Drug migration into soft gelatin capsule shells and its effect on in-vitro availability

Area of Science:

• Pharmaceutical Sciences
• Materials Science

Background:

• Soft gelatin capsules are common drug delivery systems.
• Understanding solute migration within capsules is crucial for stability and efficacy.

Purpose of the Study:

• To investigate the factors influencing solute migration from capsule contents to shells.
• To correlate solute properties with migration extent.

Main Methods:

• Analysis of capsule shells and contents for various solutes (acetomenaphthone, ephedrine, 4-hydroxybenzoic acid, phenobarbitone).
• Solvent manipulation using isopropyl myristate and 1-octanol blends.
• Monitoring solute distribution during manufacturing and storage.

Main Results:

• Solute uptake by shells increased with aqueous solubility.
• No acetomenaphthone (negligible solubility) migrated, while 92% of 4-hydroxybenzoic acid (high solubility) migrated.
• Solute migration is predictable using aqueous solubility and partition coefficients.
• Most migration occurred during drying stages (67% basket drying, 92% tray drying).

Conclusions:

• Aqueous solubility is the primary driver of solute migration into soft gelatin capsule shells.
• Manufacturing processes, particularly drying, significantly impact solute distribution.
• Predictive models can be developed based on solute physicochemical properties and process parameters.