Urology · Clinical trials
Erectile Dysfunction Clinical Trials
Approved therapies, the pivotal-trial endpoints they were judged on, the magnitude of benefit — and the drugs that failed their endpoints, and why.
Indication overview
About erectile dysfunction — and why its trials are hard
Erectile dysfunction (ED) is the persistent inability to attain or maintain a penile erection sufficient for satisfactory sexual performance. It is commonly vasculogenic and frequently signals underlying endothelial or cardiovascular disease, diabetes, or neurologic and hormonal causes. First-line pharmacotherapy is the oral phosphodiesterase type 5 (PDE5) inhibitors, which potentiate nitric-oxide-mediated cyclic GMP signalling to enhance cavernosal smooth-muscle relaxation and inflow. Sildenafil (Viagra, 1998) established the class, followed by tadalafil (Cialis, 2003) with a long duration allowing daily dosing, vardenafil (Levitra, 2003), and avanafil (Stendra, 2012) with rapid onset. For non-responders, options include intracavernosal or intraurethral alprostadil (a prostaglandin E1), vacuum devices, and penile prostheses. Pivotal trials use the International Index of Erectile Function (IIEF), particularly its erectile function domain, together with Sexual Encounter Profile questions SEP2 (penetration) and SEP3 (maintenance to completion). This is a mature, highly effective therapeutic area; PDE5 inhibitors are contraindicated with nitrates due to hypotension. Development history also includes agents abandoned over safety, notably intranasal bremelanotide.
Approved therapies & pivotal evidence
What's been approved — and by how much it moved the endpoint
| Drug (brand) | Approved | Setting | Pivotal trial | Primary endpoint | Magnitude of benefit |
|---|---|---|---|---|---|
| Sildenafil (Viagra) | 1998 | Oral PDE5 inhibitor, first-in-class, on-demand for ED | Pivotal Phase 3 (Goldstein et al., NEJM 1998) | IIEF erectile function domain; SEP questions on successful intercourse | Marked improvement: roughly 70-80% of attempts successful vs ~20-25% placebo across dose-response and fixed-dose trials |
| Tadalafil (Cialis) | 2003 | Long-acting oral PDE5 inhibitor for ED (on-demand and daily) | Phase 3 registration trials | Change in IIEF-EF domain; SEP2 and SEP3 | Significant improvement over placebo in IIEF-EF and proportion of successful intercourse attempts; ~36-hour window of efficacy |
| Vardenafil (Levitra) | 2003 | Oral PDE5 inhibitor for ED | Phase 3 registration trials | IIEF-EF domain; SEP2/SEP3 success rates | Significant improvement in erectile function and successful penetration/maintenance vs placebo |
| Avanafil (Stendra) | 2012 | Rapid-onset oral PDE5 inhibitor for ED | REVIVE and REVIVE-Diabetes (Phase 3) | IIEF-EF domain; SEP2 and SEP3 | Significant improvement vs placebo with onset as early as ~15 minutes; higher successful-attempt rates than placebo |
| Alprostadil (prostaglandin E1) (Caverject (intracavernosal) / MUSE (intraurethral)) | 1995 | Locally administered vasodilator for ED, including PDE5-inhibitor non-responders | Phase 3 registration trials | Erectile response sufficient for intercourse | High rate of clinically adequate erections; limited by administration route and penile pain |
Where trials have failed
Drugs that missed their endpoint — and what contributed
The most instructive lessons in erectile dysfunction development come from programmes that failed the endpoint that mattered.
| Drug / trial | Endpoint outcome | What contributed |
|---|---|---|
| Bremelanotide (PT-141, melanocortin agonist), intranasal formulation — Phase 2 development for erectile dysfunction | Intranasal development for ED was discontinued because of dose-related increases in blood pressure; the compound was later reformulated as subcutaneous therapy and approved for hypoactive sexual desire disorder in women (Vyleesi, 2019), not ED. | Clinically significant transient hypertension with the intranasal route created an unacceptable cardiovascular risk-benefit balance for an ED indication. |
| Apomorphine sublingual (Uprima) — Phase 3 registration program (US) | Did not gain FDA approval for ED in the US; the application was withdrawn/not approved amid concerns about syncope and hypotension, though it was marketed in Europe. | Dose-related nausea, hypotension, and syncope narrowed the therapeutic window and undermined the risk-benefit profile relative to emerging PDE5 inhibitors. (US regulatory specifics partly unverified.) |
Choosing the right endpoint
Primary endpoints that matter in erectile dysfunction trials
- IIEF Erectile Function domain (IIEF-EF) — Primary validated patient-reported endpoint; a ~4-point change is considered clinically meaningful.
- SEP Question 3 (maintenance of erection to completion) — Co-primary responder endpoint capturing successful intercourse.
- SEP Question 2 (ability to achieve penetration) — Co-primary endpoint on erection adequacy for penetration.
- Global Assessment Question (GAQ) — Simple yes/no on whether treatment improved erections; supportive endpoint.
How iNGENū runs erectile dysfunction trials
Physician-led design, built for FDA submission
Endpoint & biomarker strategy
Board-certified specialists design endpoints and patient selection aligned to current FDA guidance for this indication.
FDA-ready data
Built to ICH-GCP and 21 CFR 312.120, with direct FDA submission — data accepted by the FDA, EMA and MHRA.
Faster, lower-cost delivery
~4-week ethics via the TGA CTN scheme, up to 43.5% R&D rebate, and 80–90% below US CRO cost.
Request a fixed-milestone proposal and a tailored endpoint & feasibility summary for this indication.
Frequently asked questions
Erectile Dysfunction clinical trials — FAQs
How do PDE5 inhibitors work and how well?
What distinguishes the four oral agents?
Why are nitrates a concern with these drugs?
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