LUNG DEPOSITION PATTERNS OF DIRECTLY LABELED SALBUTAMOL IN NORMAL SUBJECTS AND IN PATIENTS WITH REVERSIBLE AIR-FLOW OBSTRUCTION

Background-Earlier studies of aerosol deposition in the lungs have rel ied on indirect labelling of Teflon spheres of a similar size distribu tion to the drug in question and have assumed similar aerodynamic prop erties. Using a modification of a new technique for directly labelling salbutamol, the deposition of salbutamol within the lungs of normal s ubjects and patients with asthma has been studied with the use of a me tered dose inhaler (MDI) alone, an MDI with a spacer device, and a dry powder inhaler (DPI). Method-Salbutamol was directly labelled with te chnetium-99m and placed in an MDI or DPI. Ten normal subjects and 19 p atients with asthma inhaled 200 mug of salbutamol by means of the MDI alone, the MDI with a spacer device attached, and by DPI on separate d ays. Deposition was assessed by a dual headed gamma camera after inhal ation of the drug. Results-The total mean (SD) percentage deposition o f the drug in the normal subjects was 21.6% (8.9%) with the MDI alone, 20.9% (7.8%) with the MDI with spacer, and 12.4% (3.5%) with the DPI. For the patients, the mean percentage deposition was 18.2% (7.8%) wit h the MDI alone, 19.0% (8.9%) with the MDI and spacer, and 11.4% (5.0% ) with the DPI. Bronchodilatation achieved by the patients was similar with all three techniques. Mean peripheral lung deposition was signif icantly greater with a spacer device than when the MDI was used alone in both normal subjects (49.4% (6.1%) v 44.1% (9.9%)) and patients (38 .6% (11.1%) v 30.4% (9.4%)). Conclusions-The deposition of directly la belled salbutamol from an MDI is greater than previously estimated by indirect labelling techniques. The deposition of labelled salbutamol f rom a DPI, however, is little different from that measured by indirect techniques.