Comparative studies on Metered dose inhalers and Dry powder inhalers

Inhalers used for asthma can be classified into two categories: Metered dose inhalers (MDIs) and Dry powder inhalers (DPIs). Metered dose inhalers are usually used as asthma rescue inhalers or reliever medicines. There are breath-actuated autohalers that release the medication when you breathe in, and there are non breath-actuated pressurized inhalers in which the medication is released by pushing the canister down into the holder. They are all bronchodilators and are either short or long acting beta agonist inhalers or inhaled corticosteroids. Below are pictures of metered dose inhalers

ProAir HFA inhalerProAir HFA


Maxair inhaler



Xopenex inhaler​Xopenex


Dry powder inhalers are a group of inhalers that have the medication in very fine dry powder format. They are classified into single dose devices, multiple unit dose devices and multi dose devices. These tend to be more popular with patients because they are all breath actuated. They are usually used for long-term asthma management. Below are pictures of dry powder inhalers.

Advair Diskus inhaler​ Advair Diskus


Asmanex Twisthaler inhaler​ Asmanex Twisthaler


Pulmicort Flexhaler inhaler​ Pulmicort Flexhaler


The active ingredients in MDI inhalers are dissolved or suspended in a propellant, a mixture of propellants, or a mixture of solvents and they are delivered via a compact pressurized aerosol dispenser. The dispenser can hold about several hundred metered doses of the medication. DPI inhalers contain the medication in a fine dry powder format and the medication is delivered to the lungs as the patient inhales through it. It contains the medication without any propellants. There are pre-metered DPIs which contain previously measured doses in blisters, capsules, etc. and they are inserted into the device during the manufacturing process or by the patient before use. The dose is inhaled directly from the pre-metered unit or it might be transferred to a chamber before being inhaled. There are also device-metered DPIs that have an internal reservoir containing multiple doses that are metered by the device itself during actuation by the patient.

MDI and DPIs have their advantages and disadvantages. MDIs require the user to coordinate pressing down the canister and inhaling the medication while DPIs do not; however, the inspiratory flow rate is a drawback of DPIs. The rate required to deliver the medication in MDI inhalers is about 30L/min while the rate required for DPIs is higher (ranging from 30-120L/min) and differs based on the build of the inhaler. This higher rate would make it more difficult for small children to be able to receive the medication properly. Using DPIs also requires the patient to be careful not to disperse medication via exhalation into the device prior to using. MDIs have a high percentage of patients misusing them, which can lead to inhaler overdose or can cause the patient to receive less than the proper amount of medication and when using an inhaled corticosteroid, it can cause oral thrush.

Another disadvantage to using MDIs is the propellant; previously chlorofluorocarbon (CFC) was used but because it has been shown to deplete the ozone layer, hydrofluoroalkane (HFA) is now used and can cause the inhaler to be more expensive. DPIs have some additional disadvantages as well; because of the wide range of DPI designs, there are challenges in developing information and instructions in support of the device and the functionality of the device might not last as long as an MDI. DPIs are also more susceptible to contamination because of their design and drug delivery method whereas MDIs are not; DPIs also contain lactose, though in small amounts. DPIs are generally more expensive to produce as well. Table 1 compares MDIs and DPIs, describes how to use the inhalers, and gives the name of some drugs that are useful for each kind of inhaler.

Table 1: Comparison of MDIs and DPIs


BuildPressurized aerosol dispenserVarious forms such as Rotahaler, Turbuhaler, Diskhaler, Handihaler

Breath Actuated or Non Breath ActuatedBothBreath Actuated

Syncing of Breath RequiredYesNo

Inspiratory Flow30L/min30-120L/min

Usage TechniquesPress down the top of the medication canister and at the same time inhale deeply and slowly through the mouth until the lungs are completely filled, hold the medication for as long as possible and exhale. Repeat if needed after waiting about 1 minute; can also be used with a spacer (see diagram below)Differ depending on device but general instructions are:
1) For single use devices, load a capsule into the device as directed.
2) Breathe out slowly and completely
3) Seal the lips around the mouthpiece.
4) Breathe in through the mouth quickly and deeply over two to three seconds.
5) Hold your breath for as long as possible then breathe out slowly.

Drugs it is Useful ForProAir HFA, Proventil HFA, Ventolin HFA, and XopenexAdvair, Asmanex, and Pulmicort


asthma_article_effect_fig1Using an Inhaler with a Spacer


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