Liquid Filling In Hard Gelatin Capsules — Preliminary Steps

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For more than 20 years, the liquid or semi-solid filling of hard gelatin capsules have been routinely performed by the pharmaceutical industry. Among the various aspects of this technique, the selection of the excipients or fills to be used remains a key step of the development process. Preliminary steps to be followed to identify suitable formulations are recommended:

• Determination of the water exchange and control of visual aspect
• Control of brittleness potential
• Accelerated stability testing

Determination of the water exchange and control of visual aspect
Gelatin behaves as a hydrophilic polymer and as such its water content may vary depending upon the storage conditions. Equilibrium moisture, sorption - desorption isotherms have been described by many authors. Depending on the previous moisture/ drying history the water equilibrium may be described by the following hysteresis curve. As long as the gelatin water content remains in the range 11 to 16 %, no significant effect has to be expected on capsules brittleness potential.

Another aspect of the gelatin film which has to be considered is its water vapour exchange. As any film, the water vapour transfer can be determined for a gelatin film. Internal studies have demonstrated that above a film thickness of 70 µm this phenomenon is constant. Our understanding is that this phenomenon is mainly driven by water sorption/desorption mechanism at the film surfaces. The transfer of the water vapour within the film (above 70 µm thickness) is not a limiting factor.

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