In vitro performance testing of three small volume-holding chambers under conditions that correspond with use by infants and small children.

The in vitro behavior of three types of small volume-holding chambers intended for use by infants and small children (child AeroChamber, Vent-170 and Space Chamber) has been compared with two pMDI-delivered aerosol formulations (salbutamol: 100 micrograms unit dose and beclomethasone di-propionate (BDP): 50 micrograms unit dose) widely prescribed for this age group of patients. All devices were evaluated using a pediatric breathing simulator that created respiratory conditions likely to be encountered with infants and small children. The filter that collected aerosol delivered from the holding chamber on test was located at approximately the position that the patient's lips would be in the mask, by means of an annular support plate glued into the mask itself. At the lowest tidal volume (50 ml), no salbutamol or BDP was delivered by either the Vent-170 or Space Chamber, whereas the unit doses from the child AeroChamber were 39.7 +/- 1.6 micrograms and 11.8 +/- 1.2 micrograms, respectively. The Vent-170 and Space Chamber delivered measurable doses of both drugs when the tidal volume was increased to 100 ml and again to 200 ml, however, the corresponding doses available from the AeroChamber were always significantly greater. These findings emphasize the importance of designing in vitro tests that mimic use by the patient group for which the device is intended. In vitro measurements made at constant high flow rates in excess of 20 l/min do not reveal these differences in performance that are clinically significant, and may lead the physician to prescribe a device that under certain conditions may not deliver any drug to infants or small children.