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Peter A Simmons, Hongpeng Wang, Tao Wang, Richard Meller, Joseph Glennon Vehige; Sodium concentration affects the physical properties of hyaluronic acid-based lubricant eye drops. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4899. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Hyaluronic acid (HA) solutions are commonly prescribed for dry eye. HA polymer size has been shown to have a large range among commercially-available solutions, with low-shear viscosity a function of polymer size and concentration. For HA ophthalmic formulations, overall solution osmolality is generally a function of sodium concentration, except for solutions that contain alternative non-electrolytes (organic osmolytes) replacing sodium. This study examined whether sodium concentration has a direct effect on overall formulation viscosity, which in turn may influence on-eye performance relative to comfort and residence time.
A commercially-available lubricant eye drop formulation containing HA, carboxymethylcellulose, the non-electrolyte organic osmolytes glycerine, l-carnitine, and erythritol, plus a lactate buffer (Optive Fusion UD, Allergan) was modified by replacing the organic osmolytes with NaCl to a concentration of 0.55%. Both solutions had a total osmolality of 286 mOsm/kg, as determined on a standard freezing point depression osmometer (Model 2020, Advanced Instruments). Rheological performance was measured on a research rheometer (Model DHR-3, TA Instruments) at 35 °C using a flow procedure in the shear rate range from 1 to 10,000 (1/s).
Both test formulations exhibited the characteristic shear-thinning of HA lubricant eye drops. Replacement of organic osmolytes with sodium resulted in a significant reduction in measured viscosity at all shear rates, ranging from a 20% drop at 1/sec (0.14 to 0.11 poise) to a 10% drop at 10,000 1/sec (0.053 to 0.047 poise).
Lower sodium concentration may be desirable for dry eye treatments, as excess salt in the tear film is associated with up-regulation of inflammatory processes, ocular surface damage, and symptoms of discomfort. The present results also demonstrate that added sodium in a formulation significantly alters the viscosity profile. HA solutions with low sodium have higher low-shear viscosity for a given concentration, which may improve retention time and duration of benefit for dry eye patients.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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