The optimum length and width for a spacer device

The aim of this study was to determine the delivery of two different drugs from spacer devices of different lengths and diameter. Spacer devices were prepared from lengths of plastic tubing of length 5, 10, 20, 50 and 100 cm, and diameter 30, 50 and 100 mm. Metered dose inhalers of sodium cromoglycate and budesonide were actuated into the spacers and drug output and particle size were measured using a glass multistage liquid impinger. To determine the effect of delay on the recovery of drug from the spacers, budesonide was actuated into spacers and output measured after a delay of 5, 10 or 20 s. For both drugs, increasing spacer length up to 20 cm increased drug recovery. There was no further increase or reduction with longer spacers. Increasing spacer diameter also increased drug recovery, although the increase was greater for sodium cromoglycate than budesonide. Budesonide delivery was greatest for spacers with a volume of 300 mL or greater, whereas maximum sodium cromoglycate delivery was from spacers with a volume of 1000 mL or greater. Drug half-life was also longer in larger spacers, being 6 s in a 10 cm length spacer (196 mL volume) and 15 s in a 20 cm length spacer (392 mL volume). The optimum spacer size was different for the two drugs. Sodium cromoglycate is best delivered from a larger spacer than budesonide. Conclusions from studies with one drug and spacer combination cannot be applied to another.