Slow Release of Acetylsalicylic Acid by Intravitreal Silicone Oil

Purpose: To assess in vitro the potential of silicone oil as a delivery system for acetylsalicylic acid (ASA) and to evaluate in vivo the pharmacokinetic distribution of salicylic acid (SA) in the eye.

Methods: In an experimental model ASA/silicone oil suspension mixed to a concentration of 1.67 mg/mL was investigated for release rate of ASA and SA. In vivo vitrectomy and intravitreal injection of two different ASA/silicone oil suspensions, both mixed to a concentration of 1.67 mg/mL, was performed on two groups, A and B, of New Zealand white rabbits. Salicylic acid concentrations in ocular tissues, aqueous, vitreous, and blood plasma were evaluated at 6 hours, 24 hours, and 5 days using high performance liquid chromatography.

Results: Salicylic acid was detected in all tissues. The highest levels were obtained in the vitreous: 745.4 microg/mL (A) and 640.0 microg/mL (B) at 6 hours. The retina followed with 332.9 ng/mg (A) and 281.3 ng/mg (B) at 6 hours and 31.6 ng/mg (A) and 48.1 ng/mg (B) at day 5. The maximum blood plasma levels were 5.2 microg/mL.

Conclusion: Silicone oil is an efficacious delivery system of ASA in vitro and in vivo. Higher concentrations of SA were found in all ocular tissues and fluids when compared to intravenous administration of maximum doses.