Propellant-driven metered-dose inhaler

Fig. 4 (A) Propellant-driven metered dose inhaler. (B) Metering valve.

AJ Hickey, RM Evans. Aerosol generation from propellent-driven metered dose inhalers. In AJ Hickey, ed. Inhalation Aerosols. New York Marcel Dekker, Inc., 1996, pp. 417-439. 

To measure lung deposition by imaging, the aerosol must be first labelled or tagged with a suitable radionuclide. Radiolabelling techniques have been developed for current inhalation products including nebulizers, propellant-driven metered dose inhalers, and dry powder inhalers. 

Propellant-Driven Metered Dose Inhalers (MDIs)... 

Smyth HDC. The influence of formulation variables on the performance of alternative propellant-driven metered dose inhalers. Adv Drug Delivery Rev 2003 55(7) 807-828. 

Smyth, H. D., Beck, V. P, Williams, D., and Hickey, A. J. (2004),The influence of formulation and spacer device on the in vitro performance of solution chlorofluorocarbon-free propellant-driven metered dose inhalers, AAPS PharmSciTech, 5, E7. 

Pharmaceutical inhalation aerosols are widely used for treatment of diseases such as asthma and chronic bronchitis. There are three basic types of aerosol products the propellant-driven metered-dose inhalers, the dry powder inhalers, and the nebulizers. Because of the ozone-depleting and greenhouse effects of the chlorofluorocarbon (CFG) propellants, interest in the dry powder aerosols has risen in recent years. 

Hickey, A.J. Evans, R.M. Aerosol generation from propellant-driven metered dose inhalers. In Inhalation Aerosols Hickey, A.J., Ed. Marcel Dekker, Inc. New York, 1996 417 39. 

Radiolabeling of nebulizer solutions, propellant-driven metered-dose inhalers, and dry-powder inhalers is... 

In particular, the propellant-driven metered-dose inhalers release the aerosol cloud at the very high velocity caused by the pressure of the propellant. The open-mouth technique of inhalation [79] helps to slow down the droplets (and to evaporate the volatile excipients). An even more effective solution is to use spacer devices [4,79-87], in which the aerosol cloud can slowed down, the volatile constituents can evaporate, and any large particles will sediment out. Moreover, the patient can then inhale the remaining aerosol under optimal conditions for pulmonary delivery [4,8,56,79], that is, with a slow inspiratory flow rate. 

For aerosols in which the particle velocity is determined by the inspiratory flow rate and the particle size is not sensitive to it, it is expected that the increase in flow rate increases the upper and central airway deposition. For example, Ryan et al. [90] found that fast vital capacity inhalation resulted in a greater proportion of nebulizer aerosol depositing in the central airways than when the aerosol was inhaled slowly. However, the dependence on the inspiratory flow rate becomes more subtle when the particles have intrinsic velocity (such as droplets generated by propellant-driven metered-dose inhalers that need to be entrained into the inhaled air) or the particle size is inspiratory flow dependent (as in the case of passive dry powder inhalers). 

Following the debate surrounding sampling by inertial impaction in the early 1990s, the apparatus required for propellant-driven metered-dose inhalers and dry powder inhalers has been specified by the USP [33] and EP [147]. In addition, the FDA has issued guidelines on the methods to be employed for both pulmonary and nasal delivery products [148]. 

Figure 16.1. (A) Schematic diagram of a propellant-driven metered dose inhaler. (B) Schematic diagram of a dry powder inhaler. (C) Schematic diagram of a air-jet nebulizer.

Smyth HDC. The Influence of Formulation Variables on the Performance of Alternative Propellant-driven Metered Dose Inhalers. Adv DrugDelivRev 2003 55 807-828. 

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