Vaginal Sildenafil for Primary Dysmenorrhea

This open-label, non-randomized mechanistic study will evaluate whether a single 100 mg vaginal sildenafil citrate suppository reduces uterine hypercontractility during menstruation in adults with moderate-to-severe dysmenorrhea. Ten participants will each receive one open-label dose during a single menstrual treatment visit and will serve as their own control: 6 participants with primary dysmenorrhea and no evidence of pelvic pathology, plus a separately analyzed exploratory subset of 4 participants, 2 with known endometriosis and 2 with known uterine fibroids. Uterine contractility will be measured with cine magnetic resonance imaging (MRI) before dosing and approximately 4 hours after dosing. Additional objectives are to evaluate acute menstrual pain over the 4-hour observation window, to document systemic exposure using sparse plasma sampling at approximately 2 and 4 hours after dosing, and to assess short-term safety and local tolerability.