Application of Surfactants in Pharmaceutical Formulations
Surfactant is a very widely used additive in the prescription of pharmaceutical preparations. It consists of lipophilic and hydrophilic groups, which are both hydrophilic and lipophilic, and can significantly reduce the surface tension of the liquid and increase the solubility of the drug. Image How to increase the solubility of drugs?
Hydrophilic and Lipophilic Equilibrium Value of Surfactants
The index used to indicate the hydrophilic or lipophilic ability of surfactants is the hydrophilic-lipophilic balance value, also known as HLB value.
According to general experience, the HLB value of a surfactant is limited to the range of 0 to 40, the higher the HLB value, the greater the hydrophilicity of the surfactant; the lower the HLB value, the greater the lipophilicity of the surfactant. If the hydrophilic or lipophilic ability is too large, the surfactant is easily soluble in water or oil.
HLB value is closely related to the application of surfactants.
For example, the HLB value of Tween 60 is 14.9, and according to the table, it can be used as an emulsifier, solubilizer and decontaminant for oil-in-water type.
Application of surfactants in pharmaceutical preparations
01
As solubilizer
The solubility of some water-insoluble or slightly soluble substances in surfactant micellar solutions can be significantly increased, and this effect is called solubilization. The surfactant acting as solubilizer is called solubilizer. The solubilized substance is called solubilizer.
For example, the solubility of cresol in water is only about 2%, whereas in a soap solution it increases to 50%.
Some volatile oils, fat-soluble vitamins, steroid hormones and other difficult-to-solve drugs can be solubilized in this way to increase their concentration and form a clear solution.
02
As an emulsifier
We all have this life experience, if you add oil in water, oil and water will be divided into two layers, this is because the oil and water are different in nature and immiscible, and surfactants can make one of the liquid, with tiny droplets evenly dispersed in the immiscible other liquid to form an emulsion, this effect is called emulsification. The surfactant that acts as an emulsifier is called an emulsifier.
The HLB value of the surfactant can determine the type of emulsion. Usually, surfactants with HLB values between 3 and 8 are used as water-in-oil emulsifiers to form water-in-oil emulsions; surfactants with HLB values between 8 and 16 are used as oil-in-water emulsifiers to form oil-in-water emulsions.
03
As wetting agent
Reduce the interfacial tension between hydrophobic solid drug and wetting liquid, so that the liquid can adhere to the solid surface. Surfactants with HLB values in the range of 7~9 are generally used as wetting agents.
04
As foaming agent and antifoaming agent
Foaming agent is a surfactant that can produce foam, generally with strong hydrophilicity and high HLB value, can reduce the surface tension of the liquid, so that the foam tends to stabilize. Foam formation is easy to make the drug application site evenly dispersed and not easy to lose. Foaming agents are generally used in dosage forms for dermal, luminal and mucosal administration.
Defoamer is a surfactant used to eliminate foam, usually with strong lipophilicity and HLB value of 1~3. Certain herbal leachate or polymer compound solution, which itself contains surfactant or surface-active substances, will produce a large number of stable foams when stirring vigorously or evaporating and concentrating, hindering the operation, which can be overcome by adding defoamer.
05
As a disinfectant and bactericide
Surfactants can interact strongly with bacterial biofilm proteins and denature or destroy them, e.g. cresol soap, benzalkonium bromide, etc. can be used as disinfectants. According to the concentration used, it can generally be used to
