Pharmacokinetic and toxicity study of intravitreal erythropoietin in rabbits

Aim: To study the pharmacokinetics and toxicity of intravitreal erythropoietin (EPO) for potential clinical use. Methods: For toxicity study, 4 groups (60 rabbits) with intravitreal injection (IVit) of EPO were studied (10U, 100U, or 1 000U) per eye for single injection and 0.6 U/eye (the designed therapeutic level in rabbits) for monthly injections (6x). Eye examination, flash electroretinogram (ERG), and fluorescein angiography (FA) were carried out before and after injection. The rabbits were killed for histological study at different intervals. For the pharmacokinetic study, after IVit of 5 U EPO into left eyes, 44 rabbits were killed at different intervals, and the EPO levels in vitreous, aqueous, retina and serum were analyzed by enzyme-linked immunosorbent assay. Results: At all of the time points examined, the eyes were within normal limits. No significant ERG or FA change was observed. The histology of retina remained unchanged. The pharmacokinetic profile of EPO in ocular compartments was summarized as follows. The half-life times of EPO in vitreous, aqueous and serum were 2.84, 3.24 and 2.12 d, respectively; and C-max were 4615.75, 294.31 and 1.60 U/L, respectively. EPO concentrations in the retina of the injected eye peaked at 1.36 U/g protein at 6 h following injection, with the half-life observed to be 3.42 d. Conclusions: IVit of EPO in a wide range is well tolerated and safe for rabbit eyes. At doses up to 10-fold higher than therapeutic levels, EPO has a pharmacokinetic profile with faster clearance, which is favorable for episodic IVit.