Actual pentamidine dose delivered by Respigard II nebulizer.

The Respigard II nebulizer system is the approved method to deliver pentamidine aerosols in the USA. Although continuous operation of the nebulizer until dryness is a designated regimen, the actual pentamidine dose delivered under the operating condition has not been thoroughly studied. Pentamidine solutions (300 mg in 6 mL water) were nebulized continuously with the Respigard II nebulizer system until dryness (40 min operation). Aerosols were delivered to the lower airways via an oropharyngeal model and sampled on a filter with a standard breathing mode of 20 breaths.min-1 frequency and 750 mL tidal volume. Intermediate samples were also obtained for the initial 20 min delivery. The pentamidine dose delivered to the mouth was 1.6% of the dose placed in the nebulizer. Of the dose delivered to the mouth, 92% was delivered during the initial 20 min period. Aerosol loss in the oropharyngeal model was 15% of the dose delivered to the mouth or 0.24% of the dose initially placed in the nebulizer. Pentamidine dose delivered to the lower airways was a very small fraction of the initial dose in the nebulizer. A partial delivery for the initial 20 min was nearly comparable to complete delivery.