Sildenafil Citrate
Sildenafil citrate is a selective PDE5 inhibitor used in adult men for erectile dysfunction. It supports erections by raising cyclic GMP levels in penile tissue during sexual stimulation. Available under brand and generic names.
- Chemical formula
- C22H30N6O4S
- CAS number
- 171599-83-0
- ATC code
- G04BE03
- Molecular weight
- 666.7 g/mol
- Drug class
- PDE5 inhibitor
- Also known as
- Sildenafil, UK-92,480
What is it?
Sildenafil citrate is the salt form of sildenafil, a small-molecule drug originally developed in the early 1990s by Pfizer as a candidate for angina pectoris. During clinical trials its primary effect on penile erections was identified, and the compound was approved in 1998 under the brand name Viagra. It is now one of the most widely prescribed treatments in adult andrology, both as a brand and as authorised generics.
Mechanism of action
Sildenafil citrate selectively inhibits phosphodiesterase type 5 (PDE5), an enzyme that breaks down cyclic guanosine monophosphate in the corpus cavernosum. By blocking PDE5, the drug allows cGMP — produced when nitric oxide is released during sexual stimulation — to accumulate. This relaxes the smooth muscle of the penile arteries, increases blood inflow and supports erection. The molecule does not initiate the chemical cascade itself; arousal is required.
Pharmacokinetics
After oral administration sildenafil citrate is absorbed rapidly, with peak plasma concentrations typically reached within 30 to 120 minutes on an empty stomach. The bioavailability is about 40%. The drug undergoes hepatic metabolism mainly via CYP3A4 to an active metabolite, and is eliminated primarily through the faeces. The terminal half-life is approximately three to five hours, which corresponds to a clinical effect of up to four hours.
Indications
Sildenafil citrate is approved in adult men for the treatment of erectile dysfunction. A second formulation under a different brand is approved for pulmonary arterial hypertension at lower per-tablet doses. The compound is not approved for use in women, paediatric populations or as a recreational stimulant. According to the prescribing information, off-label use should be discussed with a qualified healthcare professional.
Safety profile
Common adverse effects reported in clinical trials include headache, facial flushing, nasal congestion, dyspepsia and transient visual disturbances. Serious but rare events include sudden hearing loss and priapism. The combination with organic nitrates is contraindicated due to the risk of severe hypotension. According to the manufacturer's prescribing information, anyone with cardiovascular disease, hepatic impairment or active medication therapy should consult a clinician before use.
Products containing this ingredient
Frequently asked questions
Is sildenafil the same as sildenafil citrate? ▾
In practice, the two terms are used interchangeably. The active molecule is sildenafil; sildenafil citrate is the citrate salt that is actually formulated into oral tablets, because it has better solubility and stability than the free base. Regulatory documents and prescribing information generally list both names. The clinical effects discussed for one apply to the other when administered at equivalent doses.
How is sildenafil different from tadalafil? ▾
Both are PDE5 inhibitors used for erectile dysfunction, but their pharmacokinetic profiles differ. Sildenafil reaches peak concentrations in roughly one hour and has a half-life of three to five hours, supporting an effect of up to four hours. Tadalafil reaches peak more slowly and has a half-life of about 17 hours, giving an effect window of up to 36 hours. Choice between them depends on the prescriber's assessment.
Does sildenafil require sexual stimulation? ▾
Yes. Sildenafil works by amplifying the chemical signal that produces an erection during sexual arousal — it does not start that signal. Without sexual stimulation, the nitric oxide pathway in the corpus cavernosum is not activated, and the medication has no perceptible effect. This requirement is repeated in the manufacturer's prescribing information.
Can sildenafil be used by women? ▾
Sildenafil is not approved for the treatment of female sexual dysfunction. A small number of clinical studies have explored possible effects on female arousal, but the evidence base does not support routine prescription. According to regulators, the medication should not be used by women without medical supervision.
What are the main contraindications for sildenafil? ▾
The most important contraindication is concurrent use of organic nitrates or guanylate cyclase stimulators, where combined therapy can cause a severe drop in blood pressure. Other situations requiring caution include severe hepatic impairment, recent stroke or heart attack, low blood pressure, severe cardiovascular disease and known hypersensitivity to the molecule. According to the prescribing information, a clinician should review medical history before any prescription.
The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.