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Inhaler
Therapy
Guidelines for the treatment
of asthma and chronic obstructive pulmonary disease (COPD) recommend
the use of inhaled therapy because it allows a lower dose of drug
to be delivered directly to the lungs than would be possible with
a tablet, and therefore reduces the potential for side effects.
The metered dose inhaler
(MDI) is a pocket-sized, hand-held, pressurised multiple-dose inhal-ation
system which efficiently delivers a consistent, measured dose of
medicine into the lungs.
The MDI has proven safe,
effective and reliable for virtually all patients, and is the mainstay
of successful asthma therapy worldwide. The MDI accounts for approximately
70 percent of all inhalation therapy in the world’s fifteen
largest patient populations.
Essential
Components of an MDI
The essential components
of an MDI are a storage canister; a medicinal formulation, including
both the propellant and the active ingredient; a metering valve
to control the discharge of precise doses of formulation; and an
actuator. The storage canister is placed valve-down into the actuator.
In press-and-breathe MDIs, the patient pushes down on the canister
to release a dose. Breath-actuated MDIs release the required dose
of medication automatically as the patient breathes in.
Inside the MDI canister
is a complex formulation consisting of one or more drug substances;
one or more propellants; and perhaps a co-solvent and/or surfactant.
How
an MDI Functions
The propellant mixture
is made up of one or more liquefied gases which generate a pressure
of 50-80 psi inside the canister. Upon release from the MDI, the
propellant flash evaporates, changing from a liquid to a gas. The
result is a respirable mist of the medicine that was suspended or
dissolved in the formulation.
The function of an MDI is the consistent delivery of an accurate
amount of medication as an aerosol. This allows deposition in the
passageways of the lungs.
Characteristics
of MDIs
The availability of
a wide range of therapy options, including MDIs, dry powder inhalers
and nebulisers, ensures that individual patients receive the best
possible treatment tailored to suit their personal circumstances.
MDIs, often with a spacer or breath activated device, possess numerous
characteristics that, taken together, make them widely acceptable
to millions of patients.
- MDI propellants provide
the energy needed for drug delivery independent of any external
power source or extra inspiratory effort on the part of the patient.
- In MDIs, the delivered
dose depends significantly on the metering valve and formulation,
as opposed to patient inspiration.
- A patient who needs
multiple medications can operate a variety of MDIs using the same
technique.
- MDIs provide good
protection from humidity during use.
- MDIs are widely available
for inhalation of all of the most commonly used respiratory medications.
- MDIs can be adapted
to meet the needs of special patient populations, including young
children and infants, e.g. by adding spacers.
MDIs offer patients
a unique combination of benefits. Thus, they are a vital therapy
option for patients with asthma and other respiratory diseases.
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