Respiratory tract deposition of 99mTc-labelled drug particles administered via a dry powder inhaler

Abstract

Drug particle deposition in respiratory tract after inhalation from dry powder inhaler was evaluated. Disodium cromoglycate particles were labelled with a pure γ-radiator, 99mTc, using a co-precipitation technique based on spray drying. Labelled drug particles were mixed with lactose, packed in gelatin capsules and inhaled using the dry powder inhaler. Fractional deposition in the whole lung area, upper airways and stomach as well as in the inhaler was monitored using a gamma camera. Inhalations of 7 patients showed that on average 16.4% of the dry powder dose was deposited in bronchial and alveolar stages of the lungs. This fraction is almost twice as large as the previously reported lung depositions after administration from the metered dose asthma aerosols. The majority of the drug not deposited in the lungs remained in the inhaler. Thus there was clearly less of the untherapeutically used drug in the mouth, oesophagus and stomach than after administration from metered dose aerosols. The results pointed out a better bioavailability of the drug dose administered with the dry powder drug from than with the conventional metered dose aerosol drug form. The behaviour of the drug particles during the inhalation is, however, strongly dependent on the formulation of the powder mixture as well as on the construction of the powder inhaler.