Introduction: An ideal ophthalmic formulation is one that not only prolongs the contact time of the vehicle on the ocular surface but also slows down the drug elimination. The poor bioavailability and therapeutic response exhibited by the conventional ophthalmic solutions due to pre-corneal elimination of the drug may be overcome by the use of in situ gel forming systems. In situ gelling systems increase the viscosity by changing the pH or temperature in the pre-corneal region and lead to an increase of drug bioavailability by slowing drainage. Poloxamers are polyols with thermal gelling properties which are frequently included in ophthalmic formulations to improve the ocular bioavailability of drugs by increasing vehicle viscosity. Areas covered: An overview on the unique physiological characteristics of ocular globe and the limitations and disadvantages of the conventional ophthalmic pharmaceutical formulations. Readers will appreciate the different strategies to improve the absorption of drugs in the ocular globe, especially the incorporation of poloxamers in ophthalmic formulations, understanding the main advantages of the poloxamers and also learning about the different examples of applications of these polymers in ophthalmic pharmaceutical formulations. Expert opinion: Poloxamers offers a new strategy to improve bioavailability and decrease the side effects induced by the systemic absorption of topically applied ophthalmic drugs.

Topical drug treatment aims at providing high concentrations of drugs at the site of application so as to avoid adverse systemic effects associated with oral administration. Smart polymers, or stimuli-responsive polymers, are able to respond to a stimulus by showing physical or chemical changes in their behaviour as, for example, the delivery of the drug carried by them. The thermo-responsive nature of Pluronic® F-127 (Basf, Ludwigshafen, Germany) makes it an excellent candidate for the delivery of drugs at various application sites. In recent years, PF-127, and later, Pluronic lecithin organogels (PLO), have attracted particular interest in the design of dermal and transdermal delivery systems with a view to promoting, improving or retarding drug permeation through the skin, bearing in mind that for topical delivery systems, accumulation in the skin with minimal permeation is desired, while for systemic delivery, the opposite behaviour is preferred. In this review, we discuss the properties and characteristics of PF-127 and Pluronic lecithin organogels (PLO), and present many examples and advantages of the application of these polymeric systems in topical and transdermal administration of drugs. This article is open to POST-PUBLICATION REVIEW. Registered readers (see “For Readers”) may comment by clicking on ABSTRACT on the issue’s contents page.

The unique properties and characteristics of ocular tissues and the whole set of defence mechanisms of the ocular globe make the instillation of ocular drugs into a difficult task with a low rate of therapeutic response. One of the challenges for the new generation of ophthalmic pharmaceutical formulations is to increase the bioavailability of drugs administered by the ocular route and, therefore, their therapeutic efficacy. This can be achieved with the use of some strategies that provide an increase in the formulation pre-corneal residence time, mucoadhesion and penetration across the eye tissues. Colloidal carrier systems have been very successfully used for the selective and targeted delivery of drugs for several routes of administration. In this context, nanoparticles prepared with specific polymers or lipids and coated, dispersed or suspended in polymer solutions with mucoadhesion properties or in situ gelling properties will be an excellent strategy that deserves attention and further research. In this review, the characteristics and main properties of polymeric and lipid nanoparticles are discussed and examples and advantages of the application of these colloidal carrier systems for the ophthalmic administration of drugs are presented. The future directions of the research required in this specific field are also presented.This article is open to POST-PUBLICATION REVIEW. Registered readers (see “For Readers”) may comment by clicking on ABSTRACT on the issue’s contents page.

Context: Nanostructured lipid carrier (NLC) dispersions present low viscosity and poor mucoadhesive properties, which reduce the pre-corneal residence time and consequently, the bioavailability of ocular drugs. Objective: The aim of this study was to prepare thermoresponsive eyedrops based on the combination of lipid nanoparticles and a thermoresponsive polymer with mucomimetic properties (Pluronic® F-127). Materials and methods: NLC_i dispersions were prepared based on the melt-emulsification and ultrasonication technique. Physicochemical and morphological characteristics of the colloidal dispersions were evaluated. The formulation was also investigated for potential cytotoxicity in Y-79 human retinoblastoma cells and the in vitro drug release profile of the ibuprofen was determined. Results: NLC_i showed a Z-average below 200 nm, a highly positive zeta potential and an efficiency of encapsulation (EE) of ∼90%. The gelification of the NLC_i dispersion with 15% (w/w) Pluronic® F-127 did not cause significant changes to the physicochemical properties. The potential NLC-induced cytotoxicity was evaluated by the Alamar Blue reduction assay in Y-79 cells, and no relevant cytotoxicity was observed after exposure to 0–100 µg/mL NLC for up to 72 hours. The optimized formulations showed a sustained release of ibuprofen over several hours. Discussion and conclusion: The strategy proposed in this work can be successfully used to increase the bioavailability and the therapeutic efficacy of conventional eyedrops.