Pharmacokinetics of Orbital Topotecan After Ophthalmic Artery Chemosurgery and Intravenous Infusion in the Swine Model.

Surgery, multiagent systemic chemotherapy, and radiation are used for patients with orbital retinoblastoma but are associated with unacceptable short- and long-term toxicity (including death). We studied orbital and systemic exposure of topotecan in the swine model after ophthalmic artery chemosurgery (OAC) and intravenous (IV) delivery. Landrace pigs (n = 3) underwent 30-minute OAC of topotecan (4 mg), and samples were serially obtained from the femoral artery and from a microdialysis probe inserted into the lateral rectus muscle sheath of the infused eye as a surrogate of the orbital irrigation. Animals were recovered, and, after a wash-out period, plasma and microdialysate samples from the contralateral eye were collected after a 30-minute IV infusion of topotecan (4 mg). Samples were quantified by high-performance liquid chromatography, and population pharmacokinetic analysis was conducted using MonolixSuite. After OAC, median topotecan exposure in the orbit was 5624 ng × h/mL (range 3922-12531) compared to 23 ng × h/mL (range 18-75) after IV infusion. Thus, topotecan exposure in the orbit was 218-fold (range 75-540) higher after OAC than after IV infusion despite comparable systemic exposure (AUCpl) between routes (AUCpl, OAC: 141 ng × h/mL [127-191] versus AUCpl, IV: 139 ng × h/mL [126-186]). OAC was more selective to target the orbit because the median (range) orbital-to-plasma exposure ratio was 44 (28-65) after OAC compared to 0.18 (0.13-0.40) after IV infusion. OAC of topotecan resulted in higher orbital exposure than after IV infusion and was a more selective route for local drug delivery. Patients with orbital retinoblastoma may benefit from a multimodal treatment strategy including OAC therapy.