Drug-surfactant-propellant interactions in HFA-formulations

Area of Science:

• Pharmaceutical Sciences
• Chemical Engineering
• Materials Science

Background:

• The transition from chlorofluorocarbon (CFC) to hydrofluoroalkane (HFA) propellants is mandated for metered dose inhalers (MDIs).
• Conventional surfactants soluble in CFCs are insoluble in HFA 134a and HFA 227ea, necessitating formulation adjustments.
• HFAs, while having similar physical properties to CFCs, possess increased polarity, impacting drug solubility and suspension stability.

Purpose of the Study:

• To provide an overview of the current state of the art in formulating pressurized metered dose inhalers (MDIs) with hydrofluoroalkane (HFA) propellants.
• To highlight the challenges faced by formulators in adapting to HFA propellants.
• To discuss strategies for stabilizing HFA-based MDI formulations.

Main Methods:

• Review of scientific literature and technical developments in MDI formulation.
• Analysis of surfactant solubility in HFA propellants.
• Discussion of co-solvent strategies for HFA-based MDIs.
• Consideration of drug substance properties and container interactions.

Main Results:

• Conventional surfactants are largely insoluble in HFA 134a and HFA 227ea without co-solvents.
• Alternative surfactants or co-solvent systems are required for stable HFA-based suspension MDIs.
• Challenges include patent complexities, empirical formulation science, and avoiding drug crystallization or adhesion.
• Drug dissolution using co-solvents is a viable alternative to suspension stabilization for certain compounds.

Conclusions:

• Formulating stable pressurized metered dose inhalers with HFA propellants presents significant scientific and technical hurdles.
• The choice between alternative surfactants and co-solvents depends on drug properties, patent considerations, and empirical data.
• Further research is needed to develop predictive models and overcome formulation challenges in the HFA era of MDIs.