The inhaler device efficiency is expected to influence inhaled corticosteroid therapeutic dose equivalence. Device efficiency (lung deposited dose/nominal dose) varies for dry-powder (DPI) and metered-dose (MDI) inhalers. The largest differences are seen between DPIs and chlorofluorocarbon (CFC) MDIs of low- to mid-range efficiency that emit particles mostly in the 3–5 µm range when compared with MDIs that contain drug dissolved in hydrofluoroalkane (HFA) propellant and generate an ultrafine aerosol plume with smaller particles (≈1 µm) and a greater proportion of the particles in the respirable range (<5 µm) [ 16 ]. The impact of device efficiency on therapeutic dose is explored in Figure 3 , which has on the y-axis the total daily dose estimated to be deposited in the lungs, obtained by correcting the nominal dose for the device efficiency. Figure 3 also includes data for DPIs and MDIs of both the CFC and higher-efficiency ultrafine aerosol HFA MDIs (FLU, BDP, CIC) (Table 1 ). Also included are low-, mid- and high-dose regimens of all currently available inhaled corticosteroids, illustrating for each dose level a distinct exponential decline in therapeutic daily dose with increasing potency. Therefore, one might expect that all dose regimens in the low-, mid- or high-dose categories, as defined by each regression line, should have equivalent efficacy. This may be the case, but is difficult to verify as the extent to which each product's recommended doses are based on comprehensive dose ranging in all severities of asthma is variable.
The aim of this article is to bring less well recognised adverse effects of inhaled corticosteroids to the attention of prescribers. Whilst inhaled steroids have a more favourable side effect profile than systemic steroids, they are not free from adverse effects. The dose of inhaled steroids used should be carefully monitored, and kept at the lowest dose necessary to maintain adequate control of the patient’s disease process. Be particularly aware of the cumulative effect of co-prescribing various dose forms of corticosteroids (inhaled, intranasal, oral and topical preparations).