Multiple actuations of salbutamol MDI into a spacer device reduce the amount of drug recovered in the respirable range

Abstract

We wanted to determine the amount of salbutamol available in respirable particles from the Volumatic spacer device after one, two or five actuations of a metered-dose inhaler into the spacer prior to analysis.A glass multistage liquid impinger was used to determine particle size. Aerosol was sampled after one, two or five actuations from a metered-dose inhaler into a Volumatic spacer. Each experiment was repeated four times.The amount of salbutamol recovered per actuation in particles less than 5 µm (mean and 95% confidence intervals) was: 54.3 µg (48.3-60.1) after one actuation; 42.4 µg (38.2-46.5) after two actuations, and 20.7 µg (17.5-23.9) after five actuations.We conclude that multiple actuations of salbutamol into the Volumatic spacer do not linearly increase the amount of drug available for inhalation. To maximize drug delivery, single actuations should be used prior to inhalation. In comparative studies of drugs and dosages, it must be remembered that the amount of drug delivered is not the same as that administered. Eur Respir J., 1994Respir J., , 7, 1707 by drawing an aerosol through a series of stages, each containing a glass impaction plate. Aerosol velocity increases in the device and progressively smaller particles collect at each stage. A filter after the final stage collects the smallest particles. Each stage was washed with methanol, and the amount of drug collected in each stage was assayed by high performance liquid chromatography with an ultra-violet detector at a wavelength of 276 nm.A standard MDI of salbutamol (Allen & Hanburys, 100 µg per actuation) was shaken for 10 s, connected to the MSLI and discharged into it. This was repeated 10 times to facilitate the drug assay.The experiment was repeated using the Volumatic spacer. The MDI was shaken and then actuated into the spacer. This was immediately attached to the MSLI. The spacer was positioned so that drug would not be drawn into the MSLI before attachment. To assess the effect of multiple actuations into the spacer, the MDI was actuated into the spacer one, two or five times prior to attaching it to the MSLI. For each of the experiments, the aerosol was actuated a total of 10 times. Before each actuation, the MDI was shaken for 10 s. Five new metered-dose inhalers were used. The first 10 doses from each were discarded, and the metered dose-inhaler primed by firing one shot to waste prior to each experiment.Each experiment was repeated four times, and the temperature, relative humidity and barometric pressure were recorded. The size distribution of the aerosol cloud was In the delivery of drugs to the respiratory tract, spacer devices are used to reduce the need to co-ordinate inhalation and metered-dose inhaler (MDI) actuation. Optimum spacer use improves asthma management and reduces the waste of drugs, which result from poor inhaler technique [1].Factors which affect the amount of drug obtained from spacers are not widely appreciated. Recent guidelines for the management of acute severe asthma recommend the administra...

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