Oral solution drug delivery applications

The size of the microparticles that can be controlled by the concentration of the dope solution, flow rate and applied voltage, are in the range of 100-300 ym. The sweUing and dissolution of the sericin microparticles are suppressed at pH 2.2 and increased at pH 7.4, indicating their potential in oral drug delivery applications. Diclofenac was used as a model drug, and its release from the sericin microparticles was suppressed in a stomach-simulated fluid but was increased in a small intestine-simulated fluid (61). 

Water-soluble polymers can also be used as aqueous solutions for drug delivery. Although the polymer is already dissolved, its increase in viscosity of the drug solution causes the drug to be retained somewhat longer in the desired application. This technique is common with ocular, nasal, and oral applications of drug solutions. 

In this chapter we will provide a brief overview of the early approaches to bioavailability enhancement by use of simple lipid-based delivery systems (lipid solutions, emulsions etc), and then describe recent progress in the application of self-emulsifying- and microemulsion-based formulations. The effects of lipids on the oral bioavailability of co-administered poorly water-soluble drugs may also be classified from a mechanistic (and to a degree, historical) perspective as physicochemically mediated effects (solubility, dissolution, surface area) and biochemically mediated effects (metabolism, transport related events), and these will be approached separately. It is readily apparent, however, that in many cases physicochemically and biochemically mediated mechanisms will operate side by side. In some instances, bioavailability may also be enhanced by the stimulation of intestinal lymphatic transport, and these studies will be addressed in a separate section. 

It has been shown in a number of studies that the incorporation of drug in o/w nanosized emulsions significantly increased the absorption of the drug when compared with the equivalent aqueous solution administered orally [132-135], However, the use of emulsions for oral application is limited since other attractive alternatives, such as self-emulsifying oil delivery systems, which are much less sensitive and easy to manufacture, are available [136,137], Thus the potential of nanosized emulsions after administration with parenteral and traditional nonparenteral topical routes such as ocular, percutaneous, and nasal is covered in this section. 

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