In the field of medicine, gel plaster, as a topical preparation, has attracted extensive attention due to its unique efficacy and convenience. However, the preparation process and mechanism of gel plaster make it a complex preparation. This article will discuss the complexity of gel plaster and reveal its scientific principles and clinical advantages.

Gel paste is a kind of paste made by mixing raw materials and appropriate hydrophilic matrix, and then coating it on the backing material. It belongs to complex preparations and exerts therapeutic effects through local administration. The remarkable feature of gel plaster is that it often needs more excipients to form corresponding dosage forms. These excipients include skeleton materials, thickening agents, pH regulators and other multi-component ingredients. The choice and change of its prescription and dosage forms can directly affect the effectiveness or safety of drugs. Its main components include:

The active ingredients in gel pastes are used to treat specific diseases or relieve symptoms.

It is usually composed of polymer materials (such as sodium polyacrylate, carbomer, etc.) and solvents (such as water, ethanol, etc.), used to immobilize drugs and control drug release.

Used to support patches and prevent drug leakage, common materials include non-woven fabric, polyester film, etc.

Used to protect patches from contamination before use, common materials include release paper coated with silicone oil.

The drug release of gel plaster is a complex physical and chemical process. The release of drugs from the matrix requires overcoming the physical barriers and chemical binding forces of the matrix. The composition and structure of the matrix have a significant impact on the drug release rate. For example, the molecular weight, crosslinking degree, and swelling properties of polymer materials can all affect drug release. In addition, the volatilization of solvents and the hydration of the matrix can also alter the physical state of the matrix, further affecting the release of drugs.

The absorption of drugs through the skin is a multi-step process, including penetration through the stratum corneum, diffusion through the epidermis, and absorption through the dermis. The stratum corneum is the main barrier for skin absorption, and its complex structure and lipid bilayer make it very difficult for drugs to penetrate. In order to improve the skin absorption of drugs, gel patches usually add transdermal absorption enhancers, such as azone, menthol, etc. These enhancers can alter the structure of the stratum corneum and increase the penetration of drugs. However, the type and concentration of transdermal absorption enhancers need to be precisely controlled to avoid skin irritation and allergic reactions.

The preparation process of gel plaster is very complex, involving multiple steps and fine control. The main steps include:

- Mixing of drugs with matrix: Drugs need to be evenly dispersed in the matrix to ensure uniform release. This usually requires high-speed stirring and homogenization treatment.
- Coating: Apply the mixed ointment evenly onto the backing material, and the thickness and uniformity of the coating are crucial for drug release.
- Drying: The coated patch needs to be dried under controlled conditions to remove excess solvents. Drying conditions such as temperature, humidity, and time can affect the physical state of the substrate and the stability of the drug.
- Cutting and packaging: Cut the dried plaster into appropriate sizes and package it to ensure the stability and safety of the product.

The quality control of gel paste is very strict, and multiple indicators need to be tested to ensure the safety and effectiveness of the product. The main testing indicators include:

- Drug content: Ensure that the drug content in each patch meets the standard.
- Release rate: Simulate skin absorption conditions, detect drug release rate and total amount.
- Skin irritation: Evaluate the irritation and allergic reactions of the patch on the skin through skin irritation tests.
- Microbial limit: Ensure that the product is sterile and meets microbial limit standards.

Although the preparation and use process of gel plaster is complex, it has significant advantages in clinical practice:
1. Significant local treatment effect: The drug directly acts on the lesion site, with high local drug concentration and good treatment effect.
2. Easy to use: The plaster form is easy to use and has high patient compliance.
3. Reduce systemic side effects: Drugs are absorbed through the skin, and the amount of drugs entering the systemic circulation is relatively small, reducing systemic side effects.
4. Long term effect: The drug can be continuously released, maintaining its efficacy for a longer period of time and reducing the frequency of medication.

As a complex preparation, the preparation process and mechanism of gel plaster involve many complex physical and chemical processes. Nevertheless, gel plaster has become an important external preparation due to its remarkable advantages in clinical use. In the future, with the continuous development of material science and drug delivery technology, gel plaster is expected to play a greater role in the treatment of more diseases.