How can HPMC prevent drug absorption and deterioration during drug preparation storage? ​

Hydroxypropyl methylcellulose (HPMC)In the storage of drug preparations, the main methods are to reduce the contact between the preparation and external moisture from the root through its physical barrier properties, hydrophilic regulation ability, and structural stability, while inhibiting the degradation reaction of drug components, thereby achieving the effect of preventing drug absorption and deterioration. The specific mechanism of action and application method are as follows:

1、 Build a physical barrier to isolate external moisture

HPMC is a water-soluble polymer that can form a dense protective layer in formulations through film formation, bonding, and other methods to block the path of moisture invasion.

As a film coating material

This is one of the core application methods of HPMC. HPMC is prepared into a coating solution (usually with appropriate plasticizers such as glycerin and propylene glycol added), which is covered on the surface of tablets and granules through the spray coating process, and dried to form a continuous and dense film.

This film is insoluble in water but can swell in water (stomach soluble HPMC). During storage, it can effectively block water vapor and oxygen from entering the interior of the formulation, avoiding the active ingredients of the drug from clumping, dissolving, or undergoing chemical changes due to moisture absorption.

Compared to traditional coating materials, the film formed by HPMC has good flexibility, is less prone to cracking, and has a more durable barrier effect, especially suitable for humidity sensitive drugs such as vitamins and antibiotics.

Preparation of particles as adhesive

In wet granulation, HPMC aqueous solution can be used as a binder to tightly bond drug powder and excipients to form uniform particles.

After drying, a layer of HPMC film will adhere to the surface of the particles, filling the gaps between the particles and reducing the porosity of the formulation - which is the main channel for moisture to enter. The decrease in porosity can directly reduce the contact area between the drug and moisture, and slow down the moisture absorption rate.

2、 Adjust the hydrophilicity of the formulation and control the internal moisture distribution

HPMC has moderate hydrophilicity and water absorption swelling properties, which can prevent drug deterioration due to excessive local moisture by adjusting the internal moisture state of the formulation.

Selective adsorption of moisture to avoid direct drug absorption

The hydroxypropyl group and methoxy group on the HPMC molecular chain are hydrophilic. In the environment with high humidity, they will preferentially absorb the water in the environment and swell, forming a hydrated gel layer.

This "preferential water absorption" characteristic can reduce the contact between the active ingredients of drugs and water, especially for drugs that are prone to moisture absorption (such as salt drugs and traditional Chinese medicine extracts), which can effectively prevent them from experiencing deliquescence, crystal transformation, or reduced efficacy due to water absorption.

Inhibit water migration and maintain formulation stability

In multi-component formulations, the differences in moisture absorption of different excipients may cause water migration within the formulation, leading to changes in local drug concentration or degradation.

HPMCThe formed network structure can fix the trace water inside the formulation, prevent water migration, maintain the overall water uniformity of the formulation, and avoid deterioration reactions such as drug oxidation and hydrolysis accelerated by local high humidity environment.

3、 Stabilize drug structure and inhibit degradation reactions

In addition to its anti hygroscopic effect, HPMC can also enhance the chemical stability of drugs by interacting with drug molecules, indirectly preventing drug spoilage.

Packaging and protection of drug molecules

In preparations (such as suspensions and gel), HPMC molecular chains can combine with drug molecules through hydrogen bonding to wrap drug particles in their reticular structures, forming microencapsulated or colloidal dispersion systems.

This wrapping effect can isolate the drug from external degradation factors such as oxygen and light, while reducing the interaction between drug molecules and avoiding the decrease in efficacy caused by aggregation and crystallization.

Adjust pH microenvironment to slow down hydrolysis reaction

The hydrolysis reaction of some drugs is closely related to the environmental pH (such as esters and amides). HPMC itself is neutral and has a certain buffering capacity, which can form a stable pH microenvironment around drug particles, avoiding accelerated drug hydrolysis due to external pH fluctuations or the influence of excipient acidity and alkalinity.

4、 Precautions for using HPMC in preparation storage

Choose the appropriate model of HPMC

There are significant differences in the performance of HPMC with different viscosities and degrees of substitution: high viscosity HPMC has stronger film-forming and barrier properties, making it suitable for humidity sensitive drugs; Low viscosity HPMC has good fluidity and is more suitable as an adhesive. Select the corresponding model based on the characteristics of the drug.

Control the amount of HPMC added

If the amount added is insufficient, an effective barrier cannot be formed; Excessive addition may slow down the dissolution rate of the formulation and affect the bioavailability of the drug. The optimal ratio needs to be determined through experiments.

Collaborative control of storage environment

HPMCThe anti hygroscopic effect is auxiliary, and the storage of the formulation still needs to be accompanied by dry, sealed, and low-temperature conditions to avoid long-term exposure to high humidity (relative humidity>60%) environment, in order to prevent the drug from absorbing moisture and deteriorating.