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Viagra (Sildenafil Citrate)
Sildenafil inhibits phosphodiesterase type 5 to increase cGMP levels, enabling smooth muscle relaxation and penile blood inflow.
Sildenafil is a PDE5 inhibitor indicated for erectile dysfunction treatment that works by enhancing nitric oxide effects to increase penile blood flow. The drug has moderate bioavailability (41%) with rapid absorption and approximately 4-hour half-life, primarily metabolized hepatically via CYP3A4. Major risks include severe hypotension when combined with nitrates or alpha-blockers, and increased exposure with CYP3A4 inhibitors requiring dose adjustments. Clinical use requires careful patient selection and monitoring for drug interactions, particularly with cardiovascular agents.
At a glance
| Generic name | Sildenafil Citrate |
|---|---|
| Sponsor | Pfizer Inc. |
| Drug class | Phosphodiesterase-5 (PDE5) inhibitor |
| Target | Phosphodiesterase type 5 (PDE5) |
| Modality | Small molecule |
| Phase | FDA-approved |
Mechanism of action
Sildenafil enhances the effect of nitric oxide (NO) by inhibiting phosphodiesterase type 5 (PDE5), which is responsible for degradation of cyclic guanosine monophosphate (cGMP) in the corpus cavernosum. During sexual stimulation, NO is released in the corpus cavernosum and activates guanylate cyclase, increasing cGMP levels. By inhibiting PDE5, sildenafil causes increased cGMP accumulation, resulting in smooth muscle relaxation and inflow of blood to the corpus cavernosum. Sildenafil has no direct relaxant effect on isolated human corpus cavernosum and has no effect in the absence of sexual stimulation at recommended doses. In vitro studies demonstrate that sildenafil is highly selective for PDE5, with approximately 4,000-fold selectivity compared to PDE3 (involved in cardiac contractility). However, sildenafil is only about 10-fold more potent for PDE5 compared to PDE6, an enzyme found in the retina involved in the phototransduction pathway, which is thought to be the basis for color vision abnormalities.
Approved indications
- Impotence
- Pulmonary arterial hypertension
Common side effects
- Headache
- Headache
- Flushing
- Flushing
- Dyspepsia
- Dyspepsia
- Nasal Congestion
- Nasal congestion
- Abnormal Vision
- Abnormal vision
- Back pain
- Back pain
Drug interactions
- Nitrates (organic nitrates or organic nitrites)
- Alpha-blockers
- Amlodipine
- Ritonavir (strong CYP3A4 inhibitor)
- Erythromycin or strong CYP3A4 inhibitors (ketoconazole, itraconazole, saquinavir)
Key clinical trials
- Radial Shockwave Therapy for Erectile Dysfunction (NA)
- Asciminib With or Without Sildenafil for Brain Tumors (EARLY_PHASE1)
- Safety of Sildenafil in Premature Infants (PHASE2)
- Sildinafil in Pulmonary Hypertension-Rheumatic Chronic Valvular Disease(RCT) (PHASE2, PHASE3)
- Oral Sildenafil for Exercise Capacity, Dyspnea and Cardiopulmonary Function in COPD (PHASE2)
- Interest of Early Erectile Rehabilitation With Sildenafil After Radiotherapy and Proctectomy for Rectal Cancer (PHASE3)
- Sildenafil Plus Hypothermia to Treat Neonatal Encephalopathy (PHASE2)
- Mono vs. Dual Therapy for Pediatric Pulmonary Arterial Hypertension (PHASE3)
Patents
| Patent | Expiry | Type |
|---|---|---|
Primary sources
Every claim on this page is sourced from regulatory or scientific primary sources. See our editorial policy for full methodology.
| Source | Used for |
|---|---|
| ClinicalTrials.gov | Trial enrolment, design, endpoints, results |
| FDA Orange Book | Patents + exclusivity |
Competitive intelligence
For the full competitive landscape — auto-detected comparators, recent regulatory actions across the set, upcoming PDUFA, patent timeline, sponsor landscape:
- Viagra CI brief — competitive landscape report
- Viagra updates RSS · CI watch RSS
- Pfizer Inc. portfolio CI