Patients do not take prescribed doses

EDITOR—The conclusions reached by Pethica et al in their paper concerning the relative potency of inhaled beclomethasone and budesonide are not justified because the authors have not verified an important assumption in the paper.1 They have assumed that patients are regularly taking the dose recorded on their prescription; the data presented in their paper suggest that this is most unlikely. The total number of prescriptions issued to 5930 patients was only 16 725 (under three a year). Most formulations of inhaled steroid last 50 days at the usual prescribed dose, so patients taking regular treatment should have used around seven prescriptions in the 12 months of the study.

Analysis of computerised prescriptions in my practice over the 12 months July 1997 to June 1998 shows a similar pattern: 625 patients received 2424 prescriptions for inhaled steroids (around four a year on average). Analysis of individual data on 59 patients aged 30-35 shows that 36 of the 59 were prescribed fewer than four inhalers a year (table). These patients did not receive enough medication to have taken the prescribed dose of inhaled steroid regularly over the 12 months.

The analysis carried out in Pethica et al's paper is based on the mean prescribed dose, which may bear little relation to the dose actually taken over the whole period. The total inhaled dose for each patient would be better estimated by multiplying the contents of each inhaler by the number of inhalers prescribed over the 12 months studied. Analysis should be restricted to those patients who can be shown to be taking regular inhaled steroids.

Beclomethasone is available as a 100 μg metered dose inhaler, while budesonide is available for adults only as a 200 …