PubMed · 8376102
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D H Upmalis. Stadol NS.. https://doi.org/10.1111/j.1526-4610.1993.hed3307394.x
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In vitro analysis of inhaled formulations measures, among other parameters, the variability in delivered dose, while a corresponding in vivo analysis also includes the variability caused by patient performance and distribution of drug between the oropharynx and the lungs. In vitro, the dose variability is higher for Turbuhaler(R) than for the corresponding pMDI, whereas in vivo, the converse is true: the variability in lung deposition is significantly higher, both between and within subjects, for pMDI than for Turbuhaler. The observation can be due to several factors such as the non-continuous working principle of inhalation via pMDI as opposed to the continuous working principle of inhalation via Turbuhaler.
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The aim of this study was to evaluate the effect of instructions to children with asthma (given by general practitioners or by pharmacy assistants) on how to inhale from metered dose inhalers with spacers (MDI/s) or dry powder inhalers (DPI). We scored inhalation technique of asthmatic children according to criteria defined by the Netherlands Asthma Foundation, and related the performance to the inhalation instructions given. For each inhaler, a number of steps were considered essential for reliable drug delivery. Patients newly referred for asthma were asked to demonstrate their inhalation technique and to fill out a questionnaire on the inhalation instruction received prior to referral. Children participating in a clinical trial, who had received repeated comprehensive inhalation instructions, served as a control group. Sixty-six newly referred patients (1-14 years of age, median age 5 years; 37 boys) and 29 control patients (5-10 years of age, median age 7 years; 21 boys) completed the study. Sixty patients (91%) had received inhalation instruction prior to referral. Only 29% of these patients, using a dry powder inhaler, performed all essential steps correctly, compared to 67% of children using a metered dose inhaler/spacer combination (P < 0.01). Children who had received comprehensive inhalation instructions with repeated checks of proper inhalation technique at the pharmacy or in the clinical trial setting were more likely to perform all essential steps correctly (79% and 93%, respectively) than children who had received a single instruction by a general practitioner (39%, P < 0.01). Many asthmatic children use their inhalers devices too poorly to result in reliable drug delivery, even after inhalation instruction. Comprehensive inhalation instruction and repeated check-ups are needed to assure reliable inhalation technique.