Selection of Surfactants, Co-surfactants, and Emulsifying agents in Nanosuspensions

Abstract

Majority of the drugs and newly discovered pharmaceutical entities are hydrophobic and/or lyophobic in nature and have an inconsistent absorption rate, lowered bioavailability, and reduced stability. Nanosuspensions have emerged as a modern solution to these issues and it has facilitated the production of new therapeutic options along with other utilities as well. Nanosuspensions are biphasic colloid dispersions that have a submicron size (i.e. the particle size is usually less than one micron with an average particle size ranging between 200 and 600 nm), target the cells and tissues, and can show sustained stabilization over an extended period of time. Thus, it has evolved with time into an ideal advanced drug delivery system with an admirable efficiency. Although there are multiple components of a nanosuspension, the ones that really stand out are surfactants, co-surfactants, and emulsifying agents, mainly due to their functional contribution to the formulation and stabilization. Surfactants are the surface-active agents that act by reducing the interfacial tension of the colloidal dispersion medium that prevents the nanosuspension from aggregating and settling down. It is amphiphilic in nature, consisting of a hydrophilic head and a hydrophobic tail. It increases the bioavailability of the drug while stabilizing the nanosuspension and improving its dispersibility, thus maintaining the particle size and colloidal structure at all time. Surfactants are ably aided by co-surfactants as well that have similar chemical properties and can bring down the interfacial tension to a more optimal level. Emulsifying agents also have a similar contribution to the stabilization and bioavailability of the nanosuspension, although its functionality is largely dependent on maintaining smaller proportion of particle size and preventing them from coalescing. Although all the three components have their fair share of advantages and challenges, the former outweighs the latter significantly. Therefore, a thorough understanding of the roles of each of them in a nanosuspension can go a long way in revolutionizing the nano-industry, especially in pharmacotherapeutics.