Despite extensive use of aerosol therapy to treat infants and young ch
ildren with respiratory disease, our knowledge of factors influencing
drug delivery in this age group remains relatively rudimentary. Recent
work with filters used in conjunction with pumps or patients have emp
hasised some of the factors that will maximise the dose inhaled using
different devices though results obtained particularly when used with
patients should be interpreted with caution and in context. There are
few pharmacokinetic or radiolabelled deposition studies on which to ba
se statements regarding dose likely to reach the lungs of children in
this age group. Lung function and clinical results suggest that drugs
can be delivered via nebulisers and holding chambers with face masks a
nd inevitably performance of such devices will vary. However, factors
such as screaming and non-compliance with treatment are likely to infl
uence the lung dose to a great extent. Hence choice of drug delivery s
ystem must be based on patient/parent acceptability as much as on theo
retical grounds. Aerosol therapy in this age group is further complica
ted by our lack of knowledge related to the aetiology of recurrent res
piratory symptoms in young children and hence it is quite likely that
many children are being treated with effective delivery systems but in
appropriate therapeutic agents. Much work is still required before we
have a clear understanding of the aetiology and pathology of the disti
nct sub groups of respiratory disease in young children. Until we have
a greater understanding in this area together with improved understan
ding of delivery systems, drug therapy in this age group will remain v
ery much an empirical art.