Emulsion drug bioavailability

Halofantrine. a highly lipophilic anttmalarial agent, was Formulated in lipid vehicles that were either a lipid solution, an emulsion, or a micellar sy.stem. Lymphatic transport was a major contributor to oral bioavailability. The rank order effect of the vrfiicles for ihc promotion of lymphatic transport was micelles > emulsion > lipid solution (62) (Fig 12). These overall results underline the promising properties of emulsion drug carriers as dierapeutic delivery systems for a variety of drugs (Table 5). 

Another type of novel mueoadhesive formulations was suggested to be submieron emulsions (o/w), bearing droplets eoated with Carbopol 940. These formulations have been shown to generate a 12-fold enhaneement in rats in the oral bioavailability of the antidiuretie peptide drug desmopressin [91]. 

In conclusion, the approval of Restasis by the FDA is an important milestone in lipid emulsion research for ophthalmic application. This approval reflects the achievements of the last decade in terms of the availability of better ingredients, improved manufacturing processes, feasibility of sterilization, and better understanding of the optimization process. In all of the comparative studies done so far, positively charged SME achieved better ocular bioavailability regardless of the studied drug. Research efforts are underway to further explore the mechanism of interaction of positively charged SMEs with ocular tissues and to translate the results of this research into enhanced clinical performance. 

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. 

Routine parenteral administration by injection serves to deliver drugs to specific body tissues. The most important routes of injection of these sterile products are intramuscular (im), intravenous (iv) and subcutaneous (sc). Basic parenteral formulation involves the selection of appropriate bases (e.g. aqueous, oily and emulsions) to achieve the desired bioavailability following injection. The detailed description of... 

Emulsions have been used for centuries for the oral administration of medical oils and vitamins and as dermatological vehicles. Recently, their application has been extended as drug carriers in the delivery and targeting of ophthalmic drags. An indomethacin emulsion has been reported to increase ocular bioavailability and efficacy compared to commercially available formulation in rabbits. 0.4% indomethacin emulsion showed 2.2 fold increase in the area under the anterior aqueous drag concentration/time curve compared to a 1% indomethacin suspension. The emulsion formulation also reduced ocular surface irritation caused by indomethacin Similar advantages have been shown for a pilocarpine emulsion which produced a prolonged therapeutic effect in comparison with pilocarpine hydrochloride eyedrops in man. It can be administered only twice a day, rather than four times daily for conventional formulation. 

Several studies have reported on the enhanced bioavailability of cutaneous drugs using o/w and w/o MEs compared to conventional emulsions, gels or solutions, mesophases, micellar and inverse micellar systems, and vesicles [93], Moreover, a diverse range of drug molecules such as ketoprofen, apomorphine, estradiol, lido-caine [94-97], indomethacin and diclofenac [98], prostaglandin Ei [99], aceclofenac... 

When compared to either saline or anionic emulsions, the nanosized cationic emulsions were shown to enhance the ocular bioavailability of indomethacin [108], piroxicam [178], and cyclosporin A [106,179] following one single-drop dose instillation into the rabbit eye (Figure 4). A significant drug reservoir effect was noted in the cornea and conjunctiva even for more than 8 h following the instillation [106],... 

The aqueous solubility of a drug in the 2-8 pH range has a direct influence on its oral and parenteral formulations. A drug with poor solubility (i.e., less than O.lmg/ml) in acidic media may show poor and erratic oral bioavailability due to the dependency of absorption processes in GI fluids. Intravenous dosing requires that the drug be administered in a soluble form. The adjustment of pH, the addition of a cosolvent or a ligand for complexation, or the formation of an emulsion may permit solubilization, but each of these techniques has limitations. Rapid intravenous... 

Lipid-based formulations of poorly water soluble drugs offer large versatility for oral administration as they can be formulated as solutions, gels, suspensions, emulsions, self-emulsifying systems, multiple emulsions, microemulsions, liposomes, and solid dispersions. " Administration of a drug in a lipidic vehicle/formu-lation can enhance the absorption and oral bioavailability via a combination of various mechanisms " " that are briefly summarized as follows ... 

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