Purpose: To study how water absorption is effected by capsule materials
Methods: Model compounds (magnesium chloride and sodium bromide) were selected to represent hygroscopic compounds. Each salt has a known deliquescence point at which it absorbs or desorbs moisture (32.80%RH for magnesium chloride and 57.60%RH for sodium bromide). Each salt was filled into three types of capsules: all color gelatin capsules, Vcaps+, and enteric caps. The capsules were placed on stability at 5°C, 25°C/60%RH, and 40°C/75%RH. At each time point, average capsule weight and TGA of the contents will be determined to see if any of the capsule types provided any moisture protection to the contents.
Results: Magnesium chloride capsules all showed weight gain on both weight and TGA (Figure 1). Sodium Bromide capsules showed very minor weight gain and in most cases, water detected by TGA was lost (Figure 2). All water losses were confirmed by mass spectrometry.
Conclusion: With testing ongoing, magnesium chloride filled capsules may be used to track moisture uptake over time, but sodium bromide, with its higher deliquescence point is desorbing all moisture readily at longer time points. At early time points (up to 3 months), gelatin all color capsules appear to have lower moisture uptake than either the Vcaps+ or the enteric caps.
Mark Cappucci– Team Lead, Preformulations, Lonza, Tampa, Florida