the drugs have promoted the development of inhaled steroids with a high topical to systemic potency ratio. The 2 most widely used agents are beclomethasone dipropionate and budesonide. Budesonide has a longer plasma elimination half-life than beclomethasone dipropionate but a higher topical to systemic potency ratio. These agents have been shown to be equipotent with respect to their anti-asthma effects but budesonide may have a slightly more favourable adverse effect profile. At low dosages (up to 400 micrograms/day) these drugs are well tolerated. At higher dosages (> 1000 micrograms/day) adverse effects on bone metabolism and adrenal function have been noted. Other agents such a triamcinolone or flunisolide have no obvious advantages. We recommend that inhaled steroids should be prescribed at the lowest dose required to control symptoms, with the dose being increased or decreased in a stepwise manner in parallel with asthma severity.