Tail-vein IV injection is technically difficult because the vessels are small and hard to visualize, often requires heat-lamp vasodilation and firm restraint, and is a common source of failed dosing attempts.

Use retro-orbital venous sinus injection as an easier, less stressful IV route: 1) Apply a topical ophthalmic anesthetic to the eye before injecting. 2) Gently protrude the eye with downward pressure to expose the venous sinus. 3) Insert the needle bevel-down at the medial canthus at roughly a 45-degree angle into the venous sinus. 4) Adult mice reliably tolerate injection volumes up to 150 microliters; neonates tolerate up to 10 microliters, making the technique usable across ages from neonatal to adult.