Viagra

Viagra is the original brand-name treatment for erectile dysfunction (ED), manufactured by Pfizer and containing sildenafil citrate as its active ingredient. Recognisable worldwide by its iconic blue diamond-shaped tablets, Viagra is available in three strengths - 25mg, 50mg, and 100mg - and has been prescribed to tens of millions of men globally since its introduction in 1998. It belongs to a class of medicines known as phosphodiesterase type-5 (PDE5) inhibitors and works by enhancing the natural physiological response to sexual stimulation.

How Viagra Works

Erectile function depends on the relaxation of smooth muscle in the corpus cavernosum of the penis, which allows blood to flow in and create an erection. This relaxation is mediated by nitric oxide (NO), which activates an enzyme that produces cyclic guanosine monophosphate (cGMP). cGMP causes smooth muscle relaxation and vasodilation, increasing blood flow to the penis. The enzyme PDE5 naturally breaks down cGMP, limiting the duration of this effect. Sildenafil inhibits PDE5, preventing the breakdown of cGMP, prolonging smooth muscle relaxation, and facilitating a firmer, longer-lasting erection in response to sexual arousal. Crucially, Viagra does not cause an erection in the absence of sexual stimulation.

Who Can Benefit from Viagra

Viagra is indicated for adult men with erectile dysfunction of any aetiology, whether predominantly psychogenic, organic (vascular, neurological, or hormonal), or mixed. It is equally effective across a broad range of ages and in men with common comorbidities such as diabetes and hypertension. Sildenafil is also used at lower doses under the brand name Revatio for the treatment of pulmonary arterial hypertension. Brand-name Viagra carries the assurance of consistent pharmaceutical quality from Pfizer, though licensed generic sildenafil products are also available and contain the same active ingredient at equivalent doses.

Onset and Duration

Viagra should be taken approximately 30 to 60 minutes before anticipated sexual activity. The effect typically lasts for four to six hours, although this can vary between individuals. A heavy or high-fat meal taken immediately before Viagra can delay its absorption and onset of action by up to one hour. Alcohol in moderate to large quantities can both impair erectile function independently and may amplify the blood pressure-lowering effect of sildenafil, so intake should be moderated.

Viagra is taken on an as-needed basis, approximately 30 to 60 minutes before sexual activity. It is not intended to be taken daily as a regular dose; rather, it is used when required, with no more than one dose per 24-hour period.

How to Take Viagra Correctly

Swallow the tablet whole with a glass of water. Avoid taking Viagra with grapefruit or grapefruit juice, as grapefruit inhibits the CYP3A4 enzyme responsible for metabolising sildenafil and can lead to significantly elevated drug levels and an increased risk of side effects. A light meal beforehand is preferable to a heavy, fatty one, as high-fat food can delay absorption. Sexual stimulation is required for the medicine to work; sildenafil alone will not produce an erection.

Starting Dose and Adjustment

The recommended starting dose for most men is 50mg. If this dose is effective but causes troublesome side effects, the 25mg strength may be used. If 50mg is insufficient after a fair trial, the dose may be increased to 100mg, which is the maximum recommended dose. Do not take more than 100mg in any 24-hour period. Men aged 65 and over are typically started on 25mg, and those with significant renal or hepatic impairment should also start at the lower dose. If Viagra is not effective after several attempts at the highest tolerated dose, seek review from your doctor.

The recommended starting dose is 50mg taken approximately 30 to 60 minutes before sexual activity, on an as-needed basis, with no more than one dose per day.

Dose range: 25mg to 100mg. The 25mg dose is recommended for patients aged 65 or over, those with significant renal impairment (CrCl below 30 mL/min), those with mild to moderate hepatic impairment, and those taking CYP3A4 inhibitors such as erythromycin or saquinavir. The maximum dose is 100mg per 24 hours. Viagra must not be taken by anyone using nitrates in any form, as the combination can cause a sudden and severe drop in blood pressure.

Common Side Effects

• Headache
• Facial flushing
• Nasal congestion or runny nose
• Indigestion or dyspepsia
• Dizziness
• Visual disturbances (blue-tinged vision, increased light sensitivity)
• Back pain
• Muscle aches

Serious Side Effects

• Sudden loss of vision in one or both eyes (non-arteritic anterior ischaemic optic neuropathy - NAION): stop use and seek emergency care
• Sudden hearing loss or tinnitus: stop use and seek urgent medical attention
• Priapism (a painful erection lasting more than four hours): requires emergency medical treatment to prevent permanent damage
• Severe hypotension, especially if combined with nitrates or alpha-blockers - this combination is absolutely contraindicated
• Severe allergic reaction (angioedema, anaphylaxis)

Viagra carries several critically important safety warnings that must be understood before use.

Absolute Contraindication with Nitrates

The combination of sildenafil with any nitrate medicine is absolutely contraindicated and potentially life-threatening. Nitrates, which include glyceryl trinitrate (GTN) sprays, nitroglycerin patches, isosorbide mononitrate, and isosorbide dinitrate, are used to treat angina. Both nitrates and PDE5 inhibitors lower blood pressure via nitric oxide pathways, and their combination causes an additive and unpredictable drop in blood pressure that can result in fainting, myocardial infarction, or death. Any man who uses nitrates in any form, including amyl nitrite ('poppers'), must not take Viagra. A minimum interval of 24 hours is required between the last dose of sildenafil and use of a nitrate, though some guidelines recommend longer intervals.

Cardiovascular Risk and Vision or Hearing

Sexual activity itself places demands on the cardiovascular system. Viagra should be used with caution in men who have had a recent heart attack or stroke, those with severe cardiac failure, unstable angina, or poorly controlled hypertension, and those for whom sexual activity is inadvisable on cardiovascular grounds. Rare cases of sudden vision loss and sudden hearing loss have been reported in men taking PDE5 inhibitors; while a direct causal link has not been definitively established, patients should stop Viagra immediately and seek urgent assessment if they experience either symptom.

• Current or recent use of any nitrate medicine in any form (including amyl nitrite/'poppers') - absolute contraindication
• Known hypersensitivity to sildenafil or any excipient
• Severe hepatic impairment (Child-Pugh C)
• Recent history (within 90 days) of myocardial infarction
• Stroke or life-threatening arrhythmia within the last six months
• Resting hypotension (blood pressure below 90/50 mmHg)
• Severe uncontrolled hypertension (blood pressure above 170/100 mmHg)
• Loss of vision in one eye due to NAION
• Concurrent use of ritonavir or saquinavir (potent CYP3A4 inhibitors) at doses above 25mg
• Use of guanylate cyclase stimulators (e.g. riociguat)