This invention relates to a solution formulation comprising a tiotropium salt, 12-20% ethanol, 0.1-1.5% of water, 0.05-0.10% citric acid (or other organic acid) and an HFA propellant, wherein the percentages are percentages by weight based on the total weight of the formulation. The invention also provides a pMDI comprising a canister containing the formulation.本發明係關於一種溶液調配物,其包含噻托銨鹽、12-20%乙醇、0.1-1.5%水、0.05-0.10%檸檬酸(或其他有機酸)及HFA推進劑,其中百分比為以該調配物之總重量計的重量百分比。本發明亦提供包含含有該調配物之罐的pMDI。