The effect of shaking on solution MDIs

Researchers at Schering Plough, now Merck, undertook a study of factors that influence the delivered dose of suspension MDIs. Theoretically, suspension MDIs require shaking in order to break up flocculates and distribute the drug homogeneously during the filling of the inhaler’s valve chamber, and failure to shake the device adequately could result in inconsistent dosing [3]. In order to provide a control for the shaking study, the researchers included a solution MDI, whose performance, theoretically, should be independent of shaking since drugs in solution are naturally homogenous. Surprisingly, however, both total shot weight and drug delivery for the solution MDI showed a strong dependence on the vigorousness of shaking prior to actuation, indicating that shaking plays a role in valve performance and suggesting that developers of MDIs may need to account for shaking and actuation factors regardless of the type of formulation.