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Oil-in-Water Nanosized Emulsions for Drug Delivery and Targeting. Tamilvanan ShunmugaperumalЧитать онлайн книгу.

Oil-in-Water Nanosized Emulsions for Drug Delivery and Targeting - Tamilvanan  Shunmugaperumal


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based on size are often inconsistent and the upper end of the nanoscale at 100 nm is an arbitrary cut‐off (Boverhof et al. 2015). Thus, the 100‐nm limit is often considered constraining and, according to a more‐inclusive definition, particles <1,000 nm in each dimension (submicron particles) is designated as NPs (Keck and Müller 2006). The latter more‐inclusive definition is particularly applicable in the pharmaceutical field since the particle size in the nanometer range can lead to increased dissolution rates because of the increase in surface area and increased saturation solubility (Junghanns and Müller 2008). In this respect, the generation of nanometer range particles from the API molecule itself is coming under NPs with a nomenclature of API nanocrystals or API nanosuspensions. On the other hand, encapsulating the API into a preformed or in situ forming nanosized API delivery carrier is also grouped under NPs. Now the question will arise, at an industrial environment, which type of API is going for API nanocrystals/nanosuspensions formation and which type of API needs to go as cargo in a nanosized carrier? To clarify this confusion, the following discussion is devoted wherein the poorly soluble API is grouped into two categories.

       1.1.1.1. Poorly Water‐Soluble Grease Ball and Brick Dust Molecules

      Hydrophobic APIs have a limited capacity to interact with the water phase, in accordance with “similia similibus solvuntur” (like dissolves like), and these APIs are solubility‐limited by poor hydration. The poorly soluble APIs restricted in solubility by poor hydration are described in the popular scientific jargon as “grease ball” molecules, due to their high hydrophobicity and lack of interaction with water. Although they possess poor water solubility (insolubility is probably due to the salvation extreme), the grease ball molecules are easily soluble to lipids or oils and therefore these molecules can plausibly be formulated into lipid‐or oil‐based formulations. In contrast, the brick dust molecules are poorly soluble due to crystal packing interactions being insoluble to both aqueous solvents and lipids or oils. So, the aqueous solubility of brick dust molecules could be enhanced by the formation of amorphous materials or particle size decrease, e.g., nanocrystallization. Thus, formulating APIs as nanocrystals should be mainly used as a solubility enhancement formulation approach to brick dust molecules rather than to grease balls.

      In other words, Yalkowsky and coworkers established the General Solubility Equation (GSE), in which the solubility of a compound is expressed as a function of the melting point (Tm) and its lipophilicity (in the form of the octanol‐water partition coefficient, log Ko/w or simply the log P value) (Jain and Yalkowsky 2001). The GSE states the following relationship:

      where S0 is the intrinsic solubility, i.e., the solubility of the non‐ionised (neutral species).

      Extracted from Bergström and Larsson (2018).

Grease Ball API Brick Dust API
Highly lipophilic compound with high log P (>3 or 4) and a low melting point (<200°C) Compound with high log P (<2) and high melting point (>200°C)
Poorly soluble compounds restricted in solubility by poor hydration are described as grease ball molecule Compound with strong intermolecular bonds and/or complex interaction patterns with large number of interaction points between the molecules in the crystal lattice which often shows a limited capacity to dissociate from the solid form. This type of compounds are called as brick dust (stone‐like)
These compound cannot form bonds with water molecules, thus their solubility is limited by the solvation process The solubility of compounds in water is restricted due to strong intermolecular bonds within the crystal structure
Usual formulation approaches do not work, solubility enhancement through the use of a polar promoiety may prove useful If the molecule has brick dust nature, a polar promoiety may work as this strategy which might disrupt the intermolecular interactions that led to the high crystallinity
Grease ball APIs are the candidates for entrapment into various lipid‐and oil‐based nanoformulations Brick dust fraction that dissolves neither in oil nor in water cannot be administered as self‐emulsifying API delivery system

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