Benzocaine diffusion from polyethylene glycol through human stratum corneum

Area of Science:

• Dermatology
• Pharmaceutics
• Materials Science

Background:

• Benzocaine is a topical anesthetic commonly formulated in ointments.
• Polyethylene glycol (PEG) is a versatile excipient used in various pharmaceutical formulations.
• Understanding drug diffusion through the stratum corneum is crucial for topical drug delivery.

Purpose of the Study:

• To investigate the diffusion, penetration, and surface effects of benzocaine in different polyethylene glycol (PEG) ointment bases.
• To elucidate the influence of PEG molecular weight on benzocaine's stratum corneum permeation.
• To examine the morphological changes induced by benzocaine and PEG on the human stratum corneum.

Main Methods:

• In vitro diffusion studies using human stratum corneum as a barrier in a diffusion cell.
• Quantification of benzocaine concentration in the receiving compartment over time.
• Scanning electron microscopy (SEM) to visualize surface morphology changes.
• Thermal analysis to assess drug-excipient interactions.

Main Results:

• Benzocaine diffusion was reduced when higher concentrations of lower molecular weight PEG were present in the ointment base.
• SEM revealed that both benzocaine and PEG significantly altered the surface structure of the stratum corneum.
• Thermal analysis confirmed that benzocaine is soluble in polyethylene glycol.

Conclusions:

• The composition of polyethylene glycol ointment bases, particularly the proportion of lower molecular weight fractions, critically affects benzocaine diffusion through the stratum corneum.
• Benzocaine and polyethylene glycol interact with and modify the stratum corneum surface, potentially influencing drug penetration pathways.
• Benzocaine's solubility in PEG suggests a direct interaction relevant to its formulation and delivery characteristics.