Breath-Actuated MDIs

This is a compact device (Fig. 7) it is quiet in operation and functions at a low inhaled flow rate that is easily achieved by patients with obstructive airways disease (67). 

The features that distinguish it from a standard inhaler are that  

The aerosol canister is completely enclosed within the body of the device. There is a latching lever at the top of the inhaler, which the patient lifts to prime the device prior to inhalation. 

Marcel Dekkbr, Inc. 270 Madison Avenue. New York, New York 10016 

The act of inhalation actuates the metering valve and allows a dose of drug to be released, eliminating the need for coordination. 

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The breath-actuated MDI Autohaler, is cocked with a lever to load the dose of medication, a baffle is opened by inspiratory pressure, and the dose is expelled from the canister metering chamber. " While the need for hand-lung coordination for proper actuation is reduced significantly with breath-actuated MDIs, these devices do not allow the use of a spacer device. 

Difficulties in the way patients use MDIs has been one factor in the development of other forms of inhaler, in particular dry-powder inhalers (DPIs) and breath-actuated MDIs. These newer devices produce better compliance in terms of techrfique (whether they affect other reasons for noncompliance is less clear), but even here, some are better than others. One study of dry-powder inhaler technique found that that 5% had good technique, 5% were adequate, and 27% were insufficient (39). For example, in the case of DPI, it is necessary to inhale reasonably fast, though the extent to which the rate of inhalation affects deposition varies between inhalers. Some DPIs show less variation and are tolerant of lower inhalation rates compared with others. The wide range of inhalers now available varies on a number of different criteria, and some inhalers will be more suited to some patients than others. Devices may not be equally suited to children, young adults, or the elderly. 

Aerosolized medications are available as pressurized or breath-actuated metered-dose inhalers (MDIs), dry powder inhalers (DPIs), and nebulized or wet aerosols. Most inhaled medications currently used are available as metered-dose inhalers (Table 3). For the patient who has difficulty to coordinate activation of a MDI, a spacer improves delivery. Spacers reduce deposition of the drug in the... 

MDI, breath actuated >5 years Slow (30 1/min or 3-5 s) inhalation Indicated for patients unable to... 

Another very elegant and highly portable device that aids patient coordination is the breath-actuated inhaler, originally developed by Riker Laboratories (3M) [47] and further enhanced by Ivax-Norton (EasiBreathe). In this type of device, a mechanical release mechanism is used, firing the MDI when a certain threshold inspiratory flowrate is reached. Once the dose has been dispensed, the device is then reprimed, ready for use. This type of device has gained wide acceptance in Europe and has been introduced for several MDI products. 

To avoid the need for coordination in breathing and actuation of the inhaler, a breath-actuated system has been devised. Patients who inhaled at 50 L/min did not experience significantly greater bronchodilation using a breath-actuated device than those using a conventional MDI [173], The Autohaler, shown in... 

Dry micronized powders can be inhaled directly into the lung. Four DPIs for asthma are available for use in the United States (i.e., Diskus, Rotahaler, Turbuhaler, and Aerolizer), with others under development. " Each has unique characteristics with advantages and disadvantages (Table 26-5). The primary advantage of DPIs is that they are breath-actuated and require minimal hand-lnng coordination. Some DPIs are more flow-dependent than others. Thus, similar to MDIs and spacers, delivery data from one DPI cannot be extrapolated to another. 

The SmartMist (Aradigm Corporation, Hayward, CA) is a hand-held breath-actuated microprocessor-controlled accessory for use with MDIs. The device is shown in Fig. 9. It can be loaded with some of the standard pMDI canisters. It con-... 

Bronchodilators may be administered via MDIs or nebulization with equal efficacy. Nebulization may be considered for patients with severe dyspnea who are unable to hold their breath after actuation of an MDI. 

SAACh/SAACh combined followed by 10 s breath holding. Open mouth technique holding MDI 2 inches away from open mouth, is comparable to closed-mouth technique (closing Ups around MDI mouthpiece) requires lower doses per actuation... 

The dose and frequency of bronchodilators are increased during acute exacerbations to provide symptomatic rehef. Short-acting j32-agonists are preferred because of their rapid onset of action. Anticholinergic agents may be added if symptoms persist despite increased doses of )52-agonists. Bronchodilators may be administered via MDIs or nebulization with equal efficacy. Nebulization may be considered for patients with severe dyspnea who are unable to hold their breath after actuation of an MDI. 

MDIs, as with other devices, are subject to misuse by patients. The administration problems associated with the delivery of aerosols from MDIs generally appear to be related to inappropriate technique, particularly coordination of breathing and actuation [169-171]. There are particular problems in the use of this technique by children, who may not respond as readily to instruction [172], Also of note, there is still some debate on the most appropriate methods of administration, particularly with respect to the use of different drugs. 

Metered-dose inhaler (MDI) Canister held inverted Formulation (CFC, HFA, solution, suspension) Actuator cleanliness Addition of a spacer device Inspiratory flow (slow, deep) Breath-holding Coordinating actuation with inhalation Priming and shaking the device... 

Riker Laboratories, now 3M Healthcare, invented the pressurised metered dose inhaler (MDI) in 1955 when they combined the atomising power of CFCs and a metering valve design. The great majority of valves still use this basic retention valve principle, and hence pressurised MDIs (pMDIs) are all similar in appearance and operation when used with a standard actuator in the normal press and breathe manner. 

The hardware for a pMDI (Figure 10.7) is as crucial as, or perhaps even more important than, the formulation. A normal press and breathe MDI consists of the can, valve and actuator (also sometimes called an adapter). The three components are sourced externally. 

The most common errors are the inability to coordinate inhalation with MDI actuation, to inhale too quickly, and to exhale without a breath-hold (12,49,50). Crompton (49) identified 215 patients with inadequate inhaler technique. Of these, 50% failed to synchronize aerosol release with inhalation and 36% stopped inhaling when the propellant spray hit the back of the throat. Patients may stop breathing in when propellants impact on the back of the throat and rapidly evaporate, causing almost instantaneous cooling in that area. This is known as the cold freon effect (51). It is difficult to argue with the advice that old patients, young patients, and anyone else should be assumed to be unable to use pMDIs properly unless proved otherwise (49). Nasal inhalation is also a common error among children (51). 

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