A comparison of the availability of tobramycin for inhalation from vented vs unvented nebulizers

To compare drug output from a vented nebulizer (Pari LC Jet Plus) with a traditional unvented nebulizer (Hudson 1730 T Up-Draft 11) using aerosolized tobramycin, which is frequently used in the treatment of cystic fibrosis.

Six nebulizers of each type were filled with a 4 mL tobramycin (80 mg) solution and were driven by a compressor (Pulmo-Aide). Various inspiratory flows (VI) (0, 5, 10, 15, 20 L/min for the Pari LC Jet Plus and 0, 5, and 10 L/min for the Hudson 1730, all at 40% relative humidity) were directed through each nebulizer. Drug output was measured from changes in weight and concentration (assessed by changes in osmometry) within the nebulizer. Particle size distributions were determined by laser diffraction allowing the calculation of the amount of aerosol output in the respirable range (<5 microm). The nebulizers were first run until end-nebulization to establish total drug output and then for either 4 or 5 min to determine the rate of drug output (mg/min) before intermittent aerosol output.

The total drug output without VI for both the unvented and the vented nebulizers was not significantly different, 55 (51, 60) mg for the Hudson 1730 vs 51 (49, 53) mg for the Pari LC Jet Plus (mean [95% confidence limits]). Inspiratory flow had no effect on the unvented Hudson 1730 nebulizer but significantly increased the rate of total drug output and the rate of drug output in the respirable range for the vented Pari LC Jet Plus nebulizer (VI=0, 3.35 [2.84, 3.85] and 1.72 [1.48, 1.96] compared with VI=20, 9.87 [9.03, 10.70] and 6.11 [5.33, 6.88] mg/min).

These findings indicate that the increase in the rate of drug output with VI for the vented nebulizer would result in shorter nebulization times and a relative decrease in drug loss during the expiratory phase.