The delivery of drugs to the posterior segment of the eye remains a tremendously difficult task. Prolonged treatment in conventional intravitreal therapy requires injections that are administered frequently due to the rapid clearance of the drug molecules. As an alternative, intraocular implants can offer drug release for long-term therapy. However, one of the several challenges in developing intraocular implants is selecting an appropriate in vitro dissolution testing model. In order to determine the efficacy of ocular implants in drug release, multiple in vitro test models were emerging. While these in vitro models may be used to analyse drug release profiles, the findings may not predict in vivo retinal drug exposure as this is influenced by metabolic and physiological factors. This review considers various types of in vitro test methods used to test drug release of ocular implants. Importantly, it discusses the challenges and factors that must be considered in the development and testing of the implants in an in vitro setup.
Bevacizumab is a full-length human monoclonal antibody used to treat various neovascular diseases such as wet age-related macular degeneration (AMD), diabetic eye disease and other problems of the retina. Monthly intravitreal injections of bevacizumab (Avastin®) are effective in the treatment of wet AMD. However, there is a growing demand in the development of sustained release ophthalmic formulations. Therefore, this study aims, for the first time, to develop a rapid, simple, and sensitive method using size exclusion chromatography coupled with fluorescence detection for routine quantification of bevacizumab in ophthalmic formulations and during in vitro release studies. The selected chromatographic conditions included an aqueous mobile phase composed of 35 mM sodium phosphate buffer and 300 mM sodium chloride (pH 6.8), a flow rate of 0.5 mL/min, and the fluorescence detector was operated at excitation and emission wavelengths of 280 and 340 nm, respectively. The peak area-concentration relationship maintained its linearity over concentration range of 0.1-20 μg/mL (R2 = 0.9993), and the quantitation limit was 100 ng/mL. The method was validated for specificity, accuracy, precision, and robustness. The developed method had a run time of 6 min at temperature 25 °C, making it a unique validated method for rapid and cost-effective quantification of bevacizumab.
The objectives of this study were to develop biodegradable poly-lactic-co-glycolic acid (PLGA) based injectable phase inversion in situ forming system for sustained delivery of triamcinolone acetonide (TA) and to conduct physicochemical characterisation including in vitro drug release of the prepared formulations. TA (at 0.5%, 1% and 2.5% w/w loading) was dissolved in N-methyl-2-pyrrolidone (NMP) solvent and then incorporated 30% w/w PLGA (50/50 and 75/25) polymer to prepare homogenous injectable solution. The formulations were evaluated for rheological behaviour using rheometer, syringeability by texture analyser, water uptake and rate of implant formation by optical coherence tomography (OCT) microscope. Phase inversion in situ forming formulations were injected into PBS pH 7.3 to form an implant and release samples were collected and analysed for drug content using a HPLC method. All formulations exhibited good syringeability and rheological properties (viscosity: 0.19-3.06 Pa.s) by showing shear thinning behaviour which enable them to remain as free-flowing solution for ease administration. The results from OCT microscope demonstrated that thickness of the implants were increased with the increase in time and the rate of implant formation indicated the fast phase inversion. The drug release from implants was sustained over a period of 42 days. The research findings demonstrated that PLGA/NMP-based phase inversion in situ forming implants can improve compliance in patient's suffering from ocular diseases by sustaining the drug release for a prolonged period of time and thereby reducing the frequency of ocular injections.