Nebulised pentamidine as treatment for Pneumocystis carinii pneumonia in the acquired immunodeficiency syndrome.

Nebulised pentamidine as treatment for Pneumocystis carinu pneumonia in the acquired immunodeficiency syndrome SIR,-Dr Miller and his colleagues (July 1989;44:565-9) report that nebulised pentamidine when delivered by a Respirgard II nebuliser is more effective in the treatment of Pneumocystis carinii pneumonia than when delivered by an Acorn nebuliser.They state, however, that the mass median aerodynamic diameter (MMAD) of the aerosol produced by the Acorn is 2-6 pm.This means that 50% ofthe aerosol mass is contained in droplets ofless than 2-6 pm and 50% of the aerosol mass is contained in droplets of 2-6 pm or more.It is therefore a physical impossibility for 46% of the particles to be less than 3 9 pm, as the authors state.If this latter figure is correct, then the MMAD of the aerosol must be 3 9 pm or more.The correct size of the aerosol is critical to the interpretation of this study.Newman and colleagues have shown that the MMAD of the Acorn nebuliser, when measured in the same manner, ranges from 4 5 to 5-7 pm.'It seems likely that Dr Miller and his colleagues have miscalculated the MMAD.Only one patient from the group treated by Acorn nebulisers was seen to have oozing and contact bleeding at bronchoscopy, whereas four patients from the Respirgard group, which delivers a smaller droplet aerosol, were noted to have these findings.It is therefore difficult to implicate the pentamidine as the cause of these abnormalities, as the larger aerosol (delivered by the Acorn nebuliser) would be expected to produce a greater upper airway deposition, and so cause more rather than less mucosal irritation.Moreover, the authors state that the diagnosis of pneumocystis pneumonia was made by bronchoscopy before pentamidine was started (with the exception of one patient treated empirically).How is it then possible for the nebulised pentamidine to have caused the mucosal friability attributed to it?