SOLID LIPID NANOPARTICLES: EMERGING COLLOIDAL CARRIERS AS OCULAR DRUG DELIVERY SYSTEMS

Numerous attempts have been made to improve the bioavailability from ocular drug delivery systems and to prolong the residence time of drugs applied topically onto the eye. Conventional ocular drug delivery systems such as eye drops and ointments are inefficient, whereas, systemic administration requires high doses which may result in significant toxicity. Therefore, a need arises to develop novel drug delivery carrier systems capable of increasing ocular bioavailability and decreasing both local and systemic cytotoxicity. Nanotechnology is expected to revolutionize ocular drug delivery. Solid lipid nanoparticles (SLNs) introduced in 1991 represent an alternative carrier system to traditional colloidal carriers, such as emulsions, liposomes and polymeric micro- and nanoparticles. SLNs do not show biotoxicity as they are prepared from physiological lipids and are ideal ocular drug delivery systems as they can enhance the corneal absorption of drugs and improve the ocular bioavailability of both hydrophilic and lipophilic drugs. SLNs have another advantage of allowing autoclave sterilization, an indispensible step in the formulation of ocular preparations. In this review a special attention has been given to the nature of lipids and surfactants commonly used for SLNs production. This article also reviews in detail the various fabrication methods, characterization, sterilization, and stabilization techniques for SLNs. In-vitro and in-vivo methods to study the drug release profile from SLNs have also been mentioned. A summary of previous studies involving the use of SLNs in ocular drug delivery is provided, along with a critical evaluation of SLNs as a potential colloidal ocular drug delivery system.