SODIUM HYALURONATE 0.25-PERCENT USED AS A VEHICLE INCREASES THE BIOAVAILABILITY OF TOPICALLY ADMINISTERED GENTAMICIN

Sodium hyaluronate (SH) solutions have a longer precorneal residence time than isotonic saline solution in rabbits and in humans. The present study investigates the effect of a 0.25% SH vehicle, compared with a phosphate buffer solution (PBS), on the tear concentration after topical administration of gentamicin sulfate (GS) in humans. Eight volunteers received 25 mul 0.5% GS in PBS in the left eye and 25 mul 0.5% GS in 0.25% SH in the right eye. Tear samples of 1 mul were taken from the inferior sulcus using a capillary before instillation and 5, 10, 20, and 40 min after instillation. The tear concentration of GS was determined by radioimmunoassay. There was a statistically significantly higher concentration of GS in the inferior conjunctival sulcus of the SH-instilled eye at 5 min (P<0.01) and at 10 min (P<0.05) after instillation (paired t-test, n=9). At 20 min the concentration of GS in the SH-instilled eye was only slightly higher, and at 40 min GS concentrations in left and right eyes were comparable. SH 0.25% used as a vehicle therefore increases the availability of GS at the ocular surface for at least 10 min. This effect could be due to the prolonged precorneal residence time of SH.