Topical ocular drug delivery emulsions

TABLE 5 Selected List of o/w Nanosized Emulsions for Ocular Topical Drug Delivery... 

Over the last decade, o/w nanosized emulsions containing either anionic or cationic droplets have been recognized as interesting and promising ocular topical delivery vehicles for lipophilic drugs. Complete details are available elsewhere [117]. As an overview of this topic, important results on emulsion-based ocular topical drug delivery are covered below and are listed in Table 5. 

To enhance encapsulation efficiency, a spray-drying method could be proposed. Thus, this technique provides a significant improvement of betamethasone encapsulation efficacy into PLGA microparticles, namely, 90% encapsulation efficacy compared with 15% for Wi/o/ W2 double emulsion process [28]. An emulsification/spray-drying technique has also been proposed as an alternative to the double emulsion method for encapsulation of peptide drug, vancomycin into microspheres for the topical ocular delivery (encapsulation efficacy 84-99%) [29]. 

The use of ttaditional disperse systems, e.g., macroemulsions, in the pharmaceutical industry has been limited due to manufacturing complexity and stability problems [117]. The characteristic properties of nano-emulsions (kinetic stability, small and controlled droplet size, etc.) make them interesting systems for pharmaceutical applications. Indeed, nano-emulsions are used as drug delivery systems for administration through various systemic routes. There are numerous publications on nano-emulsions as drug delivery systems for parenteral [17,18,28,29,118-124], oral [25,125-129], and topical administration, which includes the administration of formulations to the external surfaces of the body skin [32,130,131] and to the body cavities nasal [30,132] as weU as ocular administration [31,133-136]. Moreover, many patents concerning pharmaceutical applications of nano-emulsions have been registered [17,18,25,137-145]. An application of nano-emulsions in this field has been in the development of vaccines [33,146-147]. 

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. 

Oil-in-water microemulsion has been widely studied and used for transdermal delivery of the drugs. Apart from its advantages as topical formulation, oil-in-water emulsion also offers numerous advantages such as bioavailability enhancement via transdermal, oral, ocular, and vaginal routes. 

There are several oil-based formulations for the delivery of hydrophilic and lipophilic drugs, which maj orly include emulsions and gels (Figure 58.2). Apart from these, various other novel formulations may also be named under this category such as micelles, reverse micelles, solid lipid nanoparticles, and liposomes. - Based on the physicochemical properties of the drug and patient requirements, the vegetable oil-based formulations may be delivered by various routes like oral, parenteral, topical, transdermal, pulmonary, or ocular, etc., - ... 

Another application of nano-emulsions in the pharmaceutical field is in ocular administration (a topical administration). Nano-emulsions are used as ocular delivery systems to sustain the pharmacological effect of drugs in comparison with their respective aqueous solutions [133]. 

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