Sildenafil citrate, sold as Viagra, Revatio and under various other trade names, is a drug used to treat erectile dysfunction and pulmonary arterial hypertension (PAH). It was originally developed by British scientists and then brought to market by the US-based pharmaceutical company Pfizer. It acts by inhibiting cGMP-specific phosphodiesterase type 5, an enzyme that promotes degradation of cGMP, which regulates blood flow in the penis. Since becoming available in 1998, sildenafil has been the prime treatment for erectile dysfunction; its primary competitors on the market are tadalafil (Cialis) and vardenafil (Levitra).visit more in weigesc
枸橼酸西地那非（Sildenafil citrate）又名昔多芬，一氧化氮样药物。商品名有Viagra（万艾可/伟哥）、Revatio（瑞肺得）等。是用于ED（男性勃起障碍/阳痿）和PAH（肺动脉高压）的药物。它首先是英国科学家发明，由美国辉瑞（Pfizer）制药公司推向市场的。西地那非是一种PDE5抑制剂（cGMP-specific phosphodiesterase type 5，5型磷酸二酯酶抑制剂）。通过抑制降解cGMP的5型磷酸二酯酶活性而增高细胞内cGMP浓度，导致平滑肌松弛，使阴茎海绵体内动脉血流增加，产生勃起。自1998年上市后，西地那非成为ED的首选药物。其他的竞争药物有他达拉非tadalafil（Cialis，希力士）和伐地那非vardenafil（Levitra，艾力达）。Medical uses
药物作用
Sexual dysfunction
性功能障碍
枸橼酸西地那非片功效效及作用The primary indication of sildenafil is treatment of erectile dysfunction (inability to sustain a satisfactory erection to complete intercourse). Its use is now standard treatment for erectile dysfunction in all settings, including diabetes.
西地那非是阳痿（无法保持满意的勃起状态而无法完成性交活动）的首选药物。如今它是由各种疾病，包括糖尿病导致ED（阳痿）的标准药物。
People on antidepressants may experience sexual dysfunction, either as a result of their illness or as a result of their treatment. A 2003 study showed that sildenafil improved sexual function in men in this situation. Following up reports from 1999, the same researchers found that sildenafil improved sexual function in female patients on antidepressants as well.
服用抗抑郁剂可能导致勃起障碍，不过抑郁症也会引起ED。2003年的一项研究表明，西地那非能够改善男性的勃起障碍。值得一提的是，该项研究的研究者们早在1999年就发现，西地那非能够提高服用抗抑郁药的女性患者的性欲。
Pulmonary hypertension
肺动脉高压
As well as erectile dysfunction, sildenafil citrate is also effective in the rare disease pulmonary arterial hypertension (PAH). It relaxes the arterial wall, leading to decreased pulmonary arterial resistance and pressure. This, in turn, reduces the workload of the right ventricle of the heart and improves symptoms of right-sided heart failure. Because PDE-5 is primarily distributed within the arterial wall smooth muscle of the lungs and penis, sildenafil acts selectively in both these areas without inducing vasodilation in other areas of the body. Pfizer submitted an additional registration for sildenafil to the FDA, and sildenafil was approved for this indication in June 2005. The preparation is named Revatio, to avoid confusion with Viagra, and the 20 milligram tablets are white and round. Sildenafil joins bosentan and prostacyclin-based therapies for this condition.
西地那非还用于罕见的肺动脉高压。它可以扩张动脉血管，降低肺动脉的抵抗力和压力，从而减轻右心室的工作负荷和改善右心力衰竭（right-sided heart failure）。因为PDE-5（5型磷酸二酯酶）
主要分布于肺部动脉平滑肌和阴茎。西地那非选择性地作用于这些区域，而不会引起身体其他区域的血管舒张。2005年6月，美国FDA批准一种西地那非制剂用于肺动脉高压，为避免和Viagra（万艾可）混淆，其商品名为Revatio（瑞肺得），且剂量为20mg的白圆状片剂。（译者注：万艾可为蓝
薄膜包衣的圆棱形片剂，剂量有25、50、100mg三种）。西地那非常联合波生坦（bosentan）和前列环素类药物PAH。
Altitude sickness
高空病/高原病
Sildenafil has been shown to be useful for the prevention and treatment of high-altitude pulmonary edema associated with altitude sickness such as that suffered by mountain climbers. While this effect has only recently been discovered, sildenafil is already becoming an accepted treatment for this condition, in particular in situations where the standard treatment of rapid descent has been delayed for some reason.
由于在高空中空气稀薄导致血液及组织缺氧所产生的反应（如头痛、倦怠、心悸、鼻出血、恶心）。西地那非已经证明可以预防和高空肺水肿。
Dosage
给药剂量
Viagra pills are blue and diamond-shaped with the word "Pfizer" engraved on one side, and "VGR xx" (where xx stands for "25", "50" or "100", the dose of that pill in milligrams) engraved on the other. It is not taken more than once per day between 30 minutes and 4 hours prior to sexual intercourse.
万艾可/伟哥是一种蓝薄膜包衣的圆棱形片剂，一面刻有“Pfizer”字样，另一面为“VGR xx”（XX有3种，分别为25、50、100，单位为mg）。一天最多只能服用1次，性爱活动前30分钟～4小时口服。
The dosage for pulmonary arterial hypertension (Revatio) is three times a day. Revatio pills are white, round, film-coated tablets imprinted with "RVT 20" embossed on one side.
Revatio（瑞肺得）是一种白薄膜包衣的圆状片剂。“RVT 20”字样则凸出药片的表面。用法为一天3次。
Adverse effects
副作用
In clinical trials, the most common adverse effects of sildenafil use included headache, flushing, dyspepsia, nasal congestion and impaired vision, including photophobia and blurred vision.Some sildenafil users have complained of seeing everything tinted blue (cyanopsia).Some complained of bl
urriness and loss of peripheral vision. In July 2005, the U.S. Food and Drug Administration found that sildenafil could lead to vision impairment in rare cases and a number of studies have linked sildenafil use with nonarteritic anterior ischemic optic neuropathy.
临床试验中，最常见的副作用有头疼、脸红、消化不良、鼻充血和视觉异常，包括畏光和视物模糊。一些服用者会出现蓝视（即看到东西带有蓝的彩）、视觉模糊或周边视觉的现象。2005年7月，美国FDA发现西地那非罕见的副作用——视力损伤，另外若干研究表明使用西地那非和前部缺血性视神经病有着相关性。
Rare but serious adverse effects found through postmarketing surveillance include priapism, severe hypotension, myocardial infarction (heart attack), ventricular arrhythmias, stroke, increased intraocular pressure, and sudden hearing loss. As a result of these postmarketing reports, in October 2007, the FDA announced that the labeling for all PDE5 inhibitors, including sildenafil, required a more prominent warning of the potential risk of sudden hearing loss.
通过药物售后监察发现罕见且严重的副作用有阴茎持续勃起、严重低血压、心肌梗死、室性心律失常、中风、眼内压增高和突发性耳聋。2007年10月，FDA要求所有的PDE5抑制剂，包括西地那非需标记可能会导致潜在突发性耳聋的风险。
Interactions
药物的相互作用
Care should be exercised by patients that are also taking protease inhibitors for the treatment of HIV. Protease inhibitors inhibit the metabolism of sildenafil, effectively multiplying the plasma levels of sildenafil, increasing the incidence and severity of side effects. It is recommended that patients using protease inhibitors limit their use of sildenafil to no more than one 25 mg dose every 48 hours. Other drugs that interfere with the metabolism of sildenafil include erythromycin and cimetidine, both of which can also lead to prolonged plasma half life levels.
Concomitant use of sildenafil and an alpha blocker may lead to low blood pressure, but this effect does not occur if they are taken at least four hours apart.
服用蛋白酶抑制剂（Protease inhibitors）HIV的患者需要特别的注意。蛋白酶抑制剂会抑制西地那非的新陈代谢，增加血浆水平结合率，可能造成以外和严重的副反应。故药物专家推荐48小时内最多只能服用25mg。其他会干扰西地那非代谢的药物有甲氰咪胺（cimetidine，胃黏膜保护药）、红霉素（erythromycin）会增加血浆半衰期（plasma half-life）水平。
西地那非和α受体阻断药物一起使用可能造成血压过低。不过两者间隔4个小时服用则不会发生。
Contraindications
禁忌症
Contraindications include: When taking nitric oxide donors, organic nitrites and nitrates, such as glyceryl trinitrate (nitroglycerin), sodium nitroprusside, amyl nitrite ("poppers")
服用任何硝酸盐类药物。如、硝普钠、亚硝酸戊酯等
In men for whom sexual intercourse is inadvisable due to cardiovascular risk factors
身体条件不适宜过性生活，如严重的心脏病
Severe hepatic impairment (decreased liver function)
严重的肝损伤（肝功能不足）
Severe impairment in renal function
严重的肾损伤（肾功能不足）
Hypotension (low blood pressure)
低血压
Recent stroke or heart attack
最近发生过中风或心脏病
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Hereditary egenerative retinal disorders,including genetic disorders of retinal phosphodiesterases 遗传性视网膜退化症（包括遗传性视黄醛磷酸二酯酶失调）