Nonclinical Safety and Pharmacokinetics of Intravitreally Administered Human-Derived Plasmin in Rabbits and Minipigs

Abstract

The use of plasmin for pharmacologic vitreolysis and the creation of a posterior vitreous detachment offers several potential advantages over surgery. The nonclinical pharmacokinetics and safety of human-derived plasmin was evaluated following single or multiple intravitreal injections to rabbits and minipigs. Single intravitreal injections of plasmin at 45-900 microg resulted in a no adverse effect level (NOAEL) of 45 microg in both species; effects at higher doses included chemosis, mucopurulent discharge, mononuclear cell infiltrates in the iris-ciliary body, and reversible changes in electroretinogram waveforms and parameters. No retinal histopathology abnormalities were observed. Following 4 weekly intravitreal injections at 4-423 microg, a NOAEL of 4 microg was identified. Effects at the higher doses included myosis, iritis, iridolenticular synechiae, and changes in electroretinogram waveforms and parameters that were generally not reversible in the present investigation. Vitreal plasmin concentrations were highest at 30 min after dosing and decreased rapidly; measurable concentrations remained, in some animals, at 24 h. Intravitreal plasmin exposure increased in a less-than-dose-proportional manner and tended to be lower in minipigs than in rabbits. The current findings demonstrate acceptable nonclinical safety and pharmacokinetics of intravitreal human plasmin in rabbits and minipigs and support the clinical development of plasmin for ocular diseases.

Lens Subluxation after Plasmin and SF6 Injections in Rabbit Eyes

“…Previous studies have shown a maximal plasmin enzymatic activity between 15 and 60 minutes after injection [21] , [22] , decreasing thereafter and being either undetected after 24 hours [22] or detected at a very low level [21] . Because of the relatively short half-life of plasmin in the vitreous, the use of this enzyme seems to be well tolerated in the eye because it degrades in a short time following injection.…”

Development and Ex-vivo Evaluation of a Novel Device to Facilitate and Standardize Intravitreal Injections in Rabbits

“…The needle-penetration-point chosen for freehand injections in this study was in line with recently published data [17,18]. The needle-penetration-point of the device was fixed at 3.2 mm posterior to the limbus.…”

“…The injection angle of the device was fixed at 40˚ and this angle has proven to reliably miss the lens in the computer model and the printed eye model during the development phase. Commonly reported injection angles for freehand intravitreal injections in rabbits are approximately 45˚ or are described as directed into the mid-vitreous under direct visualization [17][18][19]. Our results show that none (0/11) of the injections made with the device (either with a 13-mm or 19-mm-needle) led to contrastagent-deposition touching the lens (see Figure 2 c for representative image), while this was the case in 67% (6/9) of freehand injections (see Figure 2 b for representative image).…”

“…Injections which deposited the contrast-agent touching the lens are marked with "♦", injections which did not touch the lens are marked with "○" Figure 3: MRI contrast-agent-deposition scores Contrast-agent was detected in 100% (9/9) of freehand-injections, 83% (5/6) of device guided injections using a 19-mm-needle (which leads to an injection depth of 12 mm) and only 67% (6/9) of device-guided injections using a 13-mm-needle (which limits the injection depth of 6 mm). We had anticipated that the 6-mm injection depth of the device, when used with a 13-mm-needle, would be sufficient; A device used to deliver compounds into the vitreous of humans (who have a larger eyeball than the rabbit) limits the injection depth to 6 mm and most commonly 13-mm-needles which are inserted into the eye to an approximate depth of 10 mm are used for intravitreal injections in rabbits [13,18,22]. The most likely explanation for the missed doses is incorrect positioning of the device.…”