Sildenafil is a medication used to treat specific cardiovascular and urological conditions, primarily working by inhibiting phosphodiesterase type 5 (PDE5). This drug was initially developed for the treatment of pulmonary arterial hypertension and later expanded its indications due to clinical observations of its efficacy in treating male erectile dysfunction. Its mechanism of action involves vasodilation, increasing blood flow, thereby improving oxygen supply to organs or promoting penile blood engorgement.
In clinical applications, sildenafil is approved for the treatment of erectile dysfunction (ED) and specific types of pulmonary arterial hypertension (PAH). For ED patients, this medication must be used in conjunction with sexual stimulation; for PAH patients, it must be taken regularly over the long term to improve cardiopulmonary function. The medication is available in oral tablet form and should be used according to medical advice, without self-adjusting the dosage.
The generic name of this medication is "Sildenafil," and its international nonproprietary name is Sildenafil Citrate. Common brand names include "Viagra" and "Revatio," with the former primarily used for erectile dysfunction and the latter targeting pulmonary arterial hypertension treatment. Different regions may have other brand names, but the generic name and active ingredients remain the same.
Patients should verify that the active ingredient on the medication label is "Sildenafil" when purchasing or using it and be aware that different dosages and packaging may have different indications. Doctors will choose the appropriate formulation and brand based on the patient's specific condition.
Sildenafil is classified as a "phosphodiesterase type 5 (PDE5) inhibitor," which selectively inhibits the PDE5 enzyme, increasing the concentration of cyclic guanosine monophosphate (cGMP) induced by nitric oxide (NO). This mechanism of action allows it to be used in treating peripheral vascular diseases (such as ED) and pulmonary arterial hypertension (PAH).
The key aspect of this drug classification is its selective action on PDE5, avoiding widespread effects on phosphodiesterases in other tissues, thus reducing the risk of side effects. This characteristic makes it one of the preferred medications for treating specific vascular constriction-related diseases.
The main indications for sildenafil include:
Additionally, this medication may occasionally be used in clinical practice for other unapproved indications, such as adjunctive treatment for pulmonary arterial hypertension after cardiac surgery, but this should only be done after a physician assesses the risks. Patients should not expand the use of the medication without a doctor's instruction.
Common mild side effects include:
Serious side effects requiring immediate medical attention include:
It is strictly prohibited to use this medication in combination with nitrate drugs (such as nitroglycerin), as it may lead to life-threatening hypotension. This contraindication is a black box warning, and patients must inform their doctor of all medications they are currently taking, including those for heart disease.
Pregnant or potentially pregnant women are prohibited from using this medication, as animal studies have shown potential effects on fetal development, and there is currently a lack of human safety data. Patients with cardiovascular diseases should have their heart function assessed before use, as sexual activity may increase cardiac load.
Using this medication with nitrate drugs (such as those for angina) may cause fatal hypotension, which is the most serious drug interaction. When used with alpha-blockers (such as medications for benign prostatic hyperplasia), the dosage should be reduced to avoid excessive blood pressure drop.
Using this medication with HIV protease inhibitors (such as ketoconazole, itraconazole) may prolong the half-life of sildenafil, increasing the risk of side effects. Patients should consult their doctor before taking any herbal medicines or supplements (such as folic acid, ginkgo), as they may affect drug metabolism.
The recommended starting dose for erectile dysfunction is 50 mg, adjusted to 25-100 mg based on response, taken no more than once daily, and should be taken 30 minutes before sexual activity. For pulmonary arterial hypertension patients, it is divided into doses of 20 mg or 40 mg taken twice daily, and the medication should be taken at fixed intervals to maintain blood drug concentration.
This medication can be taken on an empty stomach or with a low-fat meal; a high-fat diet may delay absorption. The tablet should be swallowed whole and not chewed or split. Pediatric dosing should be calculated based on body weight, limited to PAH indications and used under physician supervision.
If a dose for erectile dysfunction is missed, it should be taken as soon as remembered, but if it is less than 4 hours until the next dose, the missed dose should be skipped, and normal dosing should resume the next day. Do not double the dose to make up for a missed dose.
If a scheduled dose for pulmonary arterial hypertension is missed, it should be taken immediately and the timing of the next dose adjusted to avoid significant fluctuations in blood drug concentration. If more than 4 hours have passed, continue with the normal schedule without adding a dose.
Overdose may lead to severe hypotension, visual abnormalities, or prolonged erection. If overdose is suspected, seek medical attention immediately and bring the medication bottle for reference. Medical facilities may perform gastric lavage or use specific antidotes.
If an overdose results in an erection lasting more than 4 hours (symptoms of penile necrosis), it must be treated as a medical emergency. Delayed treatment may lead to tissue necrosis and permanent damage, requiring immediate treatment in an emergency room.
Will taking sildenafil after consuming high-fat foods affect its efficacy?
A high-fat diet may delay drug absorption, so it is recommended to take it on an empty stomach or after a light meal to ensure optimal effect. If inadvertently taken with a high-fat meal, it may still have some effect but may take longer to work. Patients are advised to maintain a consistent medication schedule and dietary pattern to stabilize drug efficacy.
What should be done if dizziness or visual abnormalities occur during sildenafil use?
Dizziness may be caused by a drop in blood pressure; it is advised to avoid sudden standing or excessive activity when using the medication for the first time. If rare visual symptoms such as blue vision or light sensitivity occur, the medication should be stopped immediately, and medical attention sought, as these may be warning signs of interactions with nitrate drugs. Mild dizziness is usually temporary and can be relieved by resting.
What precautions should patients using antihypertensive medications take when using sildenafil?
Using it with nitrates (such as nitroglycerin) will severely lower blood pressure and may cause life-threatening side effects; both must be avoided simultaneously. When using other classes of antihypertensive drugs (such as ACE inhibitors, Calcium Channel Blockers), the doctor will adjust the dosage based on blood pressure control, and patients must inform the doctor of all medications they are currently taking.
Will long-term regular use of sildenafil lead to increased drug tolerance?
Current studies show that intermittent use as directed (such as 3-4 times a week) usually does not lead to significant tolerance. However, excessive frequent use (such as multiple times daily) may reduce effectiveness; it is recommended to follow the "as needed" principle. If effectiveness gradually decreases, a follow-up visit should be made to assess potential worsening of vascular diseases or other health issues.
Can sildenafil be used to treat pulmonary arterial hypertension? How does its mechanism of action differ from that used for erectile dysfunction?
Yes, sildenafil is also approved for the treatment of pulmonary arterial hypertension, but the dosage and frequency of use differ from those for erectile dysfunction. In the treatment of pulmonary arterial hypertension, it promotes relaxation of vascular smooth muscle induced by nitric oxide through selective inhibition of phosphodiesterase-5, improving pulmonary vascular resistance over the long term. This use must follow specialized prescription instructions and should not be self-adjusted.
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