Metered dose inhaler - AbsoluteAstronomy.com

A metered-dose inhaler is a device that delivers a specific amount of medication to the airway and lung

Lung

The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s, in the form of a short burst of aerosolized medicine that is inhaled by the patient. It is the most commonly used delivery system for treating asthma

Asthma

Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...

, chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease , also known as chronic obstructive lung disease , chronic obstructive airway disease , chronic airflow limitation and chronic obstructive respiratory disease , is the co-occurrence of chronic bronchitis and emphysema, a pair of commonly co-existing diseases...

(COPD) and other respiratory diseases. The medication in a metered dose inhaler is most commonly a bronchodilator

Bronchodilator

A bronchodilator is a substance that dilates the bronchi and bronchioles, decreasing resistance in the respiratory airway and increasing airflow to the lungs. Bronchodilators may be endogenous , or they may be medications administered for the treatment of breathing difficulties...

, corticosteroid

Corticosteroid

Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex. Corticosteroids are involved in a wide range of physiologic systems such as stress response, immune response and regulation of inflammation, carbohydrate metabolism, protein catabolism, blood electrolyte...

or a combination of both for the treatment of asthma and COPD. Other medications less commonly used but also administered by MDI are mast cell stabilizers, such as cromoglicate

Cromoglicate

Cromoglicic acid is traditionally described as a mast cell stabilizer, and is commonly marketed as the sodium salt sodium cromoglicate or cromolyn sodium...

or nedocromil

Nedocromil

Nedocromil sodium is a medication used to prevent wheezing, shortness of breath, and other breathing problems caused by asthma. It is administered by an inhaler under the brand name Tilade and as an eye drop under the brand name Alocril...

Description

A metered-dose inhaler consists of three major components; the canister which is produced in aluminium or stainless steel by means of deep drawing

Deep drawing

Deep drawing is a sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. It is thus a shape transformation process with material retention. The process is considered "deep" drawing when the depth of the drawn part exceeds...

, where the formulation resides; the metering valve, which allows a metered quantity of the formulation to be dispensed with each actuation; and an actuator (or mouthpiece) which allows the patient to operate the device and directs the aerosol into the patient's lungs.^, The formulation itself is made up of the drug, a liquefied gas propellant and, in many cases, stabilising 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 lower portion of 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. 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.

Uses

Metered-dose inhalers are only one type of inhaler

Inhaler

An inhaler or puffer is a medical device used for delivering medication into the body via the lungs. It is mainly used in the treatment of asthma and Chronic Obstructive Pulmonary Disease . Zanamivir , used to treat influenza, must be administered via inhaler...

, but they are the most commonly used type. The replacement of chlorofluorocarbons propellants with hydrofluoralkanes (HFA) resulted in the redesign of metered-dose inhalers in the 1990s. For one variety of beclomethasone inhaler, this redesign resulted in considerably smaller aerosol particles being produced, and led to an increase of potency by a factor of 2.6.

Asthma inhalers contain a medication that treats the symptoms of asthma.
Dry powder inhaler
Dry powder inhaler
A Dry powder inhaler is a device that delivers medication to the lungs in the form of a dry powder. DPIs are commonly used to treat respiratory diseases such as asthma, bronchitis, emphysema and COPD although DPIs have also been used in the treatment of diabetes mellitus.DPIs are an alternative...

s involve micronised powder often packaged in single dose quantities in blisters
Blister pack
Blister pack is a term for several types of pre-formed plastic packaging used for small consumer goods, foods, and for pharmaceuticals.The primary component of a blister pack is a cavity or pocket made from a "formable" web, usually a thermoformed plastic. This usually has a backing of paperboard...

or gel capsules containing the powdered medication to be drawn into the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s by the user's own breath. These systems tend to be more expensive than the MDI, and patients with severely compromised lung function, such as occurs during an asthma attack, may find it difficult to generate enough airflow to get good function from them.
A nicotine inhaler allows cigarette
Cigarette
A cigarette is a small roll of finely cut tobacco leaves wrapped in a cylinder of thin paper for smoking. The cigarette is ignited at one end and allowed to smoulder; its smoke is inhaled from the other end, which is held in or to the mouth and in some cases a cigarette holder may be used as well...

smokers to get nicotine
Nicotine
Nicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...

without using tobacco
Tobacco
Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...

, much like nicotine gum or a nicotine patch. Nicotine inhalers that are marketed as nicotine replacement therapy
Nicotine replacement therapy
Nicotine replacement therapy is the remedial administration of nicotine to the body by means other than tobacco, usually as part of smoking cessation. Common forms of nicotine replacement therapy are nicotine patches and nicotine gum...

should not be confused with electronic cigarettes, which produce vapour and which are marketed mainly as devices that smokers can use in non-smoking areas.

History

Before the invention of the MDI asthma medication was delivered using a squeeze bulb nebulizer

Nebulizer

In medicine, a nebulizer is a device used to administer medication in the form of a mist inhaled into the lungs....

which was fragile and unreliable. The relatively crude nature of these devices also meant that the particles that they generated were relatively large, too large for effective drug delivery to the lungs. Nonetheless these nebulisers paved the way for inhaltion drug delivery providing the inspiration for the MDI.

MDI's were first developed in 1955 by Riker Laboratories, now a subsidiary of 3M Healthcare

3M Company , formerly known as the Minnesota Mining and Manufacturing Company, is an American multinational conglomerate corporation based in Maplewood, Minnesota, United States....

. At that time MDI's represented a convergence of two relatively new technologies, the CFC propellant and the Meshburg metering valve which was originally designed for dispensing perfume. The initial design by Riker used a glass canister coated with a vinyl plastic to improve its resilience. By 1956 Riker had developed two MDI based products, the Medihaler-Ept containing epinephrin and the Medihaler-Iso containing Isoprenaline. Both products are agonists which provide short term relief from asthma symptoms and have now largely been replaced in asthma treatment by salbutamol

Salbutamol

Salbutamol or albuterol is a short-acting β2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease. It is marketed as Ventolin among other brand names....

which is more selective.

Spacers

Metered-dose inhalers are sometimes used with add-on devices referred to as holding chambers or spacers, which 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. This makes 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. With proper use, a spacer can make an inhaler somewhat more effective in delivering medicine.

Spacers can be especially helpful to adults and children who find a regular metered dose inhaler hard to use. People who use corticosteroid inhalers should use a spacer to prevent getting the medicine in their mouth, where oral yeast

Oral candidiasis

Oral candidiasis is an infection of yeast fungi of the genus Candida on the mucous membranes of the mouth. It is frequently caused by Candida albicans, or less commonly by Candida glabrata or Candida tropicalis...

infections and dysphonia

Dysphonia

Dysphonia is the medical term for disorders of the voice: an impairment in the ability to produce voice sounds using the vocal organs . Thus, dysphonia is a phonation disorder...

can occur.

Lifespan and replacement

The deposition of the content of drug formulation on the canister surface can result in a shorter shelf life of an MDI inhaler

Inhaler

Applying a suitable surface coating to the components helps to extend this shelf life. Over the years a range of coating processes have been developed that can be applied to both the canister and valve to protect the contents from deposition and degradation, the most recent of which being the revolutionary sub-micron plasma process developed by Presspart.
Gas plasma processing is an industrial technique that is carried out in a vacuum to coat the entire MDI inhaler

Inhaler

and involves constant or pulsed excitation of gas by either Radio Frequency (RF) or microwave field to produce an energetic plasma.
This coating ensures that the drug formulation does not stick to the interior wall of the MD inhaler

Inhaler

and results in the patient receiving the prescribed dose of medication, whilst also extending the products shelf life.

A metered dose inhaler contains enough medication for a certain number of actuations (or puffs) which is printed on the canister. Even though the inhaler may continue to work beyond that number of uses, the amount of medication delivered may not be correct. It is important to keep track of the number of times an inhaler was used, so that it can be replaced after its recommended number of uses. For this reason, several regulatory authorities have requested that manufacturers add a dose counter or dose indicator to the actuator. Several inhalation products are now sold with a dose counter-actuator. Depending on the manufacturer and the product, inhalers are sold as a complete unit or the individual canister as a refill prescription.

Propellants

One of the most crucial components of a MDI is its propellant. The propellant provides the force to generate the aerosol cloud and is also the medium in which the active component must be suspended or dissolved. Propellants in MDIs typically make up more than 99 % of the delivered dose, so it is the properties of the propellant that dominate more than any other individual factor. This is often overlooked in literature and in industry because so few propellants are used and their contribution is often taken for granted. Suitable propellants must pass a stringent set of criteria, they must:

have a boiling point in the range -100 to +30°C
have a density of approximately 1.2 to 1.5 g cm⁻³ (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. Active ingredients should be either fully soluble or fully insoluble.

Chlorofluorocarbons (CFCs)

In the early days of MDIs the most commonly used propellants were the chlorofluorocarbons CFC-11, CFC-12 and CFC-114.

Transition to HFA propellants

In 2008 the Food and Drug Administration

Food and Drug Administration

The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

announced that inhalers using chlorofluorocarbon

Chlorofluorocarbon

A chlorofluorocarbon is an organic compound that contains carbon, chlorine, and fluorine, produced as a volatile derivative of methane and ethane. A common subclass are the hydrochlorofluorocarbons , which contain hydrogen, as well. They are also commonly known by the DuPont trade name Freon...

s as a propellant, such as Primatene Mist

Primatene Mist

Primatene Mist is a trade name for an epinephrine metered-dose inhaler sold over-the-counter in the United States for the relief of bronchial asthma. It is manufactured by Armstrong Pharmaceuticals, a company based in Canton, Massachusetts and a subsidiary of Amphastar Pharmaceuticals, located in...

, could no longer be manufactured or sold as of 2012. This followed from the U.S. decision to agree to the 1987 Montreal Protocol

Montreal Protocol

The Montreal Protocol on Substances That Deplete the Ozone Layer is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances believed to be responsible for ozone depletion...

on Substances that Deplete the Ozone Layer.

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.