Our Pricing

Sildenafil BNF Safety Profile & Clinical Information

Understanding the sildenafil bnf safety profile uk is essential for safe and effective erectile dysfunction treatment. At Cured Pharmacy, our UK-registered clinical team follows British National Formulary guidance to ensure every prescription meets rigorous safety standards, with transparent pricing from £0.45 per dose and comprehensive clinical assessment before dispensing.

Sildenafil BNF Classification and Mechanism of Action

Sildenafil is classified in the BNF under section 7.4.5 as a phosphodiesterase type-5 (PDE5) inhibitor licensed for erectile dysfunction and pulmonary arterial hypertension [1]. The medication works by selectively inhibiting PDE5 in the corpus cavernosum, enhancing nitric oxide-mediated smooth muscle relaxation and increasing blood flow to penile tissues during sexual stimulation.

The BNF notes that sildenafil does not cause erections without sexual arousal, as the mechanism requires endogenous nitric oxide release [1]. Clinical trials demonstrate that approximately 70-80% of men with erectile dysfunction experience improved erectile function with sildenafil treatment, though individual response varies based on underlying aetiology and cardiovascular health [2].

BNF-Listed Contraindications for Sildenafil

The British National Formulary identifies several absolute contraindications where sildenafil must not be prescribed. These include concurrent use of nitrate medications or nicorandil, recent stroke or myocardial infarction (within 6 months), unstable angina, hypotension (blood pressure below 90/50 mmHg), and severe hepatic impairment [1][3].

Patients with hereditary degenerative retinal disorders, including retinitis pigmentosa, should not take sildenafil due to theoretical risk of retinal damage. The BNF also contraindicates use in patients with previous non-arteritic anterior ischaemic optic neuropathy (NAION), as PDE5 inhibitors may increase recurrence risk [1].

Cardiovascular Risk Assessment

The BNF emphasises cardiovascular risk stratification before prescribing sildenafil. Patients with significant cardiovascular disease require careful assessment, as sexual activity itself carries cardiac demand equivalent to moderate physical exertion [3]. Our UK prescribers at Cured Pharmacy conduct thorough cardiovascular screening during every clinical consultation to ensure sildenafil is appropriate for your individual health profile.

Sildenafil Dosage and Administration Per BNF Guidance

BNF-recommended initial dosing for erectile dysfunction is sildenafil 50mg taken approximately one hour before sexual activity, with dose adjustments based on efficacy and tolerability [1]. The dose may be increased to 100mg or decreased to 25mg depending on individual response. Maximum recommended dosing frequency is once daily.

For patients over 65 years, those with hepatic impairment, or those taking certain CYP3A4 inhibitors, the BNF recommends starting with 25mg to minimise adverse effects [1]. Sildenafil should be taken on an empty stomach when possible, as high-fat meals can delay absorption and reduce peak plasma concentrations by up to 29% [4].

Duration of Action and Timing

Sildenafil reaches peak plasma concentration within 30-120 minutes of oral administration, with clinical effects lasting approximately 4-6 hours in most patients [4]. The BNF notes that whilst the medication remains detectable in plasma for longer periods, erectile response to sexual stimulation typically diminishes after 4 hours. Patients should plan timing accordingly and avoid exceeding the maximum daily dose.

BNF-Documented Drug Interactions with Sildenafil

The British National Formulary highlights critical drug interactions that UK prescribers must consider. Concurrent nitrate use represents the most serious interaction, potentially causing life-threatening hypotension due to additive vasodilatory effects [1][3]. This contraindication extends to all nitrate formulations including glyceryl trinitrate, isosorbide mononitrate, and recreational nitrites (poppers).

CYP3A4 inhibitors significantly increase sildenafil plasma concentrations. The BNF lists ritonavir, saquinavir, ketoconazole, itraconazole, and erythromycin as requiring dose reduction to 25mg [1]. Alpha-blockers used for benign prostatic hyperplasia may cause symptomatic hypotension when initiated alongside sildenafil, and the BNF recommends stabilising alpha-blocker therapy before introducing PDE5 inhibitors.

Interactions with Other Erectile Dysfunction Treatments

The BNF explicitly contraindicates combining sildenafil with other PDE5 inhibitors such as tadalafil or vardenafil, as this provides no additional benefit and increases adverse effect risk [1]. Similarly, concurrent use with other erectile dysfunction treatments including alprostadil requires specialist supervision due to limited safety data.

Common and Serious Adverse Effects in the BNF

The BNF categorises sildenafil adverse effects by frequency and severity. Very common side effects (occurring in more than 1 in 10 patients) include headache and flushing, whilst common effects (1 in 10 to 1 in 100) encompass dyspepsia, nasal congestion, dizziness, and visual disturbances including altered colour perception [1][2].

Serious adverse effects are uncommon but require immediate medical attention. These include priapism (erection lasting over 4 hours), sudden vision loss potentially indicating NAION, sudden hearing loss, and cardiovascular events such as myocardial infarction or arrhythmias [1]. The BNF notes that whilst cardiovascular events have been reported during sildenafil use, causality is difficult to establish given the underlying cardiovascular risk factors in the patient population.

BNF Guidance on Special Populations and Monitoring

The British National Formulary provides specific guidance for prescribing sildenafil in special populations. Elderly patients (over 65 years) may experience higher plasma concentrations due to reduced hepatic metabolism and renal clearance, warranting initial dose reduction to 25mg [1]. Patients with moderate hepatic impairment (Child-Pugh class B) similarly require 25mg starting doses.

Renal impairment does not typically require dose adjustment unless creatinine clearance falls below 30 mL/min, where 25mg initial dosing is recommended [1]. The BNF emphasises that sildenafil is not licensed for use in women or children under 18 years for erectile dysfunction. Regular monitoring is not routinely required for stable patients, though cardiovascular risk should be reassessed if clinical circumstances change [3].

Patient Counselling Per BNF Recommendations

The BNF recommends comprehensive patient counselling covering timing of administration, recognition of serious adverse effects requiring urgent medical attention, and the absolute contraindication with nitrate medications [1]. At Cured Pharmacy, our UK-registered clinical team ensures every patient receives detailed safety information and understands when to seek immediate medical help, particularly for priapism or sudden vision changes.

Scientific References

1. British National Formulary. (2024). Sildenafil. BNF Online. London: BMJ Group and Pharmaceutical Press. https://bnf.nice.org.uk/drug/sildenafil.html
2. Goldstein, I., Lue, T. F., Padma-Nathan, H., Rosen, R. C., Steers, W. D., & Wicker, P. A. (1998). Oral sildenafil in the treatment of erectile dysfunction. New England Journal of Medicine, 338(20), 1397-1404. https://doi.org/10.1056/NEJM199805143382001
3. Jackson, G., Rosen, R. C., Kloner, R. A., & Kostis, J. B. (2006). The second Princeton consensus on sexual dysfunction and cardiac risk: new guidelines for sexual medicine. Journal of Sexual Medicine, 3(1), 28-36. https://doi.org/10.1111/j.1743-6109.2005.00196.x
4. Nichols, D. J., Muirhead, G. J., & Harness, J. A. (2002). Pharmacokinetics of sildenafil after single oral doses in healthy male subjects: absolute bioavailability, food effects and dose proportionality. British Journal of Clinical Pharmacology, 53(Suppl 1), 5S-12S. https://doi.org/10.1046/j.0306-5251.2001.00027.x

Information on this page is for educational purposes only and is not medical advice. All prescription treatments require clinical assessment by a UK-registered prescriber. Always consult a qualified healthcare professional before starting any new medication. The content reflects British National Formulary guidance current at time of writing but should not replace professional medical consultation.