Inhalers breath-activated device

B. J. Lipworth, and D. J. Clark, Lung delivery of salbutamol given by breath activated pressurized aerosol and dry powder inhaler devices, Pulm. Pharmacol. Ther. 70 211 (1997). 

New DPI designs are numerous, with the novelty often associated with the technique for achieving powder aerosolization. Some of the recent patented devices incorporate an additional energy source to supplement the inspiratory force of the patient, in order to aerosolize the drug particles into the inhaled airstream. However, unless the addition energy source is breath activated (e.g. as in Spiros), such devices will be limited by the coordination difficulties typical of the pMDIs. 

Spiros (Dura Pharmaceuticals) is a reusable device containing either a disposable, prefllled plastic cassette with 30 doses or an aluminum blister disk with 16 doses. The device is breath-actuated and the inhalation flow activates a battery-driven motor, which spins an impeller that disperses the drug blend. 

Hanania NA, Wittman R, Kesten S, Chapman KR. Medical personnel s knowledge of and ability to use inhaling devices metered dose inhalers, spacing chambers, and breath-activated dry powder inhalers. Am Rev Respir Dis 1993 147 SSA983. Kelling JS, Strohl KP, Smith RL, Altose MD. Physician knowledge in use of canister nebulizers. Chest 1983 83 612-614. 

To ensure optimal drug delivery, it is necessary to coordinate activation of the inhaler with inspiration and a final hold of breath. Many patients, especially the young and the elderly, find this very difficult and spacer devices are often used between the inhaler and lips these act as an aerosol reservoir and also reduce impaction of aerosol in the oropharynx. Topical deposition can cause local side effects in the mouth, particularly Candida with inhaled glucocorticoids a spacer abolishes this problem. 

Dry powder formulations either contain the active drug alone or have a carrier powder (e.g., lactose) mixed with the dmg. The drug particles must be of sufficiently small aerodynamic diameter to make it to and deposit on the airways. Micronized dry powder can be inhaled and deposited in the airways effectively from DPIs by patients with adequate breathing capacity because they can pull sufficient air through the device. However, young children, some patients with severe asthma, and elderly COPD patients may not always be able to achieve adequate inspiratory flow to ensure optimal medication delivery from DPIs. 

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