Which Device in Asthma?

The ideal way to deliver drugs in asthma or COPD is by inhalation. A standard dose of salbutamol for inhalation is 100 micrograms compared with 2 or 4mg in tablet form. Hence if drugs can be delivered directly to the lung they will act faster and at a lower dose (20 to 40-fold in the case of salbutamol) which will reduce the incidence of side-effects. However, if the device fails to deliver the drug to the correct place it is of no value at all.

There are a variety of devices available but they can be classified generically as metered dose inhalers (MDI), MDI with spacers, dry powder inhalers (DPI), breath-actuated MDIs (BA-MDI) and nebulisers.

The anatomy of the airways is such that particles tend to be filtered out before they reach the lungs but small particles between 1 and 7 µm in diameter¹ will reach the relevant parts. Larger particles will be filtered out higher up. The speed of the particles and the competence of the inhaler technique are also important.

Metered dose inhalers (MDI)

MDIs are the standard mechanism for delivering drugs to the small airways in asthma or COPD. However, it is essential that the patient is educated in the use of the device and that this competence is checked. As well as education, adequate coordination is required. This must be checked and not assumed. Lack of coordination between activation of the device and inspiration is a major cause of failure of these devices and it is not limited to children.² It is the main cause of poorly controlled asthma.¹ If used properly a MDI is at least as effective as any other form of delivery and much cheaper.³ An American review of the evidence concluded that MDIs are no more or less effective that other systems of delivery and so the least expensive should be chosen.⁴ However, if a cheaper system fails to deliver the drug it is very poor value.

Because of the phasing out of CFCs other propellants have been developed for these inhalers and the evidence suggests that they are just as efficient as the old type.⁵

Spacers with MDI

Most spacers are of large volume, around 750ml, made of plastic and they are inconvenient to carry around. Smaller spacers exist but are probably less effective although this is disputed.⁶ Large spacers usually have a valve system that permits the drug to stay in suspension whilst it is inhaled. The dose may be reduced by accumulation of electrostatic charge so that the drug is absorbed on to the plastic. This can be avoided by periodic washing of the device in soapy water or detergent.

Spacer devices slow down the particles and make coordination of actuation and inhalation much less critical. The main advantage of the spacers is that they increase the proportion of the dose delivered to the airways (where the drugs produce the desired effect), while reducing the proportion absorbed into the body (which is usually the cause of unwanted effects). Metered dose inhalers with large volume spacers deposit at least 30% more drug in the lung but deposit 60% less drug in the patient, because of reduced oropharyngeal deposition.
Any drug that gets into the body but not into the lungs is undesirable. Beta agonists cause tremor and tachycardia. Steroid inhalers can produce oropharyngeal candidiasis and systemic side effects of steroids, including retardation of growth in children.

Bandolier gives the following table to show this effect.^7,8,9,10

A Cochrane review concluded that MDI plus spacer is so efficient for delivering high doses that it is as effective as a nebuliser, much cheaper and does not need a source of power.¹¹ In small children who may be scared of a noisy nebuliser in can be more effective.
Benefits from the use of large volume spacers include:

• More effective treatment with fewer side-effects because of better pattern of deposition
• Problems of poor inhaler technique largely overcome but spacers need to be used properly too
• Easily used by children and the elderly (except those with weak or arthritic hands)
• As effective as a nebuliser in treatment of acute attacks but light, cheap, maintenance free, portable and available on prescription
• Useful for treatment of first attacks of wheezing in patients who have not used inhalers before
• Useful for administration of bronchodilator when testing reversibility in the surgery to establish the diagnosis of asthma
• Reduced prescribing costs by basing treatment on the much cheaper metered dose inhalers

Cough after use of a spacer and MDI is a poorly understood problem that may affect compliance. In one study it affected 30% of children after beta agonists and 54.5% of children after a steroid inhalation.¹²

In January 2006 the volumatic spacer device was reintroduced after the CSM raised concern that the suggested change to the Aerochamber plus might change delivery of drug to the lungs (particularly important for corticosteroids and long-acting B2 agonists). Ironically valve holding chambers (VHC) had been improved in an attempt to give consistent delivery.¹³

Dry powder inhalers (DPI)

These devices can be as small and portable as a MDI but requiring less coordination. Drug delivery to the lungs is dependent upon the patient's peak inhaled flow rate. Over the years devices have improved so that the required rate of inspiration is less and the amount deposited in the lungs is more. They are no more effective than MDI plus spacer and rather more expensive. The most recent devices will still be under patent.
They do not have any propellant, whether CFC or otherwise. Sometimes patients complain that they are not certain if they have taken a dose and devices may be discarded well before they are empty.

Breath-actuated metered dose inhalers (BA-MDI)

These allow patients to prime the inhaler and when the patient takes a breath the inhaler is activated. This avoids the need to coordinate release of the metered dose with breathing. These can be used as second line inhaler devices if there are co-ordination problems with the MDIs after full instruction.¹⁴

Nebulisers

They are usually reserved for delivering high doses of drug in an emergency situation although some people use them for routine therapy. They are large, heavy, expensive, noisy, require a source of power and periodic maintenance.
A wide variety of nebulisers are available. Conventional jet nebulisers waste a great deal of the drug during expiration. Breath assisted open vent systems have considerably reduced this but it is dependent upon the patient having an adequate expiratory flow. Ultrasonic nebulisers produce a high mass output and have a shorter time for treatment but are inefficient for delivering suspensions or viscous liquids. Adaptive aerosol delivering devices release a precise dose that is tailored to the individual's breathing pattern.¹⁵

Both nebulisers and spacers used for small children employ facemasks. There are some significant differences between the characteristics of the various masks effecting efficacy.

It is essential to choose the device that is most suited to the patient. All require a degree of skill and education. A MDI is the cheapest way to provide treatment and many products are off patent. However, quality control of generic products is essential as particle size is crucial to effectiveness. A DPI is small and easily fits a pocket. They are being improved and can easily be mastered. They are more expensive than a MDI. However, any system that fails to deliver the drug to the lungs for that patient is of no value. A MDI with spacer can be as effective as a nebuliser at a fraction of the price and with much less inconvenience. They can replace nebulisers in many instances but not completely. The technology of nebulisers is also improving.

In as many as 50% of cases asthma is poorly controlled.¹⁶
Significant impact on control of the disease can be made by:

• Giving the correct device
• Education of the patient (about their disease and about their device)
• Correct use of the device

In 2002 NICE made a recommendation that children aged 5 to 15 with chronic asthma should usually use a MDI with spacer.¹⁷In 2003 they recommended that under 5 years old the ideal was a MDI, spacer and facemask for chronic, stable asthma. They emphasised the need for compliance and would consider nebuliser or DPI if it produced better results.¹⁸
In 2004 SIGN and the British Thoracic Society produced joint guidance on the management of asthma that included advice about devices. The recommendations were similar to those of NICE (updated Nov 2005).¹⁴