Absorption of aerosolized drugs from the rat lung

To investigate the absorption of aerosolized drugs from the rat lung, anesthetized animals were allowed to inhale through a tracheal cannula liquid aerosols of drug solutions generated with an air-jet nebulizer. The aerosols had a mass median aerodynamic diameter of 2.81 +/- 0.08 micron and a geometric standard deviation of 2.53 +/- 0.05. At various times after aerosol inhalation, the lungs were removed and assayed for the amount of compound that had not been absorbed. The times (min) necessary for 50% absorption were: antipyrine, 0.25; salicylic acid, 0.67; barbital, 0.93; amitrole, 1.3; urea, 1.4; procainamide, 2.3; guanidine, 3.1; erythromycin, 6.3; benzylpenicillin, 20.5; p-aminohippuric acid, 21.7; mannitol, 26.5; and N-acetylprocainamide ethobromide, 34.5. Comparison with previously reported absorption rates measured after intratracheal injection of 0.1 ml of drug solution showed that drug inhaled as an aerosol was absorbed roughly two times more rapidly than when administered by intratracheal injection. The results suggest that drug absorption may be more rapid from the alveolar region than from the tracheobronchial region of the lung.