Drugs are one of the powerful weapons in the struggle of humans against diseases. In order to make full use of the efficacy of drugs and for patients to be able to use them conveniently, drugs need to be made into certain forms, such as powders, oral liquids, solutions, preparations, pills, capsules, injections, plasters, etc., commonly known as preparations. Suspensions are one of the more well-known types of drugs, especially some pediatric drugs often use suspension forms.

1. What aspects are related to the reliability of suspensions

1. Particle ground settlement

According to the ground settlement equation set, the larger the particle radius, the lower the viscosity of the substance, and the faster the settling velocity. To maintain it for a long time, the particle radius should be reduced or the viscosity of the suspending agent should be increased;

2. Concentration polarization and gel layer

The double layer and gel layer can maintain the repulsive force between particles, which is beneficial to stability. If the potential difference of the double layer decreases or the gel layer is destroyed, particles will precipitate. Electrolyte solutions are very easy to destroy the potential difference and gel layer;

3. Inclined plate sedimentation tank and reverse inclined plate sedimentation tank

Moderately reducing the potential difference, particles produce loose aggregates, which is beneficial to the stability of the suspension. Substances that can produce inclined plate sedimentation tanks are coagulants;

4. Crystallization

Crystallization of particles during storage, development of crystals, and precipitation occur;

5. Temperature of the dispersing medium

Reducing temperature weakens Brownian motion and reduces reliability. Therefore, it is necessary to maintain a suitable temperature.

What is a suspension?

1. Suspensions refer to non-homogeneous liquid drug preparations formed by dispersing poorly soluble solid drugs in suspending agents. Suspensions belong to the coarse dispersion system, with the particle size of the dispersing medium generally in the range of 0.5~10μm, but the particle size of the aggregates can be as small as 0.1μm and as large as 50μm. The most commonly used suspending agents are mostly water, but also edible oils.

2. Most suspensions are liquid dosage forms, but the current edition of the Chinese Pharmacopoeia has dry suspensions in the second part of personal collections. It is made into a powdered or granular drug preparation according to the provisions of suspensions, which can be quickly dispersed into a suspension by adding water when used. This is beneficial to handling the reliability issues of suspensions throughout the storage process. Suspensions are present in various dosage forms such as solutions, ointments, lavages, injections, aerosols, creams, and suppositories.

3. Suspensions have critical physical reliability issues. The particle dispersion in suspensions is large, causing the suspended particles to have a high surface activation energy and be in an unstable state. Suspensions of hydrophobic drugs have greater reliability issues than those of hydrophilic drugs.