Polysorbate 80, the chemical name is polyoxyethylene 20 sorbitan monooleate, is a non-ionic surfactant, has significant adaptability to different pH, and is relatively stable when coexisting with high-concentration electrolytes. The water-lipophilic balance value (HLB value) is 15. It has strong hydrophilicity and is miscible with water, methanol, ethanol, chloroform and ethyl acetate. It is widely used in injections and oral preparations as O/W (water oil-in-oil) type emulsifier, solubilizer, wetting agent.
Studies have shown that when polysorbate 80 reaches a certain critical micelle concentration, the hydrophobic parts of its molecules attract each other and combine to form micelles. The formed spheroids, the solubilized substances, combine with the micelles in different ways, thereby increasing the dissolution of the drug components, but the solubilization effect is different from the real dissolution effect.
In practical work, attention should be paid to the order of adding solubilizers. A large number of studies have shown that polysorbate 80 should be mixed with fat-soluble drugs first, preferably to be completely dissolved, and then diluted with water to dissolve well.
When the solubility of polysorbate 80 increases to a certain level, it will appear turbid, because the hydrogen bond between polysorbate 80 and water is broken. The temperature is the breaking point, and the breaking point of polysorbate 80 is 93 degrees Celsius. Due to the breaking phenomenon, the corresponding solubilized substances may be precipitated. Therefore, in actual work, care should be taken to avoid high temperature sterilization and other similar operations.
In some cases, after solubilization, the absorption of the drug is reduced, and the activity of the drug is weakened. Most of the reason is that the drug gets into the solubilizer micelle which hinders the dissolution. Typical examples are antiseptics containing phenolic hydroxyl groups, such as parabens, chlorobutanol, benzyl alcohol, quaternary ammoniums, etc., and Tween-80 can reduce their bacteriostatic power after compatibility. Even if the solution was diluted to below the CMC of polysorbate 80, the bacteriostatic activity of parabens could not be recovered. The reason is that a mixture is formed between the polyoxyethylene groups of Tween-80 and the phenolic hydroxyl groups, and the bacteriostatic agent is encapsulated in the micelles, making them inactive.