The molecular mechanism of
| Dosage Form | Strengths (mg) | Available Packaging | Typical Use Cases |
|---|---|---|---|
| Tablets | 25 | Blister packs of 4, 8 | Mild to moderate ED |
| Tablets | 50 | Blister packs of 4, 8 | Common dose, initial use |
| Tablets | 100 | Blister packs of 4, 8 | Severe ED issues |
smooth muscle relaxation involves
the enzyme CGMP-dependent protein kinase, also known as PKG.
| Medication | Generic Name | Onset of Action | Duration | Common Dosage | Notes |
|---|---|---|---|---|---|
| Viagra | Sildenafil citrate | 30-60 minutes | 4-6 hours | 50-100 mg | Most widely used ED drug |
| Cialis | Tadalafil | 30-60 minutes | Up to 36 hours | 10-20 mg | Longer-lasting effect |
| Levitra | Vardenafil | 25-60 minutes | 4-5 hours | 10-20 mg | Similar to Viagra, different formulation |
This kinase is activated by cGMP and
it phosphorylates multiple targets in the smooth
[33] The reasons behind such use include the belief that the drug increases libido, improves sexual performance,[33] or permanently increases penis size. [34] Studies on the effects of sildenafil when used recreationally are limited, but suggest it has little effect when used by those who do not have erectile dysfunction. In one study, a 25 mg dose was shown to cause no significant change in erectile quality, but did reduce the postejaculatory refractory time. [35] This study also noted a significant placebo effect in the control group. Unprescribed recreational use of sildenafil and other PDE5 inhibitors is noted as particularly high among users of illegal drugs.
[36] Sildenafil is sometimes used to counteract the effects of other substances, often illicit. [33] Some users mix it with methylenedioxymethamphetamine (MDMA, ecstasy), other stimulants, or opiates in an attempt to compensate for the common side effect of erectile dysfunction, a combination known as "sextasy", "rockin' and rollin'", "hammerheading", or "trail mix". [33] Mixing it with amyl nitrite, another vasodilator, is particularly dangerous and potentially fatal. The 2007 Ig Nobel Prize in aviation went to Patricia V. Agostino, Santiago A. muscle cells, namely myosin light chain phosphatase,
| Product | Dosage | Quantity + Bonus | Price | |
|---|---|---|---|---|
| Viagra Original | 100mg | 92 + 4 Pills | 362.88€ 345.60€ | |
| Viagra Soft Tabs | 100mg | 90 + 6 Pills | 205.31€ 195.53€ | |
| Viagra Original | 100mg | 14 + 2 Pills | 89.03€ 84.79€ | |
| Viagra Generic | 100mg | 30 + 4 Pills | 60.91€ 58.01€ | |
| Viagra Super Active | 100mg | 90 + 10 Pills | 165.61€ 157.72€ | |
| Viagra Generic | 25mg | 10 Pills | 25.19€ 23.99€ | |
| Viagra Professional | 100mg | 360 + 6 Pills | 527.09€ 501.99€ | |
| Viagra Generic | 25mg | 20 Pills | 37.74€ 35.94€ | |
| Viagra Generic | 50mg | 180 + 8 Pills | 158.82€ 151.26€ | |
| Viagra Soft Tabs | 100mg | 20 Pills | 62.99€ 59.99€ | |
| Viagra Professional | 100mg | 120 + 4 Pills | 262.83€ 250.31€ | |
| Viagra Super Active | 100mg | 120 + 16 Pills | 198.37€ 188.92€ | |
| Viagra Soft Tabs | 100mg | 180 + 10 Pills | 314.95€ 299.95€ | |
| Viagra Soft Tabs | 100mg | 30 + 4 Pills | 83.06€ 79.10€ | |
| Viagra Professional | 100mg | 90 + 2 Pills | 207.09€ 197.23€ | |
| Viagra Generic | 200mg | 20 Pills | 61.69€ 58.75€ | |
| Viagra Generic | 100mg | 90 + 6 Pills | 129.02€ 122.88€ |
RhoA, IP3 receptor, phospholipase C, and others.
[8] It can be taken orally (swallowed by mouth), intravenously (injection into a vein), or through the sublingual route (dissolved under the tongue). [8][10] Onset when taken orally is typically within twenty minutes and lasts for about two hours. Common side effects include headaches, heartburn, and flushed skin. [8] Caution is advised in those with cardiovascular disease. [8] Rare but serious side effects include vision problems, hearing loss, and prolonged erection (priapism) that can lead to damage to the penis.
[8] Sildenafil should not be taken by people on nitric oxide donors such as nitroglycerin, as this may result in a serious drop in blood pressure. Sildenafil acts by blocking phosphodiesterase 5 (PDE5), an enzyme that promotes breakdown of cGMP, which regulates blood flow in the penis. [8] It requires sexual arousal to work, and does not by itself cause or increase sexual arousal. [8] It also results in dilation of the blood vessels in the lungs. Pfizer originally discovered the medication in 1989 while looking for a treatment for angina. [50] Overall, this results in a decrease in intracellular calcium and
[11] It was approved for medical use in the United States and in the European Union in 1998. [5][8][11][12] In 2023, it was the 151st most commonly prescribed medication in the United States, with more than 3 million prescriptions. [13][14] It is available as a generic medication. [15][16] In the United Kingdom, it is available as a pharmacy medicine. The primary indication of sildenafil is treatment of erectile dysfunction (inability to sustain a satisfactory erection to complete sexual intercourse).
Its use is now one of the standard treatments for erectile dysfunction, including for males with diabetes mellitus. Tentative evidence suggests that sildenafil may help males who experience antidepressant-induced erectile dysfunction. While sildenafil improves some markers of disease in people with pulmonary arterial hypertension, it does not appear to affect the risk of death or serious side effects. Sildenafil and other PDE5 inhibitors are used off-label to alleviate vasospasm and treat severe ischemia and ulcers in fingers and toes for people with secondary Raynaud's phenomenon;[9][21] these drugs have moderate efficacy for reducing the frequency and duration of vasospastic episodes. [9] As of 2016,[update] their role more generally in Raynaud's was not clear. desensitizing proteins to the effects
of calcium, engendering smooth muscle relaxation.
Sildenafil has shown some potential for improving exercise performance at high altitudes. However, its overall efficacy is not clear. Sildenafil has been studied for high-altitude pulmonary edema (HAPE), but its use is currently not recommended for that indication. In clinical trials, the most common adverse effects of sildenafil use included headache, flushing, indigestion, nasal congestion, and impaired vision, including photophobia and blurred vision. [4] Some sildenafil users have complained of seeing everything tinted blue (cyanopsia).
[24] This cyanopsia can be explained because sildenafil, while selective for PDE5, does have some affinity for PDE6, which is the phosphodiesterase found in the retina. Patients thus taking the drug may experience colorvision abnormalities. Some complained of blurriness and loss of peripheral vision. In July 2005, the US Food and Drug Administration (FDA) updated labeling for tadalafil (Cialis), vardenafil (Levitra), and sildenafil (Viagra) to reflect a small number of post-marketing reports of sudden vision loss, while acknowledging that "...it is not possible to determine whether these oral medicines for erectile dysfunction were the cause of the loss of eyesight or whether the problem is related to other factors such as high blood pressure or diabetes, or to a combination of these problems. "[25] A careful review of pooled data from clinical trials containing well documented information about the dose and duration of exposure to the drug for a large number of patients, yields no evidence for an increased risk of non-arteritic anterior ischemic optic neuropathy or other adverse ocular events associated with PDE5 inhibitor use. The molecular structure of sildenafil is similar to
Rare but serious adverse effects found through postmarketing surveillance include prolonged erections, severe low blood pressure, myocardial infarction (heart attack), ventricular arrhythmias, stroke, increased intraocular pressure, and sudden hearing loss. [4] 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. Care should be exercised by people who are also taking protease inhibitors for the treatment of HIV infection. Protease inhibitors inhibit the metabolism of sildenafil, effectively multiplying the plasma levels of sildenafil, increasing the incidence and severity of side effects. Those using protease inhibitors are recommended to priligy and viagra limit their use of sildenafil to no more than one 25 mg dose every 48 hours.
[4] 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. The use of sildenafil and an α1 blocker (typically prescribed for hypertension or for urologic conditions, such as benign prostatic hypertrophy) at the same time may lead to low blood pressure, but this effect does not occur if they are taken at least 4 hours apart. Concomitant use of nitric oxide donors, organic nitrites and nitrates,[30] such as: nitroglycerinisosorbide mononitrateisosorbide dinitratesodium nitroprussidealkyl nitrites (commonly known as "poppers") Concomitant use of soluble guanylyl cyclase stimulators, such as riociguat Sildenafil should not be used if sexual activity is inadvisable due to underlying cardiovascular risk factors. Sildenafil's popularity with young adults has increased over the years. [32] Sildenafil's brand name, Viagra, is widely recognized in popular culture, and the drug's association with treating erectile dysfunction has led to its recreational use. that of cGMP and acts as a competitive binding
agent of PDE5 in the corpus cavernosum, resulting in
Plano, and Diego A. Golombek of Universidad Nacional de Quilmes, Argentina, for their discovery that sildenafil helps treat jet lag recovery in hamsters. Professional athletes have been documented using sildenafil, believing the opening of their blood vessels will enrich their muscles. In turn, they believe it will enhance their performances. Acetildenafil and other synthetic structural analogs of sildenafil which are PDE5 inhibitors have been found as adulterants in a number of "herbal" aphrodisiac products sold over-the-counter.
[41] These analogs have not undergone any of the rigorous testing that drugs like sildenafil have passed, and thus have unknown side-effect profiles. [42] Some attempts have been made to ban these drugs, but progress has been slow so far, as, even in those jurisdictions that have laws targeting designer drugs, the laws are drafted to ban analogs of illegal drugs of abuse, rather than analogs of prescription medicines. However, at least one court case has resulted in a product being taken off the market. The US Food and Drug Administration (FDA) has banned numerous products claiming to be Eurycoma longifolia that, in fact, contain only analogs of sildenafil. [44][45][46] Sellers of such fake herbals typically respond by just changing the names of their products. more cGMP and increased
Sildenafil and/or N-desmethylsildenafil, its major active metabolite, may be quantified in plasma, serum, or whole blood to assess pharmacokinetic status in those receiving the drug therapeutically, to confirm the diagnosis in potential poisoning victims, or to assist in the forensic investigation in a case of fatal overdose. Nitric oxide (NO) in the corpus cavernosum of the penis binds to guanylate cyclase receptors, which results in increased levels of cGMP, leading to smooth muscle relaxation (vasodilation) of the intimal cushions of the helicine arteries. This smooth muscle relaxation leads to vasodilation and increased inflow of blood into the spongy tissue of the penis, causing an erection. [49] Robert F. Furchgott, Ferid Murad, and Louis Ignarro won the Nobel Prize in Physiology or Medicine in 1998 for their independent study of the metabolic pathway of nitric oxide in smooth muscle vasodilation. penile response to sexual stimulation.
| Condition | Warning Level | Reason |
|---|---|---|
| Uncontrolled hypertension | High | Risk of severe hypotension |
| Cardiovascular disease | High | Increased cardiac risk |
| Use of nitrate medications | High | Dangerous drop in blood pressure |
| Retinitis pigmentosa | Moderate | Potential retinal complications |