Abstract: The invention is directed to a method for determining the total amount of liquid medicament containing an active drug substance to be aerosolized and inhaled by a patient in order to deliver a pharmaceutically effective amount (“PEA”) of said drug to the respiratory tract of said patient comprising: A) aerosolizing a measured amount of said medicament liquid containing a known amount of drug (“Aerosolized Dose”) using an aerosolization means connected to said patient via an inhalation tube and an exhalation tube; wherein said exhalation tube contains a filter means and wherein said Aerosolized Dose is less than said PEA of said drug; B) administering said aerosol to the respiratory tract of said patient via said inhalation tube; C) allowing the patient to exhale through said exhalation tube containing said filter wherein any exhaled drug is trapped on said filter; D) measuring the reflectance of the color on the filter media contained in said exhalation filter using a reflectance spectrophotometer to determin