Jane Scullion provides an introduction to the inhaled-device options available for the treatment of respiratory conditions, including COPD and asthma, in the first of a mini-series of feature articles.

scullion jane

Independent content logo

Read this article to learn more about: 
  • the development of devices for delivering inhaled medications for the treatment of asthma and COPD
  • differences between metered-dose and dry-powder inhalers.

 

I nhaled medications are fundamental to the effective management of asthma and chronic obstructive pulmonary disease (COPD). In asthma they save lives, and in COPD they reduce overall symptoms and reduce exacerbations. In these two disorders the administration of medication by inhaler devices has many advantages over oral administration—the inhaled route has a quicker onset of action and it is associated with less systemic side-effects, resulting in fewer overall side-effects.1

Device choice and medication options were limited for many years; more recently the market has grown considerably in terms of devices, new formulations, combinations of medications, and new licensing opportunities for indications. Although this has meant an increase in the treatment options available for patients, as Andrew Booth (advanced nurse specialist at York Teaching Hospital) explains ' … this can mean that staying ahead of current respiratory pharmacology is challenging … '.2

Despite the plethora of devices that are now available and which vary in their degree of sophistication, for example, those that provide feedback, count dose, or lock out once the dose has been taken, they all fall within one of two categories—metered-dose inhalers (MDIs), which contain a liquid aerosol, or dry-powder inhalers (DPIs).

Metered-dose inhalers

Using an MDI, by inhaling a short burst of aerosolised medicine, a patient is able to receive a specific amount of medication directly into the lungs. In 2005 it was reported that MDIs were the dominant form of treatment for asthma and COPD globally.3 At this time the proportion of MDI to DPI use was 7:3 in the UK.3 Medications administered via an MDI are most commonly bronchodilators, corticosteroids, or a combination of both of these, for treating asthma or COPD. Other medications administered by an MDI include the mast-cell stabilisers cromoglycate and nedocromil.

History of MDIs

Previously asthma medication was delivered using a squeeze bulb nebuliser, which was fragile and unreliable.4 The particles generated were too large for effective drug delivery to the lungs.5 Nonetheless these nebulisers led the way for inhalation drug delivery, and ultimately to the initial development of the MDI by Riker Laboratories (now a subsidiary of 3M Company).4 The initial development of this device brought together two recent advances in technology—the Meshburg metering valve (initially designed to dispense perfume) and chlorofluorocarbon (CFC) propellants.6 The device was approved in 1956, and in the same year two MDI-based products were launched. These products delivered adrenaline, a non-selective adrenergic agonist, and isoprenaline, a non-selective beta-adrenergic agonist, respectively—which both provided short-term relief from asthma symptoms. In subsequent years, these medications were superseded by the selective short-acting beta agonist (SABA) salbutamol, and inhaled corticosteroids (ICSs)—these formed the cornerstone of asthma management.7 More recently, long-acting preparations have added to our armoury of therapy choices.

In 1987 the Montreal Protocol was developed by the United Nations to address the harmful effects of CFCs on the ozone layer. As a result, hydrofluoroalkanes (HFAs) gradually replaced CFCs as propellants in MDIs.8

Dry-powder inhalers

In a DPI the medication being delivered is formulated either as pure drug or as a mixture with an inactive excipient, such as lactose.9 The generation of a drug aerosol in a DPI is driven by the patient's inhalation; consequently, there is no requirement for an aerosol propellant, or for coordination between device activation and inhalation.10 However, if a patient using a DPI is unable to generate the inspiratory flow required delivery of the drug may not be optimal.10 Medications delivered by DPIs are similar to those delivered by MDIs, and include bronchodilators and corticosteroids in varying combinations.

History of DPIs

An inhaling apparatus for the delivery of dry powder medications was patented by Alfred Newton in 1864. The principles underlying this development still apply today—the powder needed to be kept dry, and had to be finely pulverised.11 In the 1940s, the Aerohalor® was launched for penicillin G powder; in the 1950s, this device went on to be used for the delivery of isoprenaline for the treatment of asthma.8 It was considered that the Aerohalor® was the first commercially available DPI.6

Effective inhaler use

The total lung deposition of an inhaled drug is strongly affected by the speed of inhalation. Consequently, the inhalation rate is important when patients use an inhaler device—MDIs and DPIs require different inhalation rates.

MDIs, require a slow and steady inhalation, with an inhalation rate <90 l/minute.12 The device creates an aerosol—a slow and steady inhalation ensures that the drug goes to the peripheral airways instead of the mouth or throat.10 DPIs require an inhalation that is 'as deep and hard as you can'—the inhalation rate should be >30 l/minute. In order to create particles that are small enough to penetrate the peripheral airways and be deposited in the lungs, the inhalation rate needs to be sufficient to generate a turbulent force in the inhaler to break up the formulation.12 Due to the aerosol effect in MDIs, meaning the inhalation of liquid can be felt, many people believe that they contain more medication than DPIs. To address this some newer DPIs have added a taste to the dry powder as a feedback mechanism.

Both MDIs and DPIs have benefits and failings, so perhaps the most important consideration is that the person can actually use the inhaler properly and that they have the correct medication in the chosen device. Irrespective of the device chosen there are certain steps to usage that all the devices have in common (see Box 1 below).13

Box 1: 7 SIMPLE steps to inhaler devices13

  • Prepare inhaler device
  • Prepare (or load) dose
  • Breathe out (not into inhaler)
  • Put lips around mouthpiece
  • Breathe in:
    • MDI: slow and steady
    • DPI: quick and deep
  • Remove inhaler from mouth and hold breath for up to 10 seconds
  • Repeat as directed.

MDI=metered-dose inhaler; DPI=dry-powder inhaler.

Simple Steps Education. Inhaler technique – 7 steps to success reminder cards. www.simplestepseducation.co.uk
Reproduced with permission

It should also be remembered that inhalation rates will be different for every individual. When deciding which inhaler device to select for our patients we need to consider whether the device can be used by the person. In accordance with the BTS/SIGN British guideline on the management of asthma, inhalers should only be prescribed to patients once they have received training in the use of the device, and have demonstrated satisfactory technique.14 Additionally the NICE guideline on Chronic obstructive pulmonary disease in over 16s: diagnosis and management recommends that a patient's ability to use an inhaler should be assessed at regular intervals by a competent healthcare professional with the correct technique being re-taught as necessary.15

See the second article in this mini-series where Jane Scullion considers the increasing number of different inhalers that are available, and the pharmaceutical options they offer in treating patients.

View related respiratory content

References

  1. Scullion J, Holmes S. Maximizing the benefits of inhalation therapy. Practice Nursing 2013; 24 (12): 592–598.
  2. Booth A. Using an inhaler. Respiratory Care Today 2015; 1 (1): 44–47.
  3. Metz B, Kuijpers L, Solomon S et al (Authors). Safeguarding the ozone layer and the global climate system: issues related to hydrofluorocarbons and perfluorocarbons (SROC). Cambridge: Cambridge University Press, 2005: chapter 8. Available at: www.ipcc.ch/report/sroc/ (accessed 16 March 2016).
  4. Purewal T, Grant D. Metered dose inhaler technology. CRC Press, 1998.
  5. Swarbrick J. Encyclopedia of pharmaceutical technology. Informa Healthcare, 2006.
  6. Clark A. Medical aerosol inhalers: past, present, and future. Aerosol Science and Technology 1995; 22 (4): 374–391.
  7. Crompton G. A brief history of inhaled asthma therapy over the last fifty years. Primary Care Respiratory Journal 2006; 15: 326–331.
  8. Anderson P. History of aerosol therapy: liquid nebulization to MDIs to DPIs. Respiratory Care 2005; 50 (9): 1139–1150.
  9. Newman S, Busse W. Evolution of dry powder inhaler design, formulation, and performance. Respiratory Medicine 2002; 96: 293–304.
  10. Capstick T, Clifton I. Inhaler technique and training in people with chronic obstructive pulmonary disease and asthma. Expert Review of Respiratory Medicine 2012; 6 (1): 91–101.
  11. Sanders M. Inhalation therapy: an historic review. Primary Care Respiratory Journal 2007; 16 (2): 71–81.
  12. Al-Showair R, Tarsin W, Assi K et al. Can all patients with COPD use the correct inhalation flow with all inhalers and does training help? Respiratory Medicine 2007; 101: 2395–2401.
  13. Simple Steps Education. Inhaler technique – 7 steps to success reminder cards. www.simplestepseducation.co.uk/
  14. British Thoracic Society/Scottish Intercollegiate Guidelines Network. British guideline on the management of asthma. SIGN 141. Edinburgh: 2014. Available at: www.sign.ac.uk/pdf/SIGN141.pdf
  15. National Institute for Health and Care Excellence. Chronic obstructive pulmonary disease in over 16s: diagnosis and management. Clinical Guideline 101. London: NICE, 2010. Available at: www.nice.org.uk/guidance/CG101 (accessed 18 May 2016). G