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

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 microns (mean and 95% confidence intervals) was: 54.3 micrograms (48.3-60.1) after one actuation; 42.4 micrograms (38.2-46.5) after two actuations, and 20.7 micrograms (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.