In vitro and In vivo Evaluation of Freeze-Dried Vaginal Bigel of Dolutegravir and Lamivudine for HIV Pre-Exposure Prophylaxis.

HIV remains a major global health concern, disproportionately affecting women. Use of conventional vaginal gels for prophylactic use is limited due to rapid clearance, poor retention and leakage. This study aims to develop and evaluate a novel mucoadhesive vaginal bigel delivering a fixed-dose combination of dolutegravir and lamivudine for enhanced prophylactic efficacy and user compliance. Bigels were formulated using hydrogel composed of gelatin-HPMC-hyaluronic acid and organogel of glyceryl monostearate in olive oil. Lamivudine was incorporated into the hydrogel phase, and dolutegravir was loaded into the organogel. Four formulations were prepared and were assessed for rheological properties and drug content. The best formulations were freeze-dried and evaluated for mucoadhesion, drug release in simulated vaginal and seminal fluids, cytotoxicity, apoptosis, and in vivo pharmacokinetics in rabbits. The best formulations demonstrated pseudoplastic viscoelastic behavior, high drug content (>80%), and sustained mucoadhesive retention for 24 h. Drug release exhibited biphasic kinetics, with rapid lamivudine release followed by sustained dolutegravir release. In vitro cell line studies showed enhanced apoptosis in HeLa cells with minimal toxicity in normal epithelial cells. In vivo pharmacokinetics confirmed prolonged vaginal drug levels above IC₅₀ thresholds, absence of mucosal irritation and subtherapeutic systemic exposure. Therefore, mucoadhesive freeze-dried bigels can provide a safe, effective, and patient-friendly platform for vaginal HIV pre-exposure prophylaxis, addressing key limitations of conventional gels and supporting user compliance.