Sildenafil BNF Information: Quick Reference Guide

Looking for essential sildenafil information from the British National Formulary? Our comprehensive guide covers key BNF details including dosages, contraindications, and safety information for sildenafil treatment. Whether you're considering generic sildenafil or branded Viagra, understanding BNF guidelines helps ensure safe and effective treatment for erectile dysfunction under proper medical supervision.

  • Standard BNF dosages: 25mg, 50mg, and 100mg tablets available
  • Contraindications include nitrate medications and severe cardiovascular conditions
  • Maximum one dose per 24-hour period as per BNF guidelines
  • Drug interactions require careful monitoring, especially with blood pressure medications
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Sildenafil
~60 min
~4 hrs
you like to plan ahead
Tadalafil (as-needed)Most prescribed
~30 min
up to 36 hrs
you want a whole weekend covered
Tadalafil Daily
always active
continuous
you never want to think about timing
Vardenafil
~15–30 min
~8 hrs
you want the fastest onset

How ED treatment works in your body.

Increases blood flow

Increases blood flow

When PDE5 is suppressed, blood is able to flow more freely through the body—including to the (you guessed it) penis.

Increase erections

Increase erections

More blood flow to the penis means harder, more satisfying erections once you're sexually stimulated.

Essential BNF Information for Sildenafil Treatment

BNF Dosage Guidelines for Sildenafil

According to the British National Formulary, sildenafil is available in three strengths: 25mg, 50mg, and 100mg tablets. The typical starting dose is 50mg, taken approximately one hour before sexual activity. Based on individual response and tolerability, the dose may be adjusted to 25mg (if side effects occur) or increased to 100mg (if 50mg proves insufficient). The BNF emphasises that only one dose should be taken within any 24-hour period.

BNF Contraindications and Safety Warnings

The BNF lists several important contraindications for sildenafil. Patients taking nitrate medications (such as GTN spray or isosorbide mononitrate) must not use sildenafil due to potentially dangerous blood pressure drops. Other contraindications include severe cardiovascular disease, recent heart attack or stroke (within six months), severe liver impairment, and certain eye conditions. EverydayMeds offers both generic sildenafil and branded Viagra options, allowing patients to choose their preferred treatment following clinical assessment.

Drug Interactions Listed in BNF

The BNF highlights several significant drug interactions with sildenafil. Alpha-blockers used for prostate conditions may cause blood pressure reduction when combined with sildenafil. Certain antibiotics, antifungals, and HIV medications can increase sildenafil levels in the blood, potentially requiring dose adjustments. Patients should always inform their prescriber about all medications they're taking, including over-the-counter medicines and herbal supplements.

BNF Administration and Monitoring

According to BNF guidance, sildenafil should be taken on an empty stomach when possible, as fatty meals may delay absorption. The medication typically becomes effective within 30-60 minutes and effects may last up to four hours. However, this doesn't mean an erection will last this duration - sexual stimulation is still required for the medication to work. Regular monitoring may be necessary for patients with underlying health conditions or those taking multiple medications.

What you need to know about erectile dysfunction

It's one of the most common conditions we treat, and one of the most treatable.

What is Erectile Dysfunction?
ED means finding it hard to get or keep an erection firm enough for sex. It's not unusual to have an off night; the point at which it's worth doing something is when it's happening regularly, or when it's starting to bother you.
How will I feel when I take ED medication?
For most men, nothing feels different day to day. The medication works in the background — when you're sexually aroused, it helps blood flow where it's needed, so erections come more easily and last longer. It doesn't cause arousal on its own. Some men notice mild, short-lived effects like a headache, facial flushing or a stuffy nose, which usually pass as the dose wears off.
Why do I need a prescription for ED medication?
ED treatments are prescription-only medicines in the UK because they aren't suitable for everyone — for example, alongside certain heart conditions or medications like nitrates. That's why we ask you to complete a short online consultation first. A UK-registered prescriber reviews your answers to make sure your chosen treatment is safe and right for you before it's dispensed.
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