Vaginal Sildenafil for Primary Dysmenorrhea

Dysmenorrhea is believed to be driven in part by excessive uterine contractility. Sildenafil, a phosphodiesterase-5 inhibitor, may reduce myometrial hypercontractility through enhanced nitric oxide-cGMP signaling. Prior vaginal sildenafil data suggested acute pain relief, but mechanism and systemic exposure were not well characterized.

This study is a mechanistic biomarker investigation in which uterine contractility measured by cine MRI serves as a functional pharmacodynamic marker of PDE5 inhibition. Participants complete a screening visit (medical history, vital signs, 12-lead ECG, screening laboratory tests, MRI safety screening, questionnaires) and a gynecologic examination visit before dosing. When a participant is menstruating and reporting cramping pain of at least 5 on a 0 to 10 scale, she attends a single treatment visit of approximately 6 hours. At that visit she undergoes a pre-dose cine MRI, self-administers a single 100 mg vaginal sildenafil citrate suppository, and undergoes a repeat MRI at approximately 4 hours after dosing. No MRI is obtained at the 2-hour timepoint. Pain ratings on a 100-mm visual analog scale, vital signs, adverse event assessment, and venous blood samples for plasma sildenafil and its N-desmethyl metabolite are obtained at approximately 2 and 4 hours after dosing. In a prespecified exploratory subset of 2 participants, an additional plasma sample is obtained at approximately 24 hours after dosing at a brief return blood-draw visit. Menstrual effluent is collected during the visit. Electronic side-effect questionnaires are sent at 6 and 24 hours after dosing, and a second gynecologic examination visit occurs within approximately one month after the treatment visit.

There is no placebo and no comparator group. The primary analysis is the within-participant change from pre-dose baseline in the number of uterine contractions during a standardized 10-minute cine MRI acquisition. The planned population of 10 participants comprises 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).

Plasma sampling in this study is deliberately sparse because participants are in acute menstrual pain. Formal pharmacokinetic parameters such as Cmax, Tmax, area under the concentration-time curve, and terminal half-life will not be derived from this study; the samples are intended to document whether measurable systemic exposure occurs after vaginal administration and to relate exposure to hemodynamic and adverse event outcomes.

Inclusion criteria

• Female sex assigned at birth
• Age 18 to 35 years
• History of moderate-to-severe dysmenorrhea
• Regular menstrual cycles of approximately 21 to 35 days
• Willing and able to complete a single menstrual treatment visit
• Able to comply with study procedures, including MRI procedures and vaginal self-administration of study product
• Able to provide informed consent

Exclusion criteria

• Gross pelvic pathology identified by clinical history or by the prespecified review of the baseline research MRI. This criterion does not apply to participants enrolled in the prespecified exploratory cohort with known endometriosis or known uterine fibroids, who are analyzed separately.
• Known hypersensitivity to sildenafil or any formulation component
• Use of nitrates or nitric oxide donors
• Use of any CYP3A4 inhibitor or inducer, including dietary sources such as grapefruit
• Use of another phosphodiesterase type 5 inhibitor
• Use of any alpha-adrenergic blocker or any antihypertensive medication
• Uncontrolled hypertension, defined as systolic blood pressure at or above 140 mmHg or diastolic blood pressure at or above 90 mmHg
• Near-hypotension, defined as systolic blood pressure at or below 95 mmHg or diastolic blood pressure at or below 65 mmHg
• Cardiovascular disease
• Clinically significant electrocardiographic abnormality, as judged by the investigator
• Clinically significant laboratory abnormality, as judged by the investigator
• Hepatic impairment of any severity, assessed by screening hepatic laboratory testing and clinical history
• Severe renal impairment
• Platelet count below 100,000 per microliter or hemoglobin below 10 g/dL on screening complete blood count
• Bleeding disorder
• Peptic ulcer disease
• History of non-arteritic anterior ischemic optic neuropathy, risk factors for non-arteritic anterior ischemic optic neuropathy, or other retinal disorders
• Sickle cell disease
• Active pelvic infection
• Presence of an intrauterine device, because of MRI artifact affecting interpretability
• Other contraindication to MRI or factors that would impair MRI safety or interpretability, including certain metallic implants, metallic injury, or claustrophobia
• Pregnant or breastfeeding
• Any condition that, in the opinion of the investigator, would increase risk or interfere with study participation