Sildenafil is a medication used to treat certain cardiovascular and urological conditions, primarily functioning by inhibiting phosphodiesterase-5 (PDE5). Originally developed for pulmonary arterial hypertension (PAH), it was later expanded to include erectile dysfunction (ED) after clinical observations demonstrated efficacy in improving male erectile function. Its mechanism involves vasodilation, increasing blood flow, thereby enhancing oxygen supply to organs or promoting penile blood engorgement.
In clinical practice, sildenafil is approved for the treatment of erectile dysfunction (ED) and specific types of pulmonary arterial hypertension (PAH). For ED patients, the medication must be used in conjunction with sexual stimulation; for PAH patients, it requires long-term regular administration to improve cardiopulmonary function. Available formulations include oral tablets, which should be used according to medical advice without self-adjusting the dose.
The generic name of this medication is "Sildenafil," with the international non-proprietary name being Sildenafil Citrate. Common brand names include "Viagra" and "Revatio," where the former is mainly used for erectile dysfunction, and the latter for pulmonary arterial hypertension. Different regions may have other brand names, but the generic name and main active ingredient remain the same.
Patients should verify that the active ingredient on the medication label is "Sildenafil" when purchasing or using, and note that different dosages and packaging may be indicated for different conditions. Physicians will select the appropriate formulation and brand based on the patient's specific condition.
Sildenafil is classified as a "Phosphodiesterase-5 (PDE5) inhibitor." These drugs selectively inhibit PDE5, increasing the levels of cyclic guanosine monophosphate (cGMP) induced by nitric oxide (NO). This mechanism makes it suitable for treating peripheral vascular diseases such as ED and pulmonary arterial hypertension (PAH).
The key feature of this drug class is its selectivity for PDE5, which prevents widespread effects on other phosphodiesterases in different tissues, reducing the risk of side effects. This characteristic makes it one of the preferred medications for treating certain vascular constriction-related diseases.
The primary indications for sildenafil include:
For ED patients, the medication must be used with sexual stimulation; for PAH patients, it can improve exercise tolerance and hemodynamic parameters.
Additionally, in clinical practice, it is occasionally used for other unapproved indications, such as adjunct therapy for PAH post-cardiac surgery, but this requires risk assessment by a physician. Unauthorized use beyond approved indications is not advised without medical supervision.
Common mild side effects include:
These reactions are usually transient, dose-related, and most patients can manage them independently.
Serious side effects requiring immediate medical attention include:
If any of the above symptoms occur, discontinue the medication immediately and seek medical assistance.
Strictly avoid concurrent use with nitrates (e.g., nitroglycerin), as this can cause life-threatening hypotension. This contraindication is a black-box warning, and patients should inform their healthcare provider of all medications they are taking, including cardiac drugs, prior to use.
Pregnant women or women who may become pregnant should not use sildenafil, as animal studies suggest potential effects on fetal development, and human safety data are lacking. Patients with cardiovascular disease should evaluate cardiac function before use, as sexual activity may increase cardiac workload.
Concurrent use with nitrates (e.g., angina medications) can cause fatal hypotension, representing the most severe drug interaction. When combined with alpha-blockers (e.g., medications for prostate enlargement), dose reduction is necessary to prevent excessive blood pressure lowering.
Use with HIV protease inhibitors (e.g., ketoconazole, itraconazole) may prolong sildenafil half-life, increasing the risk of side effects. Consult a healthcare provider before taking any herbal supplements or over-the-counter products (e.g., folic acid, ginkgo), as they may affect drug metabolism.
The recommended starting dose for erectile dysfunction is 50 mg, adjustable to 25-100 mg based on response, taken no more than once daily, 30 minutes before sexual activity. For PAH, doses are typically 20 mg or 40 mg twice daily, taken at fixed times to maintain consistent blood levels.
The medication can be taken on an empty stomach or with a low-fat meal; high-fat meals may delay absorption. Tablets should be swallowed whole; do not chew or split. Pediatric dosing is based on weight and is limited to PAH treatment under medical supervision.
If a dose for ED is missed, take it as soon as remembered, but if less than 4 hours remain before the next scheduled dose, skip the missed dose and resume normal dosing the following day. Do not double doses to compensate.
For PAH, if a scheduled dose is missed, take it immediately and adjust the next dose time to avoid large fluctuations in blood levels. If more than 4 hours are missed, continue with the regular schedule without doubling the dose.
Overdose may cause severe hypotension, visual disturbances, or prolonged erections. If overdose is suspected, seek immediate medical attention and bring the medication container. Hospital treatments may include gastric lavage or specific antidotes.
A prolonged erection exceeding 4 hours (priapism) must be treated as a medical emergency. Delay in treatment can lead to tissue necrosis and permanent damage, requiring urgent hospital intervention.
Does high-fat food intake affect the efficacy of sildenafil?
High-fat meals may delay drug absorption. It is recommended to take the medication on an empty stomach or after a light meal to ensure optimal effect. If taken with a high-fat meal, some efficacy may still be achieved, but onset may be delayed. Patients are advised to maintain consistent timing and dietary habits to stabilize drug effects.
What should I do if I experience dizziness or visual disturbances while using sildenafil?
Dizziness may result from blood pressure drops; avoid sudden standing or excessive activity during initial use. If symptoms such as blue vision or light sensitivity occur, stop the medication and seek medical attention, as these may indicate interactions with nitrates. Mild dizziness is usually temporary and can be alleviated with rest.
What precautions should be taken when using sildenafil with antihypertensive medications?
Concurrent use with nitrates (e.g., nitroglycerin) can cause severe hypotension and life-threatening side effects, and must be avoided. When used with other antihypertensives (e.g., ACE inhibitors, calcium channel blockers), the physician will adjust doses based on blood pressure control. Patients should inform their healthcare provider of all medications they are taking.
Does long-term regular use of sildenafil lead to increased drug tolerance?
Current studies suggest that intermittent use (e.g., 3-4 times weekly) generally does not cause significant tolerance. Overuse (e.g., multiple times daily) may reduce effectiveness. It is recommended to use the medication on an as-needed basis. If effectiveness diminishes, consult a healthcare provider to evaluate potential vascular disease progression or other health issues.
Can sildenafil be used to treat pulmonary arterial hypertension? How does its mechanism differ from that for erectile dysfunction?
Yes, sildenafil is also approved for PAH treatment, but the dosage and frequency differ from those for ED. In PAH, it selectively inhibits PDE5, promoting relaxation of pulmonary vascular smooth muscle via nitric oxide, thereby reducing pulmonary vascular resistance over time. This use requires adherence to specialized prescriptions and should not be self-adjusted.
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