Some problems that may affect the formulation and composition of suppositories
There are many problems that face the formulation of suppositories and affect them greatly. For example, water is used as a solvent for medicines, but with suppositories, water may increase the chance of oxidation of fats used in making suppositories. We will mention some problems that affect the formulation of suppositories, including:
1- Water in suppositories:
Water accelerates the oxidation process of the fats that make up the suppositories.
The ingredients inside the suppository can interact with each other in the presence of water.
If the water evaporates, the solute crystallizes.
When mixing water with the components of the suppositories, the water may be contaminated with bacteria or fungi, so a bacteriostatic agent such as parabens must be added.
2- Hygroscopicity:
Gelatin and polyethylene glycol suppositories lost moisture by evaporation in dry climates and moisture absorption in high humidity conditions.
3- Brittleness:
Suppositories with a synthetic base with a high degree of hydrogenation and a higher content of stearates at room temperature may be more fragile. On the other hand, suppositories with a natural base such as cocoa butter do not break and are more flexible, so they are less fragile, to address the problem of fragility in suppositories with an artificial base it is recommended to add a small amount of Tween 80 or castor oil.
4- Incompatibility between the components of the suppositories:
Polyethylene glycol (PEG )bases are incompatible with silver salt, tannic acid, aminopyrine, quinine, ichthyol, aspirin, benzoic wine and sulfonamides.
Many chemicals tend to crystallize from polyethylene glycol (PEG), such as: camphor, sodium sarbital and salicylic acid.
The high concentration of salicylic acid dilutes polyethylene glycol to an ointment-like formula and aspirin complexes with polyethylene glycol (PEG).
Fatty bases with large hydroxyl values may react with acidic components.
5- Viscosity:
The viscosity of the suppository is important in the process of dissolving the suppository. Low viscosity suppositories affect the process of dissolving the suppository in the rectum. For example, the cocoa butter base has low viscosity compared to PEG and glycerinated gelatin. Therefore, this problem must be addressed to avoid the sedimentation of suspended particles through:
Use a base with a narrower melting range that is closer to body temperature.
Addition of 2% aluminum stearate monostearate to increase viscosity and maintain homogeneous suspension of insoluble materials.
Adding stearyl, cetyl, myristyl alcohols, or stearic acid to the suppository ingredients to improve the consistency of suppositories.
6- Rancidity and Antioxidant:
Rancidity results from the spontaneous oxidation and subsequent decomposition of unsaturated fats into low and medium molecular weight saturated and unsaturated aldehydes, ketones and acids, which have a strong unpleasant odor.