Synergistic antidiabetic efficacy of dorzolamide and metformin: HPTLC quantification and biological evaluation

Dorzolamide (DOR), a carbonic anhydrase inhibitor primarily used for glaucoma, may exert antidiabetic effects by modulating metabolic pathways such as gluconeogenesis and lipogenesis. This study investigated the potential of DOR as a therapeutic agent for diabetes mellitus (DM) and evaluated its synergistic efficacy with metformin (MET) in an alloxan-induced diabetic rabbit model. A sensitive and selective high-performance thin-layer chromatography (HPTLC) method was developed and validated for the simultaneous quantification of DOR and MET in biological matrices. Five groups of male Boskat rabbits (n = 6) were treated with saline, MET (10 mg/kg), DOR (10 mg/kg), or a DOR-MET combination. Notably, while DOR and MET monotherapies reduced blood glucose levels (BGLs) by approximately 32% and 28%, respectively, their co-administration produced a significant synergistic effect, resulting in a 48% reduction in BGLs (p < 0.001). HbA1c levels followed a comparable downward trajectory. Chromatographic separation was achieved on HPTLC silica gel 60 plates with a mobile phase composed of methanol, glacial acetic acid, and 25% ammonia in a volumetric ratio of 5:0.5:0.075, demonstrating excellent linearity (25-1200 ng/band) and low limits of detection (3.14 ng/band for DOR; 3.3 ng/band for MET). Histopathological analysis confirmed the protective effects of the combination, revealing preserved pancreatic islet morphology and reduced hepatic cellular degeneration. This investigation is the first to demonstrate the antidiabetic synergy of DOR and MET, supported by biochemical, histological, and chromatographic evidence. The validated HPTLC‑densitometric method provides a simple, sensitive, and cost‑effective tool for routine analysis, while the biological findings highlight a promising therapeutic strategy for DM management.