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The pressurized metered dose inhaler (pMDI) has been widely used for more than 60 years. How has it evolved since 1956, and how might it evolve further? 12 OctOber 2017 Inhalation The pressurized metered dose inhaler: Past, present and future perspectives The pressurized metered dose inhaler has been widely used for more than 60 years. How has it evolved, and how might it evolve further? Stephen P. Newman, PhD Scientific Consultant The first pMDIs Technical innovations can be classified as sustaining, disruptive or revolutionary, 4 with most innovations being sustaining. e pMDI was a disruptive innova- tion when introduced in 1956, because it allowed users to address the challenge of drug delivery to the lungs in a radically new way. e pMDI is a complex device with several key components, including formulation and metering valve (Figure 1). Fortuitously, its development coincided with the recent availability of suitable 50 µL Introduction: Fumes, vapors and nebulizers Inhaled drug delivery has a rich history extending over thousands of years, 1 but for much of this time it involved burning plant materials and inhaling the fumes. The development of the first "atomizers" to deliver water droplets at thermal spas in Europe in the 19 th century signaled a clear shift away from vapors towards aerosols. From this beginning, a range of inhaler devices has evolved, and continues to evolve today. 2 ere are several driving forces behind this evolution, reflecting the needs (a) to develop convenient and affordable inhalers that patients will use and can use correctly, (b) to deliver an increasingly wide range of drugs by inhalation, and (c) for some drugs, to improve the efficiency of drug delivery and make it less variable. e field is dominated by the mainte- nance therapy of asthma and chronic obstructive pul- monary disease (COPD), but the pulmonary route is also used to deliver drugs to treat several less common lung diseases, as well as being a portal of entry for drugs required to act systemically. e use of hand-held, squeeze-bulb nebulizers to deliver inhaled epinephrine for treatment of asthma attacks was first reported in the early 20 th century, and this practice became more common as the century progressed. e glass DeVilbiss no. 40 nebulizer (available in the 1930s) and other similar models became well known. But these devices suffered from two important limitations: they were fragile and easily broken, and they delivered a vari- able dose that depended on the amount of pressure applied. It was the desire of Riker Laboratories in the mid-1950s to provide patients with a more robust and reliable dosage form that led scientists there, including Charles iel and Irving Porush, to invent the first pres- surized metered dose inhalers (pMDIs) in 1956. 3 e pMDI has recently celebrated its 60 th birthday. Valve Formulation Actuator Canister Figure 1 Schematic of a typical pMDI. Key components are the canister, actuator, formulation and metering valve. Although the pMDI now looks much the same as it did in 1956, the device has undergone many changes and improvements. Originally published in Bell and Newman, Expert Opin. Drug Deliv. 2007; 4: 215-234; www.tandfonline.com.