Several in vitro and in vivo studies have emphasized the importance of generating a high inspiratory flow when using a dry powder inhaler. Little attention has been paid to the influence of the inspiratory flow profile on the particle size distribution contained in aerosols generated by these devices. The internal volume of a device such as the Turbuhaler is small compared with a vital capacity breath and it is possible that all the powder has been drawn from the device before peak inspiratory flow has been achieved, particularly if the time to peak inspiratory flow is prolonged. A series of experiments were performed to assess the effect of different flow profiles through the Turbuhaler, each with a peak flow of 60 1 min-1. A 400 microgram budesonide Turbuhaler was enclosed in a chamber allowing air to pass unimpeded through the dosing channels and entrainment ports. A large three-way tap was used to blow powder from the device across a Malvern Mastersizer laser particle sizer which produced a profile of the particle size distribution within the aerosol. The rate of increase in flow through the Turbuhaler was determined by the rate at which the three-way tap was turned, and recorded by means of a pneumotachograph. The rate of increase in flow was found to significantly affect the particle size-distribution within the aerosol. Failure to attain a flow of 30 1 min-1 before 150 ml of air had passed through the device resulted in the aerosol volume median diameter increasing from less than 6.6 microns to greater than 45.3 microns. These results indicate that flow during the initial part of the inspiratory effort may be important in determining the characteristics of the aerosol generated by a dry powder inhaler. With more sophisticated equipment, it might be possible to explore the relationship between flow profile and particle size distribution generated by dry powder devices in more detail.
Background -Many factors contribute to the high variability of doses delivered to the lungs of patients using metered dose inhalers (MDIs). Relatively little attention has been paid to the contribution to this variability of the way in which the MDI is handled before the inhalation manoeuvre. Instruction leaflets often recommend procedures at odds with those used for in vitro testing of the device. The standard protocol for in vitro assessment of salbutamol MDIs involves shaking the MDI vigorously for 30 seconds and wasting the first two actuations. Subsequent actuations are introduced into the testing device at five second intervals. Patient instructions do not include a recommendation to waste the first two actuations and recommend a delay of one minute between actuations. A series of experiments was performed to determine whether such differences might be important. Methods -The total and "respirable" doses delivered by a salbutamol MDI (Ventolin, Allen & Hanburys) under various conditions were assessed with a multistage liquid impinger. The quantity of drug deposited on each stage was measured by an ultraviolet spectrophotometric method. The effect on the delivered dose of not shaking the canister, not wasting the first two doses, waiting 30 seconds between actuations, and using multiple rapid actuations was assessed by comparing the results with those obtained using the standard in vitro testing protocol. Results -Compared with a standard protocol, it was found that not shaking the MDI before use reduced the total and "respirable" dose by 25-5% and 35 7%, respectively. The dose delivered when actuating the MDI at 30 second intervals was no different from that when intervals of five seconds were used. Two actuations separated by one second had no effect on the total dose but reduced the "respirable" dose by 15-8%, while four rapid actuations reduced the total and "respirable" doses by 8-2% and 18-2%, respectively. Storing the MDI stem down reduced the total and "respirable" dose delivered in the first actuation by 25 Although metered dose inhalers (MDIs) are the devices most widely used for aerosol therapy, their effectiveness is often adversely influenced by suboptimal use. Recommendations for use vary and this can cause confusion in the minds of patients wishing to use the devices optimally and in those instructing them. Hence, instructions should be as simple as possible.Protocols used by drug companies for handling MDIs during in vitro assessment of formulations frequently vary from that recommended for clinical use. A typical standard protocol when using a particle sizing device such as a multistage liquid impinger involves shaking the MDI vigorously for 30 seconds and then wasting the first two actuations. The MDI is then actuated a predetermined number of times into the particle sizing device. These actuations are separated by an interval of 5-30 seconds, depending upon the protocol being used, and the MDI is shaken between each actuation.Instructions for clinical use do not normally include w...
Although more than 20 years have passed since radioisotopes were first used to study the deposition of aerosols in the respiratory tract of children,' such studies have only recently become relatively more common.2 The reason for this lies in the widespread concern regarding the use of radioisotopes for research purposes in childhood. Indeed, this concern is such that certain journals have rejected studies, not on the basis of their scientific content, but upon the editor's view that such studies are essentially unethical. However, information obtained from such studies is becoming increasingly important as the number of expensive and potent therapeutic agents being delivered by this route increases.7The purpose of this paper is to review radiation protection and ethical issues relating to the use of radioisotopes in research projects involving children. It then goes on to discuss technical aspects relevant to those interested in designing or interpreting radiolabelled aerosol deposition studies in children.
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