Ocular and Systemic Pharmacokinetics of Baicalein and Baicalin After Intravitreal Injection and Oral Administration in Mice

Background: Glaucoma requires therapies that extend beyond intraocular pressure (IOP)-lowering strategies, and baicalein (BA) offers dual IOP-lowering and neuroprotective potential. This study evaluated the pharmacokinetics of BA and its major metabolite baicalin (BG) in mouse eyes and serum after intravitreal (IVT) and oral administration to determine whether non-invasive oral dosing can achieve IVT-comparable ocular exposure. Methods: BA was administered via IVT injection (100 μM) or oral gavage (20 and 200 mg/kg) in mice, and concentrations of BA and BG in serum and ocular tissues were quantified using a validated ultra-performance liquid chromatography–mass spectrometry (UHPLC/MS) method. Results: After IVT, ocular BA peaked at 331.56 ± 17.75 ng/g at 5 min and declined to 7.13 ± 0.79 ng/g at 4 h, with minimal systemic exposure. Oral administration achieved comparable or higher peak ocular BA levels (380.43 ± 52.85 ng/g at 15 min for 20 mg/kg; 309.70 ± 24.75 ng/g at 5 min for 200 mg/kg), with markedly higher ocular area under the concentration–time curve (AUC: 2455.48 ± 667.83 h·ng/g for 200 mg/kg and 1224.88 ± 751.13 h·ng/g for 20 mg/kg) versus IVT (247.07 h·ng/g). Serum BA and BG peaked at 5 min after oral dosing, with systemic BG exposure substantially exceeding BA. Conclusions: Non-invasive oral BA dosing achieves ocular concentrations comparable to IVT injection, with significantly greater overall exposure and favorable pharmacokinetic profiles. This study provides the first demonstration in mice that non-invasive oral BA administration can replace invasive IVT delivery, establishing a strong rationale for its clinical development in glaucoma and retinal disease management.