MDIs with Spacers and VHCs

The coordination required by the patient to synchronise the actuation of the inhaler with inhalation can be a problem when using pressurised metered dose inhalers (pMDIs) particularly in the young, old or chronically ill. Add-on devices, such as spacers and valved holding chambers (VHCs), eliminate this problem by providing a reservoir of aerosolised particles that during treatment, the patient inhales from via a mouthpiece or facemask.

The new USP draft chapter <1602> for testing “Spacers and Valved Holding Chambers used with Inhalation Aerosols” specifies two tests relating to the Aerodynamic Particle Size Distribution (APSD) of the accessories concerned.

Test Part 1A is designed to measure the APSD from the accessory when used in optimal conditions, that is to say, with no delay following the actuation of the inhaler. Test Part 1B is used in worst case conditions with a delay of 2 or more seconds between inhaler actuation and sampling onset.

A minimum of Cascade Impactor (ACI or NGI), Breath Actuation Controller, Vacuum Pump and Flow Meter are necessary if the requirements of both tests are to be satisfied.

Options are available for testing either mouthpiece-based or facemask-based products.

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