AquaPolish MS: HPMC Moisture Barrier Coating for Hygroscopic Actives

A ready-to-use HPMC film coating improved moisture sealing over a standard HPMC formulation and performed similarly to a PVA-based coating after 96 hours, per a BIOGRUND case study.

Vitamin C is one example of a hygroscopic active: exposed to humidity it oxidizes quickly, and protective packaging does not fully prevent moisture ingress. Polyvinyl alcohol (PVA) coatings seal well but are not accepted in every market, while common hypromellose (HPMC) coatings often fall short as a moisture barrier. BIOGRUND reports that AquaPolish MS, a ready-to-use aqueous HPMC premix, achieves reliable moisture sealing and an improved sealing effect compared with a standard HPMC formulation.

The challenge

• Moisture and oxygen sensitivity: Vitamin C (ascorbic acid) is highly sensitive to moisture and oxygen, oxidizing quickly to dehydroascorbic acid and other degradation products when exposed to humidity.
• Packaging is not enough: Even with protective packaging such as Alu/Alu blisters, moisture ingress cannot be fully prevented, so a moisture-protective film coating is essential.
• PVA is not universally accepted: PVA-based coatings offer excellent moisture protection properties, but are not accepted in certain markets, limiting global applicability.
• Aqueous coatings carry a stability risk: Moisture retention can cause stability issues, so an aqueous coating needs faster application and drying.
• Standard HPMC often falls short: Common HPMC-based coatings often do not provide a sufficient moisture barrier.

How it was tested

• Moisture absorption was determined by differential weighing: tablets were weighed before entering the climatic chamber, then every 24 hours.
• Chamber conditions were 40 degrees C and 75 percent relative humidity.
• The chart covers placebo tablets coated with different AquaPolish film coating systems at a 4 percent weight gain.
• Performance is reported against a standard HPMC film coating and a PVA-based coating.

The solution

AquaPolish MS is an aqueous HPMC-based film coating supplied as a ready-to-use premix. BIOGRUND states that it insulates the tablet core sufficiently to protect it from external environmental influences, while undesirable interactions with the active are avoided and stability and bioavailability are not impaired. It is offered with or free of titanium dioxide (TiO2), with color matching available.

Results

BIOGRUND reports that tablets coated with 4 percent (weight gain) standard HPMC film coating provide adequate protection against moisture, and that AquaPolish MS coated tablets provide an improved moisture sealing effect compared with the standard HPMC formulation. After 96 hours of storage time, AquaPolish MS coated tablets performed similarly to a PVA-based film coating. The case study also shows uncoated Vitamin C tablets undergoing the typical degradation due to hydrolysis, next to tablets coated with 4 percent AquaPolish MS showing no reaction with the active on stability.

See the full case study on HPMC film as moisture protective coating for hygroscopic actives here:

HPMC film as moisture protective coating for hygroscopic actives

(click the picture to download the document)

Source: BIOGRUND, case study HPMC film as moisture protective coating for hygroscopic actives

Sources

1. BIOGRUND, HPMC film as moisture protective coating for hygroscopic actives, case study, 2025.

This article is for informational purposes for pharmaceutical industry professionals and does not constitute regulatory advice. Always refer to the current pharmacopoeial monograph, the supplier’s current technical data sheet, and applicable regulatory guidance for your dosage form, route of administration, and market. Pharma Excipients International AG is not a manufacturer of the excipients discussed.

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