INTRODUCTION

Foams are a dispersion of gas in a liquid or a semisolid continuous phase wherein the liquid or semisolid contains the drug substance and suitable excipients. Typical foam dosage forms include aqueous or nonaqueous carriers, foam structuring agents, surfactants, and propellants (for pressurized systems). Foams are produced by mechanical means or via interaction of propellant (vapor or gas) and the formulation under pressure. Foams dispensed from nonpressurized containers use mechanical forces allowing the mixing of the formulation and air, resulting in foam generation. Foams dispensed from pressurized containers use propellant present in gas phase to increase pressure inside the container. When the nozzle of the actuator is opened, the liquid phase containing a dispersed vapor or gas is emitted through an actuator. As a result, a foam is generated.