Slow release of acetylsalicylic acid by intravitreal silicone oil

Purpose: To assess in vitro the potential of silicone oil as a delivery sys tem for acetylsalicylic acid (ASA) and to evaluate in vivo the pharmacokine tic distribution of salicylic acid (SA) in the eye. Methods: In an experimental model ASA/silicone oil suspension mixed to a co ncentration 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 performe d on two groups, A and B, of New Zealand white rabbits. Salicylic acid conc entrations in ocular tissues, aqueous, vitreous, and blood plasma were eval uated at 6 hours, 24 hours, and 5 days using high performance liquid chroma tography. Results: Salicylic acid was detected in all tissues. The highest levels wer e obtained in the vitreous: 745.4 mug/mL (A) and 640.0 mug/mL (B) at 6 hour s. 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 le vels were 5.2 mug/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 a nd fluids when compared to intravenous administration of maximum doses.