Introduction and objective Salbutamol pMDIs in the UK do not include dose-counters. Di Paolo¹ determined that Ventolin Evohalers can be weighed to determine how much medication remains; as the 200 doses are used, the canister’s weight falls from 29 g to 15 g. We investigated if patients discard inhalers still containing medication, or continue to use empty pMDIs which could contribute to worsening clinical condition.

Method Fifty Ventolin Evohalers from hospital inpatients were weighed using digital scales to determine the number of doses left. Data were also collected regarding how many doses patients believed were remaining and how they determine when their inhaler is empty. One new inhaler was used as a ‘full’ control, and another was emptied to use as an ‘empty’ control.

Results Our calibration was consistent with Di Paolo⁽¹⁾. However, we found an inhaler weighing 15 g still rattles and will continue to emit a visible spray for approximately another 100 puffs until the weight reaches 11 g. Fifty inhalers were examined from 48 patients with mean age 71 years. Six patients (12%) were unknowingly using inhalers weighing less than 15 g; four of these six were admitted for exacerbations of airways disease. Most patients (66%) underestimated the number of remaining doses. 23 patients (46%) reported that they consider their inhaler empty ‘when nothing comes out’ and 13 patients (26%) use the ‘shake method’. The linear regression in figure 1 shows, on average, patients perceive their inhaler to be empty when 82 doses remain.

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Abstract P169 Figure 1

Perceived vs actual doses remaining in inpatients’ Ventolin pMDIs

Conclusions Hospital inpatients use ineffective methods to determine how many doses remain in Ventolin Evohalers, with most patients underestimating the number of remaining doses. 12% use more than 200 actuations, potentially getting sub-therapeutic doses. Our analysis suggests patients perceive their inhaler to be empty when 82 doses remain. This correlates with recycling data, showing that on average 96 doses remain in discarded pMDIs. Prescribers should consider switching to salbutamol dry-powder inhalers which have dose-counters, could reduce waste and greenhouse gas emissions, prevent on-going use of empty inhalers and may be more cost-effective.

Reference

1. Di Paolo, et al. Stop using the flotation technique and start weighing salbutamol pressurised metered-dose inhalers without dose-counters. SwissMedWkly2015;145:w14162.