Selecting the Optimal Inhaler in Asthma: Respiratory and Peripheral Muscle Strength as Predictors of DPI and MDI Response

Background: Asthma is characterized by variable airway obstruction, and proper inhaler choice and use are critical for effective treatment. This study aimed to identify factors influencing treatment response in newly diagnosed patients started on dry powder inhalers (DPIs) or metered-dose inhalers (MDIs). Methods: Between March and September 2025, 177 newly diagnosed asthma patients were screened. Eighty patients with at least high-school education, correct inhaler use, and good adherence were included (40 DPI, 40 MDI). Pulmonary function, respiratory muscle strength, Asthma Control Test (ACT), and handgrip strength (HGS) were assessed at baseline and after one month. Results: After one month, improvements in forced expiratory volume in 1 second (FEV 1 ) (% predicted), maximum inspiratory pressure (MIP) and MIP (%), and maximum expiratory pressure (MEP) (%) were significantly greater in the DPI group compared with the MDI group ( p = 0.03, 0.04, 0.02 respectively). In multivariate regression, among MDI users, MIP (kPa) ( B = −11.305, p = 0.001), MIP (%) ( B = −0.902, p = 0.003), ACT ( B = 1.277, p = 0.014), and HGS ( B = 0.103, p = 0.039) were independent predictors of ΔFEV 1 (%). Among DPI users, MIP (kPa) ( B = 11.987, p = 0.015), MIP (%) ( B = 1.041, p = 0.009), MEP (kPa) ( B = −6.554, p = 0.014), MEP (%) ( B = −0.816, p < 0.001), and HGS ( B = 0.201, p = 0.005) were significant determinants of ΔFEV 1 . Conclusion: DPIs may be preferable for patients with higher inspiratory muscle strength, whereas MDIs may be better for those with lower MIP. HGS appears to be an important factor for both inhaler control and treatment efficacy.