About 70 million people across the world use metered dose inhalers to treat asthma, according to 3M, the company that purchased the inventor of the inhaler. The invention of the pressurised metered dose inhaler revolutionised the respiratory drug field.
In the late 1800s, scientists were already experimenting with aerosols. According to A.R. Clark from Aerosol Science and Technology Journal, "In 1899, Helbing and Pertch described the first aerosol generator to be driven by the vapour pressure of a propellant liquid. They used methyl or ethyl chloride as the propellant and the heat of the hand caused enough pressure to develop to atomise the liquid via a small orifice." In the 1930s and 1940s, freon propellants, the early "aerosols," were invented and used as insecticides.
The Respiratory Care Journal of 2005 reported that in 1955, 13-year-old Susie Maison, the daughter of Riker Laboratories President Dr. George Maison, originated the idea for the inhaler. Susie complained to her father that her asthma medication should be as uncomplicated as her mother's hairspray can.
According to The Respiratory Care Journal, a three-person development team, consisting of George Maison, Charles Thiel and Irving Porush, used an old ice cream freezer, a case of empty perfume vials, a bottle capper and propellants from Dupont to produce the first pMDI prototype. The pMDI evolved to include a 50L metering device developed for the perfume industry, a 10ml amber vial, and a plastic mouthpiece with moulded nozzle to administer salts of isoproterenol and epinephrine. Thiel experimented with these materials and in 1956, he succeeded, inventing the first pressured metered-dose inhaler. According to Respiratory Drug Delivery Online, "Thiel changed the inhaler formulation design from one using 50 per cent alcohol (which burnt patients' nostrils when administered as a nasal spray) to an innovative suspension of the medication in a liquefied gas propellant." Thiel's inhaler carried medication to the lungs more effectively, revolutionising respiratory drug delivery. By 1957, the first oral pMDI's were produced. In 1970, 3M purchased Riker Laboratories and has continued respiratory medicine development to this day.
Inhalers provide asthmatics with quick, portable, efficient doses of medicine. According to Respiratory Care Journal, "Today the pMDI is a pressurised metal canister containing a mixture of propellants, surfactants, preservatives, and drug. The drug represents about 1 per cent of the contents, while the propellants are greater than 80% of the contents, by weight." Inhalers consist of three main parts that hold and dispense medication: a reservoir, a metering valve and a spray actuator.
A common problem with inhalers is still improper use. Inhalation is a complicated science. Alternative Support for Asthma, states, "All too often the puffs are mistimed and only make it part of the way into the airways, and some of the medication is invariably deposited into the mouth and on the back of the throat instead of into the lungs."
"Spacers" or "holding chambers" that slightly delay the medication help ease this problem.