METERED DOSE INHALER: A REVIEW

Abstract

Pressurized metered dose inhalers (pMDI) are portable, convenient, multi-dose devices used to administer aerosolized drugs that use a propellant, and delivered a fixed dose of medication with each actuation. They have a metallic chamber containing a suspension or solution. A key piece in this system is the dosage valve, which releases at each pulse a controlled, reproducible dose of medication. The drug is released at a high speed (at more than 30m/s through the mouth-piece) and in the form of particles with an MMAD of between 2 and 3µm. Chlorofluorocarbon propellants are being replaced by hydrofluoroalkane propellants that do not have ozone depleting properties. Two new propellants have been approved for CFC substitutes: hydrofluoroalkane HFA-134a and HFA-227ea. The change from CFCs to HFAs in metered-dose inhalers was not a straight forward exchange. Indeed, substantial new technology had to be developed to make the HFAs suitable for use in metered-dose inhalers. More significant advances, related to the direct operation of metered-dose inhalers. Based on this objective, breathactuated pressurized inhalers, breath-coordinated metered-dose inhalers, and velocity-modifying inhalers were developed. Recent advancements in pMDI technology associated with the transition to HFA propellants have resulted in highly efficient pMDI systems that are broadly applicable to treating a wide variety of diseases.