Nanoemulsion: Safe, Stable and Effective Formulation System for Ophthalmology

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.