When evaluating a polymer, there are four primary questions to consider.
- The first criterion is whether there is chemical incompatibility between the active ingredient and /or one of its excipients and gelatin. If one is found in preliminary testing, then the choice of HPMC is often necessary.
- Secondly, if the formulation is moisture sensitive—in which the active ingredient may degrade with exposure to moisture or hygroscopic in which water migration from the shell may occur, the lower moisture HPMC capsule may be better for stability.
- The third question is whether the formulation is sensitive to oxidation. Gelatin hard capsules have long been recognized for the ability to restrict permeation of oxygen through the shell wall. HPMC, however, allows for greater oxygen permeability. Gelatin might be the better choice unless antioxidants are added to the formula.
- Finally, the region in which the product will be marketed is an important consideration—religious and dietary implications as well as avoiding certification requirements that accompany animal-derived products may make HPMC the better choice.