Towards sustainable pharmaceutical foams: A comparative review of propellant-containing, propellant-aided and propellant-free foams

Pharmaceutical and personal care foams used for active pharmaceutical/cosmetic ingredient delivery are attractive formulations because of their ease of application, high spreadability including over hair-bearing skin, and ability to coat body cavity surfaces. Currently developed pharmaceutical foams for topical uses are propellant-containing whereas personal care foams may be propellant-containing or propellant-free, depending on their use. The use of propellants produces an elegant dosage form and provides benefits for topical drug delivery, however they are also associated with adverse environmental impact, safety challenges and more complex formulation development and manufacturing processes. To maintain the advantages of foams as topical dosage forms, whilst improving their environmental sustainability, propellant-aided foams based on Bag-on-Valve technology and propellant-free foams, including those using novel technologies such as EcoDrive™, may potentially be developed. Foams produced using propellants and propellant-free foams differ in their design and development in terms of formulation, method of foam generation and packaging requirements. These differences affect the quality of the final foam structure and its performance. This review, firstly, describes pharmaceutical liquid foams used for topical drug delivery and then compares them with propellant-aided and propellant-free foams in terms of their method of foam generation and formulation. This comparison identifies the potential and drawbacks of these formulations for pharmaceutical applications. Through this comparative study, the potential of eliminating environmentally hazardous propellants from these pharmaceutical formulations using ecofriendly technologies such as Bag-on-Valve and EcoDrive™ for topical drug delivery applications is discussed.