The meaning of lung dose

For a physician to understand how to prescribe appropriate doses of drugs via aerosol requires a basic understanding of the technical issues involved. Drugs are usually prescribed in terms of “nominal dose” (total dose of drug prescribed). This dose is device‐specific, as recommended doses are different for different devices. The effective component of the nominal dose is the “lung dose”, which is the mass of drug delivered to the lung. A given clinical effect should, in general, be produced by a given lung dose irrespective of the delivery device. However, the effect of a lung dose depends on several factors, including: 1) site of deposition 2) rate of clearance of the drug from airway 3) site of action of the drug. Confirmation that a particular lung dose will produce a desired clinical effect usually requires that a clinical trial be performed. The lung dose should be reflected by data on lung deposition, but interpreting such data requires that the following are considered: 1) Lung deposition figures can be stated in different ways: a) percentage of the nominal dose b) percentage of the mass of drug leaving the aerosolgenerating device c) percentage of the mass of drug entering the mouth or nose. 2) The radiation from an inhaled aerosol is attenuated as it leaves the lung. Approaches vary as to how this correction is done, affecting the quoted data on percent deposition. 3) In children, lung deposition is age‐dependent, but the effect of age on delivery is different for different devices. There are major differences in the efficiency of delivery for different devices with a range of 6–60%. When “adaptive aerosol delivery” nebulizers become available, they should provide an accurate dose of drug to the lung with very low variability. In summary, the concept of lung dose is useful in understanding the related technical aspects, and it has the potential to allow drugs to be prescribed more accurately.