Characteristics of Nebulizers Used in the Treatment of AIDS-Related Pneumocystis Carinii Pneumonia

To characterize aerosolized pentamidine delivery systems, we measured efficiency (drug inspired as percent of dose in nebulizer) and particle size distribution from several nebulizers under simulated clinical conditions. With a piston ventilator, radioactive tracers, and high performance liquid chromatography (HPLC), the Cadema AeroTech II, Marquest Respigard II and Fisons Fisoneb were tested. Each nebulizer was studied with the specific concentration of pentamidine and breathing pattern usually prescribed with the device. We found that each system delivered a significant fraction of respirable particles but there were important differences among nebulizers. With a tidal volume of 750 cc and frequency of 20 breaths/min, the AeroTech II produced a mass median aerodynamic diameter (MMAD) of 1.0 μn, σ = 1.9, efficiency = 21%; the Respigard II MMAD = 0.76 μm, σ = 1.9, efficiency = 4.6%; and the Fisoneb MMAD =2.5 μm, σ = 2.0, efficiency = 16%. The Fisoneb was also tested at a frequency of 12 breaths/ min with an end-inspiratory breath-hold of 3.5 sec without significant changes in MMAD or σ. The size distribution of delivered aerosol was dependent on the type of nebulizer, tubing and attachments, breathing pattern, and presence of medication in the nebulizer. In clinical studies, these factors must be defined before efficacy of a drug can be assessed. Prescribing information should consider the delivery system and its efficiency to prevent inappropriately high or low levels of drug delivery.