Sildenafil

Sildenafil is a drug from the group of PDE-5 inhibitors that is used to treat erectile dysfunction. The active ingredient was originally developed by Pfizer and became known under the brand name Viagra®. Since the patent expired in 2013, sildenafil has also been available as a generic from various manufacturers.

The medication makes an erection possible during sexual stimulation by improving blood flow to the penis. Without sexual arousal, sildenafil has no effect – so it is not an aphrodisiac.

Sildenafil generics contain the same active ingredient as the original product and are subject to the same strict quality requirements.

Sildenafil belongs to the drug class of phosphodiesterase-5 inhibitors (PDE-5 inhibitors). To understand how it works, a brief look at the mechanism of erection is helpful:

During sexual arousal, the messenger substance nitric oxide (NO) is released in the erectile tissue of the penis. This activates an enzyme that leads to the formation of cyclic guanosine monophosphate (cGMP). cGMP causes the smooth muscle in the blood vessels of the penis to relax – as a result, more blood flows in and an erection develops.

The enzyme phosphodiesterase-5 (PDE-5) normally breaks down cGMP again, thereby ending the erection. Sildenafil inhibits this enzyme so that cGMP remains active for longer. The result: an erection can develop more easily and be maintained for longer.

Important: Sildenafil only works when sexual stimulation is present. Without arousal, no nitric oxide is released, and the medication cannot take effect.

Sildenafil is suitable for adult men with erectile dysfunction, i.e., the recurring inability to achieve or maintain an erection sufficient for sexual intercourse.

Typical areas of use:

• Erection problems due to circulatory disorders
• Erectile dysfunction in diabetes mellitus
• Psychologically caused erection problems
• Erection problems as a concomitant symptom of other diseases

Before use, the following should be clarified:

• The cause of the erection problems (organic, psychological, or mixed)
• Whether cardiovascular diseases are present
• Which other medications are being taken
• Whether any contraindications exist

Sildenafil is available in various strengths:

Common dosages:

• 25 mg – Lowest dose, suitable for men over 65 years of age or with impaired liver/kidney function
• 50 mg – Standard dose for starting treatment
• 100 mg – Highest approved single dose

Recommendation for finding the right dose: The usual starting dose is 50 mg. Depending on efficacy and tolerability, the dose can be increased to 100 mg or reduced to 25 mg. The maximum dose of 100 mg per day should not be exceeded.

Pack sizes: Sildenafil is available in packs of 4, 8, 12, or 24 tablets. The tablets can usually be divided, which allows flexible dosing.

When to take it: Sildenafil should be taken about 30 to 60 minutes before planned sexual intercourse. The effect can begin after as little as 30 minutes.

Taking it with or without food: The tablet can be taken regardless of meals. However, a high-fat meal can delay the onset of action. For a faster effect, taking it on an empty stomach or after a light meal is recommended.

Duration of action: The effect of sildenafil lasts about 4 to 6 hours. During this period, an erection is possible with sexual stimulation.

Frequency: Sildenafil should be taken no more than once a day. At least 24 hours should pass between two doses.

Alcohol: Small amounts of alcohol are generally possible, but can impair effectiveness and increase the risk of side effects.

Sildenafil must not be taken in cases of:

• Use of nitrates or NO donors – these include glyceryl trinitrate (nitroglycerin spray), isosorbide mononitrate, isosorbide dinitrate, and amyl nitrite (poppers). The combination can lead to a life-threatening drop in blood pressure.

• Use of guanylate cyclase stimulators such as riociguat – the combination can lead to a drop in blood pressure with symptoms.

• Severe cardiovascular diseases – especially unstable angina pectoris, severe heart failure, or a recent heart attack or stroke

• Low blood pressure (below 90/50 mmHg)

• Severe liver impairment

• Certain eye diseases – especially hereditary retinal diseases such as retinitis pigmentosa

• Loss of vision in one eye due to NAION (non-arteritic anterior ischemic optic neuropathy) – regardless of whether the vision loss was related to previous use of a PDE-5 inhibitor

• Hypersensitivity to sildenafil or any of the other ingredients

Caution is required in cases of:

• Anatomical changes of the penis
• Conditions that may be associated with prolonged erection (e.g., sickle cell anemia)
• Blood clotting disorders or active stomach ulcers

Like all medicines, sildenafil can cause side effects. Most side effects are mild to moderate and go away on their own.

Very common (more than 1 in 10):

• Headache

Common (1 to 10 in 100):

• Facial redness (flushing)
• Stuffy nose
• Indigestion
• Nausea
• Dizziness
• Visual disturbances (e.g., bluish tinge to vision, increased sensitivity to light)

Uncommon (1 to 10 in 1000):

• Racing heart
• Tiredness
• Skin rash

Rare but serious:

• Priapism (painful erection lasting more than 4 hours) – immediate medical treatment required
• Sudden hearing loss or loss of vision – see a doctor immediately

Most side effects are dose-dependent and occur less often at lower doses.

Important interactions:

• Nitrates and NO donors: Absolutely contraindicated! The combination can cause a dangerous drop in blood pressure.

• Alpha blockers: Taking them at the same time can increase the blood-pressure-lowering effect. Sildenafil should only be started once alpha-blocker therapy is stable.

• CYP3A4 inhibitors: Medications such as ritonavir, ketoconazole, itraconazole, and erythromycin can increase the concentration of sildenafil in the blood. A starting dose of 25 mg should be considered. Concomitant use with ritonavir is not recommended; if ritonavir is taken nonetheless, the sildenafil dose must never exceed 25 mg within 48 hours.

• Other PDE-5 inhibitors: No concomitant use with tadalafil, vardenafil, or avanafil.

• Grapefruit juice: Can slightly increase the concentration of the active ingredient.

• Blood-pressure-lowering medications: Can increase the blood-pressure-lowering effect of sildenafil.