Continuing patient care with metered-dose inhalers

Abstract

International guidelines recommend inhaled therapy over oral therapy for asthma because of greater efficacy and safety. Metered-dose inhalers (MDIs) are the delivery system of choice for the majority of patients with asthma. They have been well tried and tested and proven to be safe, reliably delivering a reproducible and precise dose, and account for 85% of the 400 million inhalers currently sold worldwide. Current products using chlorofluorocarbon (CFC) 11/12 as the propellant are being reformulated. Under the Montreal Protocol, CFCs are to be phased out worldwide, though MDIs have been granted temporary exemption, thus far until 1997. Two propellants, hydrofluoroalkane (HFA) 134a and 227, have been identified by the pharmaceutical industry to replace CFCs. However, they have different properties and reformulation has been difficult in relation to surfactants, valves and elastomeric seals. The manufacturing process has been re-engineered to take place at high pressure, because at normal pressure HFA134a is a gas, in contrast with CFC 11 which is a liquid at room temperature. Glaxo has carried out an extensive toxicological assessment of HFA134a and thorough clinical testing has shown it to be well tolerated. To date they have carried out safety and efficacy testing on reformulations of salbutamol, salmeterol and fluticasone propionate (FP). Single-dose studies of salbutamol, 200 micrograms, with HFA134a have been shown to provide equivalent protection against bronchial provocation by histamine in both adults and children with asthma when compared with the currently available CFC preparations. In a subsequent 4-week study, both formulations had similar effects on morning peak flow and the patients believed that the two preparations were equivalent.