A metered-dose inhaler (MDI) is a device that delivers a specific amount of medication to the lungs in the form of a short burst of aerosolized medicine that is usually self-administered by the patient via inhalation.
A metered-dose inhaler (MDI) is a device that is most commonly used delivery system for treating asthma, chronic obstructive pulmonary disease (COPD) and other respiratory diseases.
The medication in a metered dose inhaler is most commonly a bronchodilator, corticosteroid or a combination of both for treating asthma and COPD.
Other medications less commonly used but also administered by MDI are mast cell stabilizers, such as cromoglicate or nedocromil.
A metered-dose inhaler consistshas of three major components: the canister, which is produced in aluminum or stainless steel where the formulation resides; the metering valve, which allows a metered quantity of the formulation to be dispensed with each actuation; and an actuator (mouthpiece) which enables the patient to operate the device and directs the aerosol into the patient’s lungs.
The drug formulation is a liquefied gas propellant and, in many cases, stabilizing excipients.
The actuator contains the mating discharge nozzle and generally includes a dust cap to prevent contamination.
To use the inhaler, the patient presses down on the top of the canister, with their thumb supporting the actuator.
Actuation of the device releases a single metered dose of the formulation, which contains the medication either dissolved or suspended in the propellant.
The breakup of the volatile propellant into droplets, followed by rapid evaporation of these droplets, results in the generation of an aerosol consisting of micrometer-sized medication particles that are then inhaled.
Metered-dose inhaler types of inhaler are the most commonly used type.
The replacement of chlorofluorocarbons propellants with hydrofluoroalkanes (HFA) resulted in the redesign of metered-dose inhalers with smaller aerosol particles being produced and increased in potency by a factor of 2.6.
Asthma inhalers contain medications that treats the symptoms of asthma.
Nicotine inhalers allow cigarette smokers to get nicotine without using tobacco, much like nicotine gum or a nicotine patch.
Dry powder inhalers involve micronized powder, packaged in single-dose quantities in blisters or gel capsules containing the powdered medication to be drawn into the lungs by the user’s breath.
These systems in patients with severely compromised lung function, such as those that occur during an asthma attack, may find it difficult to generate enough airflow to get good function from them.
Metered-dose inhalers can be used to treat COPD, both in a stable state and during lung attacks.
Metered-dose inhalers are sometimes used with add-on devices referred to as holding chambers or spacers.
These are tubes attached to the inhaler that act as a reservoir or holding chamber and reduce the speed at which the aerosol enters the mouth.
They serve to hold the medication that is sprayed by the inhaler, making it easier to use the inhaler and helps ensure that more of the medication gets into the lungs instead of just into the mouth or the air.
Proper use of a spacer can make an inhaler more effective in delivering medicine.
Patients who use corticosteroid inhalers should use a spacer to prevent getting the medicine in their mouth, where oral yeast infections and dysphonia can occur.
A metered dose inhaler contains enough medication for a certain number of actuations (puffs) printed on the canister.
It is important to keep track of the number of times an inhaler is used so that it can be replaced after its recommended number of uses.
Between 50-100% of patients do not use their inhaler devices correctly, with patients often unaware that they are using their inhaled medication incorrectly.
Incorrect inhaler technique has been associated with poorer outcomes.
Components of an MDI include a propellant.
A propellant provides the force to generate the aerosol cloud and is also the medium where the active component must be suspended or dissolved.
Propellants in MDIs typically make up more than 99% of the delivered dose, so the properties of the propellant dominate more than any other individual factor.
Propellants must pass a stringent set of criteria, and they must:
have a boiling point in the range of -100 to +30 °C have a density of approximately 1.2 to 1.5 g cm−3 or approximately that of the drug to be suspended or dissolved have a vapour pressure of 40 to 80 psig have no toxicity to the patient be non-flammable be able to dissolve common additives into
Previously most commonly used propellants were the chlorofluorocarbons.
Hydrofluorocarbon propellants have replaced CFC propellants, but concerns about the use of hydrofluorocarbon propellants have, however, since arisen since these compounds are potent greenhouse gases; propellants released during the use of a single inhaler result in a greenhouse footprint equivalent to greenhouse gases released during a 180-mile car journey.
MDIs are associated with harms related to the environment, public health, and the economy.
MDIs contain hydrofluoroalkalanes, (HFA’s) which have greater than 1000 times the global warming potential of carbon dioxide: makes up 3% of carbon footprint in the UK.
HFA based inhalers account for about 90% of US inhaler prescriptions.