Sildenafil Online UK

Sildenafil is a phosphodiesterase type 5 (PDE5) inhibitor originally developed and licensed for erectile dysfunction (ED) under the brand name Viagra.

It works by inhibiting PDE5 in the corpus cavernosum, preventing the breakdown of cyclic guanosine monophosphate (cGMP) and thereby enhancing the vasodilatory effect of nitric oxide released during sexual stimulation.

This results in increased blood flow to the penis and facilitates erection.

Sildenafil was the first PDE5 inhibitor to market and remains one of the most extensively studied ED treatments, with efficacy demonstrated across a wide range of ED aetiologies including psychogenic, organic (vascular, neurogenic, hormonal), and mixed causes.

In clinical trials, sildenafil improved erectile function in approximately 70-80% of men. It has a rapid onset of action (30-60 minutes) and a duration of effect of approximately 4-6 hours.

Since patent expiry, generic sildenafil has become the most cost-effective PDE5 inhibitor. NICE recognises PDE5 inhibitors as first-line pharmacotherapy for ED.

Sildenafil requires sexual arousal to work and does not independently increase libido.

Take one tablet approximately 1 hour before planned sexual activity.

Sildenafil may be taken on an empty stomach or with food; however, a high-fat meal can delay absorption by approximately 1 hour and reduce peak plasma concentration by about 29%.

Do not take more than one dose in 24 hours. Swallow the tablet whole with water.

Avoid excessive alcohol consumption as this independently impairs erectile function and may increase the risk of hypotension.

Grapefruit juice can increase sildenafil plasma levels via CYP3A4 inhibition and should be used cautiously. The drug does not produce an erection without sexual arousal.

The recommended starting dose is 50 mg, taken approximately 1 hour before sexual activity. Based on efficacy and tolerability, the dose may be increased to a maximum of 100 mg or decreased to 25 mg.

In patients aged over 65, those with hepatic impairment, severe renal impairment (creatinine clearance <30 mL/min), or those taking CYP3A4 inhibitors (e.g.

erythromycin, cimetidine), a starting dose of 25 mg is recommended. Co-administration with ritonavir limits the maximum recommended dose to 25 mg in 48 hours.

The maximum recommended dosing frequency is once per day.

Side effects per SmPC frequency categories from clinical trial data.

Very common (≥1/10): Headache (reported in 12-16% of patients), flushing (10-12%).

Common (≥1/100 to <1/10): Dyspepsia, nasal congestion, dizziness, visual disturbances (colour tinge to vision, increased light sensitivity, blurred vision — attributed to mild PDE6 inhibition in the retina), nausea.

Uncommon (≥1/1,000 to <1/100): Vomiting, rash, eye pain, photophobia, tachycardia, palpitations, hypotension, myalgia, epistaxis, drowsiness.

Rare (≥1/10,000 to <1/1,000): Priapism, non-arteritic anterior ischaemic optic neuropathy (NAION), sudden sensorineural hearing loss, seizures.

Visual symptoms are usually mild and transient. If priapism (erection lasting >4 hours) occurs, seek emergency medical treatment to prevent permanent tissue damage.

The MHRA advises reporting any sudden visual or hearing loss during PDE5 inhibitor therapy.

Sildenafil is strictly contraindicated with nitrates and nitric oxide donors due to the risk of severe hypotension.

A minimum 24-hour washout is recommended after taking sildenafil before administering nitrates (compared to 48 hours for tadalafil).

Caution is required in patients with cardiovascular conditions where sexual activity poses a risk: unstable angina, recent MI (<6 months), recent stroke, severe heart failure, or uncontrolled hypertension or hypotension.

Concurrent use with alpha-blockers (e.g.

doxazosin, tamsulosin) may cause symptomatic hypotension; patients should be haemodynamically stable on alpha-blocker therapy before starting sildenafil at the lowest dose.

Not studied in hereditary degenerative retinal disorders such as retinitis pigmentosa.

Anatomical penile deformation (Peyronie's disease, significant curvature) or conditions predisposing to priapism (sickle cell disease, multiple myeloma, leukaemia) warrant caution.

Sildenafil is contraindicated in patients with hypersensitivity to sildenafil or any excipient, concurrent use of organic nitrates or nitric oxide donors in any form, severe hepatic impairment, recent stroke or myocardial infarction, severe hypotension (<90/50 mmHg), and conditions where vasodilatation or sexual activity are inadvisable.

Co-administration with ritonavir at doses exceeding 25 mg sildenafil in 48 hours is contraindicated. Use with guanylate cyclase stimulators (e.g. riociguat) is contraindicated.