Subconjunctival injection of tacrolimus, an immunosuppressive drug better known as an oral transplant medication, has shown a promising safety profile in a controlled rabbit study published in BMC Ophthalmology.
The experimental design was deliberately conservative. Ten white New Zealand rabbits received injections in both eyes, allowing each animal to serve as its own control. In one eye, the researchers injected a freshly compounded 0.03 percent tacrolimus solution; in the other, they injected only water for injection, the same sterile diluent used to prepare the drug. The tacrolimus was compounded by adding water for injection to the contents of a 1,000 microgram Prograf capsule manufactured by Astellas Pharma, a formulation that also carried the capsule’s inactive ingredients: hypromellose, croscarmellose sodium, lactose monohydrate and magnesium stearate.
Because subconjunctival delivery places a drug in direct contact with the conjunctiva, episclera and sclera, the team tracked a focused set of clinically meaningful endpoints. At examinations on days 1, 3, 10 and 30 after injection, they scored tearing, conjunctival hyperemia, chemosis, and scleral necrosis or discoloration. Thirty days after the injections, the rabbits were sacrificed and their enucleated eyes underwent histopathological examination, giving the study both a live clinical window and a microscopic one.
The clinical results were striking for their asymmetry. Neither the tacrolimus eyes nor the control eyes showed tearing or any sign of scleral necrosis or discoloration, the most feared structural complications of an injection near the sclera. But the inflammatory picture diverged sharply between the two groups. The water-injected control eyes developed severe conjunctival hyperemia initially, which improved gradually over the follow-up period, while the tacrolimus-injected eyes showed only minimal hyperemia and chemosis by comparison.
The microscopic findings reinforced the clinical ones. Histopathological examination of the enucleated eyes revealed less lymphocytic infiltration in the tacrolimus group and better-preserved scleral and corneal structures compared with the vehicle-injected controls.
The authors concluded that subconjunctival tacrolimus demonstrated a promising safety profile, with no serious adverse events noted clinically or pathologically.
Several caveats deserve emphasis. This was a small study in ten rabbits with a thirty-day horizon, and rabbits’ ocular anatomy and inflammatory responses do not map perfectly onto human eyes.
It is also worth noting what the study did not attempt. The researchers evaluated safety, not efficacy against any specific disease, so no claims about therapeutic benefit in uveitis, graft rejection or other inflammatory conditions can be drawn from these data.
Subject of Research: Ocular safety of subconjunctival tacrolimus injection in a rabbit model
Article Title: Ocular safety of subconjunctival injection of tacrolimus in rabbits
Article References: Hassanin, Z., Shama, A., Zakaria, N., Mohalhal, I. A., Awad, M., Zaki, I., Elmetwally, A. A., & Shoughy, S. (2026). Ocular safety of subconjunctival injection of tacrolimus in rabbits. BMC Ophthalmology. https://doi.org/10.1186/s12886-026-05487-0
Image Credits: AI Generated
DOI: 10.1186/s12886-026-05487-0
Keywords: tacrolimus, subconjunctival injection, rabbit model, ocular safety, conjunctival hyperemia, chemosis, scleral necrosis, histopathology, immunosuppression, BMC Ophthalmology, ophthalmology, drug delivery
News Source: Louis Brooks. (November 4, 2026). Tacrolimus eye injections pass rabbit safety test. Scienmag.
