The linear regression equation for pressurised metered-dose inhaler: Using canister weight to predict balance actuation in asthma inhaler

Abstract INTRODUCTION Pressurised metered-dose inhalers (pMDIs) are not equipped with dose counters hence the balance actuation in a canister could not be determined. Each actuation expels a considerable amount of active ingredients and excipients from a canister, thus the balance actuation remaining in a pMDI based on canister weight could be evaluated using a linear regression equation.METHODOLOGY New pMDIs of 5 active ingredients [salbutamol (GSK) 200 actuation, budesonide (Glenmark) 300 actuation, ipratropium/fenoterol (Boehringer) 200 actuation, fluticasone (GSK/innovator) 120 actuation, fluticasone (Cipla/generic) 120 actuation, and beclometasone (Ivax) 200 actuation] was weighted . using a laboratory scale (Sartorius R200D; 0.01g accuracy). Two of each pMDI were weighed after each actuation, with a 30-second inter-puff interval, and the mean weight was recorded. To minimise variability in measurements, weighing was limited to one operator. The canister was considered empty when there were no changes in weight after repeated actuation. The prediction equation (one for each pMDI) was the line of best fit through data points on the scatter plot of the number of actuations versus weight.RESULTS AND DISCUSSION There was low variability between pMDIs weights (SD: 0.03g-0.08g)] of the same active ingredients indicating manufacturing uniformity among canisters. Prediction equations were generated for each type of active ingredients, where the general equation is: Actuation remaining = Constant + β*pMDI weight.CONCLUSION This study produced a prediction equation that can be used to estimate remaining actuation in a pMDI based on its weight. Weighing medication canister could be used to measure actuation remaining in pMDIs, as well as patients’ adherence to pMDIs.