Patient Counseling Points for Sildenafil Citrate Therapy

Protease inhibitors inhibit the metabolism of sildenafil, effectively multiplying the plasma levels of sildenafil, increasing the incidence and severity of side effects.

Related/similar drugs

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. Those using protease inhibitors are recommended to limit their use of sildenafil to no more than one 25 mg dose every 48 hours.

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[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.

Utilisation dans l'hypertension artérielle pulmonaire

However, the ratio of the metabolite to sildenafil is higher in patients with pulmonary arterial hypertension (PAH). The metabolite is further metabolized to inactive compounds. Sildenafil is excreted as metabolites primarily in the feces (approximately 80% of administered oral dose) and to a lesser extent in the urine (approximately 13% of the administered oral dose). Both sildenafil and its active metabolite have terminal half-lives of about 4 hours. Sildenafil concentrations at 24 hours post a single 100 mg oral dose average 2 ng/mL (compared to peak plasma concentrations of approximately 440 ng/mL).

What is sildenafil used for?

While similar pharmacokinetic parameters were observed in healthy volunteers and patients with erectile dysfunction, the average steady-state concentrations were 20% to 50% higher and Cmin levels doubled in patients with PAH compared to healthy volunteers. Affected cytochrome P450 isoenzymes: CYP3A4 and CYP2C9Sildenafil is metabolized principally by the hepatic cytochrome P450 (CYP) 3A4; CYP2C9 is also involved to a lesser degree. Dosage reductions are recommended for patients receiving potent cytochrome CYP3A4 inhibitors. Sildenafil is rapidly absorbed after oral administration, with a mean absolute bioavailability of about 41% (25% to 63%). Its pharmacokinetics are dose-proportional over the recommended dose range.

Clinical monitoring

Maximum observed plasma concentrations are reached within 30 to 120 minutes (median 60 minutes) of oral dosing in the fasted state. Oral Suspension (Liqrev):When sildenafil is taken with a high fat meal, the rate of absorption is reduced, with a mean delay in Tmax of 60 minutes and a mean reduction in Cmax of 53%; the extent of absorption (AUC) is increased by 11%.Oral tablets and oral powder for suspension (Revatio, Viagra):When sildenafil is taken with a high fat meal, the rate of absorption is reduced, with a mean delay in Tmax of 60 minutes and a mean reduction in Cmax of 29%. A 10 mg IV dose is predicted to provide a pharmacological effect of sildenafil and its N-desmethyl metabolite equivalent to that of a 20 mg PO dose. Limited data do not report a clear association with the use of sildenafil and major birth defects, miscarriage, or adverse maternal or fetal outcomes when sildenafil is used during pregnancy. No evidence of teratogenicity or embryofetal toxicity was observed in animal reproduction studies using sildenafil at doses 32- and 65-times the recommended human dose. 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.

Country	Legal Status	Prescription Requirement	Notes
USA	Prescription-only medication	Yes	FDA approved
UK	Prescription-only	Yes	MHRA regulated
India	Over-the-counter and prescription	Both are possible	Varies by state
Australia	Prescription only	Yes	TGA regulated

[33] The reasons behind such use include the belief that the drug increases libido, improves sexual performance,[33] or permanently increases penis size.

• The discovery of sildenafil began with research on heart drugs.
• It was found to cause vasodilation as a side effect.
• Pfizer refined the drug for erectile dysfunction.
• It became a blockbuster drug upon FDA approval.
• Sildenafil has helped millions worldwide.
• It has changed perceptions about male sexual health.
• Ongoing research explores new formulations.
• Awareness campaigns promote safe usage.

[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.

Drug Class	Interaction Effect	Clinical Significance
Nitrates	Potentiates hypotension	Absolute contraindication
Alpha-blockers	Increased hypotensive effect	Use with caution
CYP3A4 inhibitors	Increased sildenafil levels	Dose adjustment needed
Protease inhibitors	Elevates sildenafil exposure	Increased side effects

In one study, a 25 mg dose was shown to cause no significant change in erectile quality, but did reduce the postejaculatory refractory time.

Frequently asked questions

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. 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. [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.

4. Bottom Line

[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. [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.

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[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 Tablets for ED

Sildenafil and other PDE5 inhibitors sildenafil for women 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. 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. [36] Sildenafil is sometimes used to counteract the effects of other substances, often illicit.

Non-medical use

There are risks to the mother and fetus from untreated pulmonary arterial hypertension. Limited clinical data preclude a clear determination of the risk of sildenafil to an infant during breast-feeding. Data from a case report describe the presence of sildenafil and its active metabolite in human milk. There is insufficient information on the effects of sildenafil on the breast-fed infant and no information on the effects of sildenafil on milk production. Sildenafil, sold under the brand name Viagra among others, is a medication used to treat erectile dysfunction and pulmonary arterial hypertension.

Drug Interactions

[4][8] It is also sometimes used off-label for the treatment of certain symptoms in secondary Raynaud's phenomenon. [9] It is unclear if it is effective for treating sexual dysfunction in females. [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.

Interactions that increase your risk for side effects

[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 sildenafil oral strips increase sexual arousal. [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".

• Sildenafil can cause sudden vision loss (rare side effect).
• Men with a history of retina problems should use caution.
• It may cause a drop in blood pressure, leading to dizziness.
• Patients should report any persistent erection lasting over 4 hours.
• It is crucial to have proper medical evaluation before use.
• Not suitable for individuals with severe liver or kidney conditions.
• The medication is also investigated for breast cancer treatment.
• Proper hydration can help minimize some side effects.