Topical ocular drug delivery enhancement

Nevertheless, there are reports on enhancement of ocular drug absorption by bile salts [33], surfactants [200], and chelators [149], Newton et al. [35] demonstrated that Azone, an enhancer widely tested in transdermal drug delivery [201], increased the ocular absorption of cyclosporine, an immunosuppressant, by a factor of 3, thereby prolonging the survival of a corneal allograft. In 1986, Lee et al. [34] reported that 10 pg/mL cytochalasin B, an agent capable of condensing the actin microfilaments, increased the aqueous humor and iris-ciliary body concentrations of topically applied inulin (5 kDa) by about 70% and 700%, respectively, in the albino rabbit. 

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]. 

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. 

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