Water-soluble drugs encapsulation

Adding water miscible solvents to the organic phase enhanced the encapsulation of water-soluble drugs due to rapid polymer precipitation in the aqueous phase [93, 95]. Bodmeier and McGinity [93] investigated using co-solvents... 

Water-soluble drugs cannot be encapsulated with the 0/W-emulsion technique because the drug would be lost to the external aqueous phase. Two methods have been described for the encapsulation of hydrophilic drugs one is based on using an external oil phase and the other one on the formation of the microparticles by a w/o/w-melt dispersion technique. 

A technique based on the formation of a multiple emulsion with an external aqueous phase was developed for the encapsulation of water-soluble drugs in order to replace the external oil phase. Possible unwanted interactions between the oil and the emulsified wax such as swelling or dissolution of the wax, clean-up requirements of the final product, and recovery of the oil phase could be eliminated. In analogy to the encapsulation of water-soluble drugs within polymeric microparticles by a w/o/w-solvent evaporation method, a molten wax phase was used instead of an organic polmer solution. A heated aqueous solution of pseudoephedrine HCl was emulsified into the molten carnauba wax, followed by the emulsification of this w/o-emulsion into a heated external aqueous phase. The temperature of the internal and external aqueous phases had to be kept above the melting temperature of the wax in order to avoid premature... 

Figure 19.2. (a) Small unilamellar liposome (SUV, 20-50 nm). (b) Multilamellar vesicles (MLV, up to 10 um), (c) Large unilamellar vesicle (LUV, 50 nm-10 um). (d) A liposome can encapsulate water-soluble drugs inside the cavity and nonpolar molecules within the... 

Also, liposomes (see later) are very similar but are formed by the self-assembly of phospholipid molecules in an aqueous environment. The amphiphilic phospholipid molecules form a closed spherical bilayer in an attempt to shield their hydrophobic groups from the aqueous environment, whilst still maintaining contact with the aqueous phase via the hydrophilic head group. The resulting closed sphere may encapsulate water-soluble drugs within the inner aqueous compartment or may encapsulate lipid soluble drugs within the bilayer membrane. Alternatively, lipid soluble drugs may be complexed with a hydrophilic cyclodextrin and then encapsulated within the liposome aqueous compartment. 

In these systems, CyDs can improve the drug stability (against light or hydrolysis), and enhance the encapsulation rate of poorly water-soluble drugs. 

Normally the water-soluble drug is added during the hydration process and subsequently the loaded polymersomes are purified by the original solution by either dialysis or size exclusion chromatography [68]. However, this method ensures relative high encapsulation efficiency only if combined with post processing by extrusion or sonication [51,112]. Interaction between copolymers and the desired molecules certainly favours the efficiency. pH sensitive systems such as PMPC-PDPA showed efficient encapsulation efficiency due to the strong interaction between the polymers and the DNA prior to pH variation [51,70,113]. 

Water-in-oil microemulsion, having water microdroplets dispersed in the continuous oil phase, has the ability to encapsulate water-soluble drugs in the water microdroplets and has emerged as a successful dosage form for the delivery of hydrophilic drug. 

Elkharraz K, Ahmed AR, Dashevsky A, Bodmeier R. Encapsulation of water-soluble drugs by an o/o/o-solvent extraction microencapsulation method. International Journal of Pharmaceutics. May 16, 2011 409(l-2) 89-95. PubMed PMID 21356287. 

It is known that the preparation of mierospheres by using 0/W emulsions is not an effieient method for die entrapment of water-soluble drugs as the eompounds rapidly dissolve in the aqueous eontinuous phase and are lost It has been widely aeeepted that the problem of inefficient eneapsulation of water-soluble dmgs ean be overcome by using the double-emulsion solvent-evaporation technique. Water-insoluble drugs are usually satisfactorily encapsulated by the 0/W emulsion teehnique (64, 65). 

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