Formulation Screening and Characterization of PLGA-Based Injectable In Situ Gel Loaded with Progesterone.

Objective

Conventional progesterone (P4) formulations suffer from low bioavailability, severe local irritation, and poor patient adherence due to P4's poor aqueous solubility. This work aimed to develop and screen a biodegradable PLGA/NMP (Poly(lactic-co-glycolic acid)/N-methyl-2-pyrrolidone) injectable in situ gel for sustained P4 delivery to overcome these clinical limitations. Significance: Commercial oral, vaginal, and oil-based intramuscular P4 preparations cannot maintain stable long-term drug exposure, and they cause injection-site pain/inflammation. The screened in situ depot system reduces administration frequency and local tissue irritation, supporting convenient luteal phase support and pregnancy maintenance.

Methods

Nine formulations with variable P4 loading (10-50% w/w) and PLGA concentration (15-55% w/w) were fabricated. Formulations were screened via three core endpoints: injectability (injection force and discharge rate), in vitro sustained release in 10% Hydroxypropyl-β-cyclodextrin (HP-β-CD)-Phosphate-buffered saline (PBS) sink medium, and 7-day subcutaneous histocompatibility in rats. high-performance liquid chromatography (HPLC) was validated for progesterone quantification; Hematoxylin and eosin (H&E) staining assessed local inflammatory responses.

Results

Formulations with progesterone ≤ 30% w/w and PLGA ≤ 35% w/w exhibited acceptable injectability (injection force < 50 N; discharge rate > 79%). Higher PLGA concentrations suppressed initial burst release (16.74% at 8 h for 35% PLGA vs. 29.8% for 20% PLGA). All formulations formed stable ellipsoidal subcutaneous depots and completed progesterone release within 4 days. Histopathology revealed only mild local inflammation (histological score = 1) without severe necrosis, superior to highly irritating oil injections in formulation control groups.

Conclusions

The screened PLGA-based progesterone in situ gel resolves critical drawbacks of traditional progesterone dosage forms. This low-irritation, sustained-release injectable platform provides a scalable industrial formulation candidate for long-acting hormone therapy.