A novel formulation technique for metered dose inhaler (MDI) suspensions

Abstract

Metered dose inhalers (MDIs) are a widely used dosage form for pulmonary delivery of anti-asthmatic drugs. However, with the phase-out of chlorofluorocarbon (CFC) propellants and need to switch to the alternative pharmaceutically approved hydrofluoroalkane (HFA) propellants, the MDI formulator was faced with several technical challenges. Product components such as valves and elastomers needed to re-designed, and, due to the limited solubility of the commonly used surfactants in the HFA propellants, novel surfactants were developed or co-solvents were used to bring the conventional surfactants into solution. This paper describes a novel formulation approach for HFA based metered-dose inhalers. A physically stable micro-suspension of the model drug, budesonide, was formulated by an in situ-precipitation process using a hydrophilic stabilizer in the propellant system. A network-like structure of the precipitated drug and excipient was formed and resulted in physically stable suspensions in which the solid phase remained suspended in the propellant system for several weeks. Through life dose uniformity testing of MDI units containing formulations of budesonide produced by the novel process, was consistent and within the limits specified by the FDA draft guidance on metered dose inhalers. The fine particle fraction of the budesonide formulations showed a dependence on formulation composition and aerosol hardware (canister and actuator) illustrating flexibility in optimizing the product using this novel in situ formulation technique.