Factors affecting total and "respirable" dose delivered by a salbutamol metered dose inhaler.

Abstract

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...

Inhalation Therapy in Patients Receiving Mechanical Ventilation: An Update

“…However, the failure to shake a pMDI canister that has been standing overnight may decrease total emitted and respirable dose by as much 25 and 35%, respectively, because the drugs in pMDI formulations tend to separate from their propellants during this interval. (25) Therefore, it is good practice to prime a pMDI before first use and if it has not been actuated for more than 24 h. pMDIs should be shaken before the first actuation of each dose (series of actuations) administered. However, once shaken, up to eight actuations from a pMDI can be sequentially administered within a short time period without a reduction in emitted dose.…”

Evaluation of asthma control, parents’ quality of life and preference between AeroChamber Plus and AeroChamber Plus Flow-Vu spacers in young children with asthma

“…Despite the availability of many inhaler devices with various design and formulation, the pressurised metered dose inhaler (pMDI) is still widely prescribed by the healthcare providers [5], [6]. The success of the pMDI therapy, therefore, depends not only on the therapeutic active ingredients of the pMDI, but also crucially on the correct inhaler technique used by the patients themselves [5], [7], [8], [9].…”

Washing plastic spacers in household detergent reduces electrostatic charge and greatly improves delivery

“…The use of pressurized metered-dose inhalers (pMDIs) is associated with a number of problems, including high oropharyngeal deposition and co-ordination difficulties [1]. Holding chambers (spacers) have been designed to overcome these problems [2±5], and are widely used in aerosol therapy for both adults and children.…”