Background-Aerosols generated from metered dose inhalers may be highly charged. The aim of this study was to determine whether lining the walls of a polycarbonate spacer device with an antistatic agent would result in an increase in drug output. The effects of multiple actuations of drug into the spacer device and increasing residence time of drug within the spacer were also determined. The key features of a spacer device are a chamber or reservoir where the discharged aerosol cloud can be held, and a one way demand valve which allows air to be drawn through the chamber on inspiration but prevents air passing through the chamber on expiration. These devices may be modified by adding a face mask to allow use by preschool children as an alternative to nebulisation.1Comparative studies between sodium cromoglycate 1 mg and 5 mg metered dose inhalers have confirmed that the 5 mg inhaler is clinically more effective and has a longer duration of action. Knowledge of the dose of sodium cromoglycate available for patients to inhale therefore appears to be important. A polycarbonate large volume spacer device has been developed (Fisonair; Fisons Ltd) for the delivery of sodium cromoglycate. Little is known about the output of sodium cromoglycate (5 mg) from this device, however, or how best to use it. For example, aerosol particles generated from a metered dose inhaler are highly charged and may be attracted electrostatically to the polycarbonate walls of the spacer device, decreasing the amount of drug available for inhalation.In addition, many patients prescribed two actuations of sodium cromoglycate via a spacer device will actuate twice into the device and then inhale as this is more convenient. Mothers of young children often actuate drug into a spacer device and allow several seconds to elapse before they can coax their child to breathe adequately from the device. The effect of these techniques on drug output is not known.The purpose of this study was to determine: (1) whether lining internal walls of a spacer device with an antistatic agent would reduce electrostatic deposition of particles and thus increase the dose available to patients for inhalation; (2) the effect on the therapeutic dose of delivering multiple actuations of sodium cromoglycate (5 mg per actuation) into the spacer device before inhaling the aerosol cloud; (3) the effect on the available therapeutic dose of the time the drug resides in the spacer device before inhalation. (Thorax 1993;48:603-606)

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