Surface Active Agents and Their Application in Pharmacy

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Introduction

Surface-active agent(surfactants) is a substance when added to a liquid, reduces its surface tension, thereby increasing its spreading and wetting properties. Surfactants are often classified according to their use. But, this is not very useful due to many surfactants have several uses, and confusions may arise from that. The most accepted and scientifically sound classification of surfactants is based on their dissociation and solubility in water. The critical micelle concentration is the concentration of the surfactants in a bulk phase, above which aggregates of molecules called micelles .

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Surfactants are used for pharmaceutical products poorly soluble in water to reduce the interfacial tension between the medium and The drug in order to increase solubility of drugs. As solubilizers, surfactants are used in drinks to dissolve herbal medicinal ingredients, vitamin E, and other oil ingredients. We will discuss what is the surfactants ? , critical micelle concentration , Hydrophilic-Lipophilic Balance and the pharmaceutical applications of surfactants.

Surface-active Agent

Surface-active agent also called surfactant which is able to reduce the interfacial tension between oil and water and help to alter the wetting phase behavior.

Surfactant consists of two different functional groups in the same molecule. This structure with two opposing functions is called an amphiphilic structure. The molecules of the surfactants have an alkyl chain with 8:22 carbons. This chain is known as a hydrophobic group, which does not tend to water. The molecules of the surfactants also have a functional group called the hydrophilic group that tend to water.

Types of Surfactants

Surfactants are classified into ionic surfactants and nonionic surfactants.

Ionic surfactants are subclassified into:

anionic surfactants where the hydrophilic group dissociates into anions in aqueous solutions
cationic surfactants which dissociate into cations
amphoteric surfactants which dissociate into anions and cations which depends on the PH.

Nonionic surfactants do not dissociate into ions in aqueous solutions, and they are subclassified depending on the type of their hydrophilic group . Common hydrophilic groups of ionic surfactants are (-COO) (-OSO3) (-SO3) (-NR2CH2COO) (-N(CH3)2C3H6SO3) and (-R4N). Surfactants are also classified depending on their solubility, such as (a),hydrophilic surfactants which are soluble in Water (b) hydrophobic (lipophilic) surfactants which are soluble in lipids. Ionic surfactants are hydrophilic Surfactants on another hand nonionic surfactants can be hydrophilic or lipophilic it’s depending on the balance between the hydrophilic group’s capacity of attracting water and the lipophilic group’s capacity of attracting oil.

Critical Micelle Concentration (CMC)

Critical micelle concentration (CMC) is the value at which the solution Property of the molecule shows an abrupt change. Active surface ions or molecules in solution are connected to form larger units at this concentration. These associated units are called micelle, and generally, the first aggregates formed are approximately spherical. Every molecule with surfactant has a characteristic CMC value. At a given temperature each surfactant molecules has a characteristic CMC value and other surface active substances.

Hydrophilic-Lipophilic Balance (HLB)

The term Hydrophilic-Lipophilic balance (HLB), first proposed by Clayton is referring to the balance in size and strength between the hydrophilic and Hydrophobic in surfactant molecule. In other words, It’s the relative efficacy of the hydrophilic portion of the surfactant molecule to its lipophilic portion of the same molecule. HLB was first suggested By Griffin and currently several formulas to calculate HLB have been reported. given that HLB indicates the characteristics of non- ionic surfactants, it is customarily used as an indicator for choosing a surfactant for specific applications like emulsifiers or cleansers. However, since HLB is merely experience based predictor , it can be used as a guide for selecting s surfactant for an application but this isn’t sufficient in the creation of formulations and can lead to several challenges. Find out the characteristics of surfactants efficiently and quickly is vital in formulation development. Besides the HLB, there are two indicators which display these characteristics subjectively: the cloud point for non-ionic surfactants and the Kraft point for ionic surfactants .

HLB Calculation

Given: 45 g of Span 80 (HLB 4.3) and 55 g of Tween 80 (HLB 15).

The calculation for the HLB value of the mixture is as follows:

%A = 100 (X – HLB Span80) / (HLB Tween80 – HLB Span80)

Substituting the given values:

55 = 100 (X – 4.3) / (15 – 4.3)

Solving for X gives an HLB value of 10.18.

Application of Surfactants in Pharmacy

Modern surfactants have to meet consumer requirements in mildness and naturalness. Synthetic surfactants have factors such as low price, easy availability, and expanded areas of use, while bio-based surfactants factors are their ecological advantages, the availability of a wide variety of substrates, and increased knowledge of eco-friendly goods. Surfactants are commonly used in upstream and downstream processing and drug formulation. General use surfactants improve i) the percutaneous absorption and solubility of medical products and pharmaceutical agents, ii) increase the hydrophilicity of the oil bases used in ointments and patches.. Surfactants are widely used in formulations of pharmaceutical proteins to fight for interfaces which could allow the API to unfold and accumulate. Non-ionic surfactant application is considered to be widespread in protein formulations.

Natural surfactants are derived from sorbitol, saccharose, glucose and plant oils such as coconut or palm kernel carbohydrates. The lung surfactant includes phospholipids, making it easier for oxygen to reach the lining of the lung surface and move into the blood.

Conclusion

Surfactants are substances to decrease the interfacial tension between two phases. These are usually used in pharmaceutical Products to increase the solubility of drugs, the dissolving of herbal medicinal materials and Vitamin E in drinks. Surfactants also used in dental, oral, sublingual (under Tongue) for the formulation of ointments, creams, gels, patches, tapes, and liquids, as well as Dissolve, disperse, emulsify, and solubilize medicinal ingredients were found Safe and ingestible.