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Pharmacokinetic analysis of topotecan after intra-vitreal injection. Implications for retinoblastoma treatment.

Abstract
Topotecan is a promising drug with activity against retinoblastoma, however, attaining therapeutic concentrations in the vitreous humor is still a challenge for the treatment of vitreous seeds in retinoblastoma. Our aim was to characterize topotecan pharmacokinetics in vitreous and aqueous humor, and to assess the systemic exposure after intra-vitreal injection in rabbits as an alternative route for maximizing local drug exposure. Anesthetized rabbits were administered intra-vitreal injections of 5 microg of topotecan. Vitreous, aqueous, and blood samples were collected at pre-defined time points. A validated high-performance liquid chromatography assay was used to quantitate topotecan (lactone and carboxylate) concentrations. Topotecan pharmacokinetic parameters were determined in vitreous, aqueous and plasma using a compartmental analysis. Topotecan lactone concentrations in the vitreous of the injected eye were about 8 ng/mL 48 h after drug administration. The median maximum vitreous, aqueous and plasma total topotecan concentrations (C(max)) were 5.3, 0.68 and 0.21 microg/mL, respectively. The C(max) vitreous/aqueous of treated eyes and the C(max) vitreous/plasma were approximately 8 and 254, respectively. Total topotecan exposure (AUC) in the vitreous of the injected eye was 50 times greater than the total systemic exposure. These findings suggest that intra-vitreal administration of only 5 microg of topotecan reaches significant local levels over an extended period of time while minimizing systemic exposure in the rabbit. Intra-vitreal topotecan administration offers a promising alternative route for enhanced drug exposure in the vitreous humor with potential application for treatment of vitreal seeds in retinoblastoma while avoiding systemic toxicities.
AuthorsEmiliano Buitrago, Christian Höcht, Guillermo Chantada, Adriana Fandiño, Elliot Navo, David H Abramson, Paula Schaiquevich, Guillermo F Bramuglia
JournalExperimental eye research (Exp Eye Res) Vol. 91 Issue 1 Pg. 9-14 (Jul 2010) ISSN: 1096-0007 [Electronic] England
PMID20307538 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
CopyrightCopyright 2010 Elsevier Ltd. All rights reserved.
Chemical References
  • Antineoplastic Agents
  • Topotecan
Topics
  • Animals
  • Antineoplastic Agents (pharmacokinetics, therapeutic use)
  • Aqueous Humor (metabolism)
  • Biological Availability
  • Chromatography, High Pressure Liquid
  • Injections
  • Rabbits
  • Retinal Neoplasms (drug therapy)
  • Retinoblastoma (drug therapy)
  • Topotecan (pharmacokinetics, therapeutic use)
  • Vitreous Body (metabolism)

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