Basic Use of Inhalers

Inspiratory Flow Rates

Basic Uses of Inhalers

1 Inhaler medications can be broadly defined under two therapeutic uses:-

1.1 Preventative
A regular dose is administered, often morning and evening, and the treatment aim is to reduce the underlying inflammation that is a feature of respiratory disease. It is of importance that the correct dose is inhaled. Medications frequently used in this indication include steroids, and such drugs can have unwanted effects on the body. Overdosing is not beneficial to the patient, and under-dosing can have serious effects, potentially leading to the onset of asthma attacks.

1.2 Relievers
During an acute asthma attack, the patient is able to administer a medication that provides quick relief from the symptoms they are suffering. Should the patient not respond to treatment, the British National Formulary (BNF Issue 39, March 2000) recommends that "failure to respond adequately at any time requires immediate referral to hospital" (page 131, Management of Acute Severe Asthma in General Practice). It is also recognised that high doses of beta2-stimulants can be dangerous in some patients.

1.3 Since the same inhaler, or same type of inhaler, is used for both purposes it is important that the inhaler can meet the criteria required for them.
Consequently, it should be able to provide:-

1.3.1 A predictable dose on a regular basis.
1.3.2 A sufficient dose when required for relief.

2 Discussion

2.1 Inhaled drug therapy has become the mainstay of treating several respiratory diseases, including asthma and chronic obstructive pulmonary disease. The drug is delivered direct to the target organ, and is therefore effective in smaller doses, compared to administration via oral or injectable form.

2.2 Hand-held inhalers are the most frequently used administration devices. They can be categorised broadly into two groups:-

2.2.1 Pressurised metered dose - which can be further divided into:-

2.2.1.1 Un-adapted - an aerosol cloud leaves the inhaler when the patient depresses the canister.
2.2.1.2 Adapted - the aerosol canister release is triggered automatically once the patient reaches a pre-set inspiratory flow rate.

2.2.2 Dry Powder - the medication is taken from the dosage chamber in the device to the lungs by the action of inhaling through the device during inspiration.

2.3 A consensus of opinion exists amongst clinicians and academics that many patients do not receive optimal inhalation therapy (Inhaler Devices for Asthma, Drug and Therapeutics Bulletin 2000; 38:9-14, Hilton S. An audit of inhaler technique among asthma patients of 34 general practitioners. Br J Gen Pract 1990; 40:505-6).

2.4 It is also widely recognised that incorrect use of an inhaler has a significant effect on the success of treatment (British Thoracic Society, British Paediatric Association, Royal College of Physicians et al. Guidelines for the Management of Asthma Thorax 1993; 48:s1-s24).

2.5 "An ideal inhaler device should deliver a predetermined dose of drug to the lungs, in an easy-to-use, reproducible and cost effective manner, with minimal deposition of drug in other sites. Factors to do with both the patient and the inhaler device can affect drug delivery". (Inhaler Devices for Asthma Drug and Therapeutics Bulletin 2000; 38:9-14).

2.6 The In-Check DIAL, and accompanying chart, has been produced to enable healthcare professionals to identify whether patients are using their inhaler device optimally, and to encourage the patient to achieve the best possible technique for their particular inhaler device. Clement Clarke have reviewed published research for available inhalers, and have sought consultation with researchers in this area of medicine, to ensure that the data presented reflects the performance of each inhaler at different inspiratory flow rates. Full listings of references are available here.