Periocular distribution and penetration route of topically instilled nipradilol in rabbits. Qualitative and quantitative study.

Abstract

Abstract: : Purpose: We investigated the ocular and periocular distribution of topical nipradilol, and the penetration route of nipradilol to the posterior periocular tissues in rabbits. Methods: Male albino rabbits were used. In the ocular and periocular distribution study, [¹⁴C]nipradilol (1%, 100 µL) was instilled topically on one eye. In the penetration route study, [¹⁴C]nipradilol was injected into anterior chamber (0.1%, 100 µL) and Tenon’s capsule (0.1%, 10 µL) on one eye. Distribution patterns of radioactivity at 15 and 60 minutes after applications were evaluated by whole–head autoradiography. Additionally, [¹⁴C]nipradilol concentration in enucleated posterior retina–choroid at 60 minutes after anterior chamber or Tenon’s capsule injections were measured by liquid scintillation analyzer. Results: In the topical application study, equivalent nipradilol concentration in the periocular tissue around the optic nerve insertion was higher on the ipsilateral side than the contralateral side (p < 0.01). Radioactivity was higher in the periocular tissue behind the equator than around the optic nerve insertion on the ipsilateral side (p < 0.01), but not on the contralateral side. The equivalent nipradilol concentration in the ipsilateral posterior retina–choroid was 2538.6 ± 1141.1 ng/g, which was significantly higher than that on the contralateral control side (108.1 ± 23.0 ng/g, p < 0.01). In anterior chamber injection study, radioactivity was observed in the anterior part of eye including equatorial retina–choroid (69.3 ± 10.5 ng/g) but not in the posterior retina–choroid and the posterior periocular tissues around the insertion in the optic nerve. On the contrary, radioactivity was observed clearly in the posterior retina–choroid and the posterior periocular tissues around the insertion in the optic nerve by Tenon’s capsule injection (131.3 ± 43.8 ng/g). The results of enucleation method confirmed these results. Conclusions: Results of these qualitative and quantitative studies indicated that nipradilol reached to the posterior periocular tissue and retina–choroid by topical application, and penetrates locally into those tissues via the periocular route on the ipsilateral side.

Keywords: comparative anatomy • drug toxicity/drug effects • pharmacology