Background: Inhaled corticosteroid (ICS) will be effective if used properly. Inadequate intake may result in insufficiency, such as for elderly asthmatics, in particular, for use of dry powder inhalers. Methods: 312 asthmatics treated with ICS for at least 6 months in the 6 facilities belonging to the Chugoku Shikoku Adult Asthma Research Forum were subject to investigation of the peak inspiratory flow (PIF) measured using In-check® and related factors. Results: Nine (2.8%) patients were considered to have insufficient intake. By multivariate analysis, PIF (L/min) prediction formula was as follows: 79.0 + 0.19*peak expiratory flow (PEF: L/min) + 22.9*FVC (L) - 0.68*onset age (years) + 34.7*gender (male, 1
female, 0) + 16.1*V50/V25, [r∧2 = 0.677, p&lt
0.0001]. Using cluster analysis with Euclidean distance and Ward's method, the PIF without an adaptor was included in the same category as height and PEF, and the PIF with an adaptor was included in the same category as %FVC and %FEV 10. Conclusion: The cases with insufficient PIF are few but present. Adequate device selection and inhalation guidance may be important. The meaning of PIF differs depending on whether or not an adaptor is present. Further investigation of intake is considered necessary. ©2011 Japanese Society of Allergology.