Spacers and Valved Holding Chambers

Spacers, primarily valved holding chambers (VHCs), are widely used to overcome some of the problems associated with the use of pressurized metered-dose inhalers (pMDIs). These include the difficulty experienced by patients in trying to coordinate the initiation of inhalation with the actuation of the pMDI. High oropharyngeal deposition of drug, which may result in both local and systemic side effects, is also a problem. Although the variability in output from pMDIs under optimized conditions in the laboratory is low, the variability when used in clinical practice is likely to increase considerably. Hence, the dose introduced into a holding chamber may vary significantly depending on the way in which the pMDI canister is handled before it is actuated. Several studies have shown that various design factors can influence the dose delivered from a holding chamber. These include spacer volume, shape, valve design, using multiple actuations, delay between actuation and inhalation, and construction material, which affects the level of electrostatic charge accumulating on the spacer surfaces. Several spacers which are made from low or anti-static materials are now available. Recommendations for optimal use of spacers, including inhalation techniques are outlined in this chapter, and vary according to patient age and inhalation coordination capability. Efficiency of drug delivery and lung deposition are also dependent on pMDI drug formulation and the patient's anatomical and physiological characteristics.