Variation of peak inspiratory flow through dry powder inhalers in children with stable and unstable asthma.

Drug release from dry powder inhalers depends for a large part on a sufficiently high peak inspiratory flow (PIF). We determined the variation of PIF through two commonly prescribed dry powder inhalers in children with asthma. We analyzed the effect of inhaler device, age, and severity of asthma symptoms on variation of PIF. Fifty-eight children with asthma (4-15 years old) recorded PIF values together with asthma symptoms in a diary twice daily for 4 weeks. PIF was measured with a portable PIF-meter (In-Check) equipped with adapters to simulate flow resistance through the Accuhaler and Turbohaler inhalers. Children generated higher PIF values through an Accuhaler adapter than through a Turbohaler adapter (95% CI for difference, 25.7-31.7). Mean PIF values increased with age, independent of type of inhaler. The mean (SD) variation of PIF (low%high) was 72.3 (8.1)% for patients using the Accuhaler adapter, and 67.0 (14.5)% for patients using the Turbohaler adapter (mean difference, 5.2%; 95% CI, -0.9 to 11.4). Children < or =7 years of age had a significantly greater variation of PIF in addition to a lower mean PIF (P = 0.0003). PIF decreased significantly when symptoms of asthma increased (mean maximal decrease 11 l/min; P < 0.01), but the correlation between PIF and morning and evening symptoms was weak (r = -0.18 and r = -0.16, respectively). Patients who reported moderate or severe symptoms during the study period had a significantly greater variation of PIF compared to patients who remained free of symptoms or reported mild symptoms. The majority of patients generated PIF >30 l/min during the study, even when they experienced symptoms of asthma. The variation of PIF through the Accuhaler and Turbohaler adapter was significantly greater for children < or =7 years of age and for patients experiencing moderate or severe symptoms of asthma.