ophthalmic

Nanoemulsions are only kinetically stable. However, the long term physical stability of nanoemulsions (with no apparent flocculation or coalescence) makes then unique and they are sometimes referred to as ‘Approaching thermodynamic stability. The inherently high colloid stability of nanoemulsions can be well understood from a consideration of their stearic stabilization (when using non-ionic surfactants and /or polymers) and how this is affected by the ratio of the adsorbed layer thickness to droplet radius. Successful ocular drug delivery has largely eluded solution due to, the physiological constraints imposed by the protective mechanisms of the eye that lead to poor absorption of drugs with very small fractions (less than 5%) of the instilled dose penetrating the cornea and reaching the intraocular tissues. Low drug contact time and poor ocular bioavailability due to drainage of solution, tear turnover and its dilution or lacrimation are the problems associated with conventional systems. Novel systems offer manifold advantages over conventional systems as they increase the efficiency of drug delivery by improving the release profile and also reduce drug toxicity. Conventional delivery systems get diluted with tear, washed away through the lacrimal gland and usually require administering at regular time intervals whereas novel emulsions are stable, have improved solubility, required reduced dosing frequency and release drug for prolonged periods of time. The aim of this review focuses on micro and nanoemulsions between 1 and 200 nm with a mean droplet size of about 40nm) for ocular drug delivery.

Conventional liquid ophthalmic formulations are most convenient from patient point of view. But these formulation shows low bioavailability because of a constant lachrymal drainage in the eye which leads to frequent dosing. Moreover, the absorption of the drug drained through the nasolacrymal duct may result in undesirable side effects. To overcome these limitation different approaches has been applied such as ointment, gel, cream etc. These ophthalmic formulations also fails to show desired therapeutic responses because of their own disadvantages such as ointment makes blurred vision. So two different systems was combined together as niosomes and in-situ gel by incorporating niosomes in in-situ gel formulation so that it is easy to administered and retain at the site for prolong period of time. The Ofloxacin (OFL), a second generation fluoroquinolone derivative used in eye infections needs frequent dosing in its solution form. Vesicular system reported prolonged and controlled action at corneal surface but it has again limitation of drainage along tear produced.  In this, first niosomes containing ofloxacin were prepared by applying 32 full factorial designs and evaluated for its vesicle size, percent entrapment, in-vitro drug release kinetics and their stability. Also in-situ gel formulation was prepared by dispersing the niosomes in solution of carbopol 940 and Hydroxy Propyl Methyl Cellulose (HPMC) K4M. In-vitro drug release kinetics from niosomal in-situ gel formulation indicates that the minimum inhibitory concentration (MIC) of drug (4 μg/ml) was achieved within 1-2 hrs (batch G1-G9).