OBJECTIVE: TX-004HR is a low-dose estradiol (E2) softgel vaginal insert designed to be rapidly dissolving and mucoadhesive. This report describes the physical attributes and pharmacokinetic parameters of the softgel vaginal insert evaluated for the treatment of moderate to severe dyspareunia due to menopausal vulvar and vaginal atrophy. METHODS: In vitro dissolution studies with 25-µg E2 inserts were performed and media samples were analyzed for E2 by high-performance liquid chromatography. Effects of body position on E2 bioavailability were assessed in a phase 1, randomized trial of the 25-µg softgel capsule versus a reference product in which women remained supine after dosing (n = 16), and in a substudy (n = 16) in which women were ambulatory or seated after dosing. Estradiol C max, AUC0-24, and t max were measured by high-performance liquid chromatography-tandem mass spectroscopy. A phase 2, randomized study (n = 50) of 10-µg E2 versus placebo inserts assessed timing of capsule disintegration at days 1 and 15. RESULTS: In vitro testing detected more than 80% of E2 in the dissolution medium by 15 minutes (first time point measured). In the phase 1 studies, baseline-corrected E2 plasma levels were not significantly different regardless of supine versus ambulatory/seated position after dosing: C max, 24.1 versus 34.3 pg/mL; AUC0-24, 77.6 versus 93.7 h ·â€Špg/mL; and t max, 2.1 versus 1.9 hours, respectively. In the phase 2 study, no remnants of the softgel capsule were found at day 1 (6 hours) after dosing and day 15. Vaginal discharge was minimal (1/48 women; 2.1%). CONCLUSIONS: The presented data support rapid dissolution of the softgel capsule and similar E2 pharmacokinetic parameters regardless of body position after dosing.