Background Most patients using pressurised metered dose inhalers (pMDIs) without a built-in dose counter often arbitrarily gauge the doses left in the canister using imprecise methods. As the delivered dose becomes variable beyond the labelled maximum dose for pMDIs, this imprecise practice may lead to patients receiving sub-therapeutic doses and putting their lives at risk, especially for reliever medication. Sub-therapeutic doses of controller medication may adversely affect asthma control. In some situations, patients may be discarding their pMDIs too early.

Objectives We propose a simple and cost-effective method to ensure safe use of pMDIs without a built-in dose counter.

Methods We created customised adhesive count stickers with running numbers up to the maximum dose for various pMDIs that can be pasted on the inhalers. Patients would struck off a number after the administration of a dose on the sticker, and were therefore able to keep track of the doses left on the pMDI. They were instructed to change to a new pMDI once the numbers on the count stickers were fully struck off. We compared the weight of the empty/used pMDIs collected from patients before and after the introduction of adhesive count stickers, to objectively assess if patients were changing to new inhalers too early or too late, and determine the effectiveness of the adhesive count stickers.

Results A total of 200 empty/used pMDIs were collected from patients both pre-intervention and post-intervention. Our results showed statistical significant differences in the weight of the canisters collected prior to and after the intervention. The median weight of the salbutamol pMDIs collected from patients pre-intervention was 9.495 g and post-intervention was 11.075 g. The median weight of the fluticasone diproprionate pMDIs collected from patients pre-intervention was 9.745 g and post-intervention was 12.145 g. There is statistically significant safety margin of 1.58 g and 2.40 g for each category of pMDI respectively. The adhesive count stickers were well received by the patients with good feedback.

Conclusions Our results suggest that without objective methods of dose counting, patients are using their pMDIs beyond the labelled maximum dose and replacing with new inhalers too late for both reliever and controller medications. This is of clinical concern. The use of adhesive count stickers can help patients keep track of remaining doses objectively in a simple manner, with a good safety margin shown above. The use of the medication in the pMDIs can also be maximised with minimal wastage.