Common Dosages of Sildenafil Citrate

[97] Health care providers may prescribe generic sildenafil for erectile dysfunction.

• Sildenafil citrate is manufactured by several pharmaceutical companies.
• Its chemical formula is C22H30N6O4S.
• It has a half-life of approximately 4 hours in the body.
• The drug enhances nitric oxide activity in the corpus cavernosum.
• It’s important to follow prescribed dosing to avoid adverse effects.
• It is classified as a phosphodiesterase type 5 inhibitor.
• Sildenafil was initially researched for angina before ED use.

[98] For a time, the generic was not available in the same dosages as branded Viagra, so using dosages typically required for treating ED required patients to take multiple pills. In 1994, Pfizer filed a patent covering the use of sildenafil to treat erectile dysfunction. [99] This would be marketed as Viagra.

Property	Description	Value	Units
Molecular Weight	The mass of one mole of sildenafil citrate	474.58	g/mol
Chemical Formula	Molecular composition	C22H30N6O4S
Solubility	Water solubility	Slightly soluble	at 25°C
pH of Solution	Typical pH when dissolved in water	3.8 - 4.2
Melting Point	The temperature at which it melts	196 - 198	°C

This patent was published in 2002 and expired in 2019. Teva sued to have the latter patent invalidated, but Pfizer prevailed in an August 2011 federal district court case. [100] An agreement with Pfizer allowed Teva to begin to provide the generic drug in December 2017.

Brand Name	Manufacturer	Formulation Type	Typical Dosage	Notes
Viagra	Pfizer	Tablet	25, 50, 100 mg	Most well-known brand
Revatio	Pfizer	Tablet	20 mg	For pulmonary hypertension
Sildenafil Citrate	Various generic manufacturers	Tablet	25, 50, 100 mg	Generic versions available
Kamagra	Ajanta Pharma	Oral Gel	100 mg	Used off-label in some countries

In the United States, Pfizer received two patents for sildenafil: one for its indication to treat cardiovascular disease (marketed as Revatio) and another for its indication to treat erectile dysfunction (marketed as Viagra).

• Contraindications include use with nitrates and recent heart attack.
• Patients with contraindications should avoid sildenafil entirely.
• Visual disturbances including blue-tinted vision may occur.
• Use caution in patients with liver or kidney impairment.
• Sildenafil can interact with certain antibiotics and antifungals.
• Always inform your doctor about other medications you're taking.
• It does not protect against sexually transmitted infections.

The substance is the same under both brand names.

At a glance

[60][61] The drug was patented in 1996, approved for use in erectile dysfunction by the FDA on 27 March 1998, becoming the first oral treatment approved to treat erectile dysfunction in the United States, and offered for sale in the United States later that year. [62] It soon became a great success: annual sales of Viagra peaked in 2008 at US$1.934 billion. In the US, even though sildenafil is available only by prescription from a doctor, it was advertised directly to consumers on TV (famously being endorsed by former United States Senator Bob Dole and football star Pelé). Numerous sites on the Internet offer Viagra for sale after an "online consultation", often a simple web questionnaire. Viagra and other products for sexual dysfunction, termed sexuopharmaceuticals, proliferated new types of specialised marketing for such products.

What is sildenafil, and what is it used for?

[66] Viagra and similar prescription pharmaceuticals were promoted by images in media to the extent of becoming a cultural icon, at the time a relatively new phenomenon known to be permitted only in the United States and New Zealand and which is believed to have significantly contributed to norms regarding male sexuality. [67] One author notes that although the effect of Viagra is only limited to penile blood vessels, advertisements routinely use imagery of couples hugging, smiling and dancing, with the author claiming that pharmaceutical companies were deceptive in the use of such advertisements. In 2000, Viagra sales accounted for 92% of the global market for prescribed erectile dysfunction pills. [69] By 2007, Viagra's global share had plunged to about 50%[70] due to several factors, including the entry of Cialis and Levitra, along with several counterfeits and clones, and reports of vision loss in people taking PDE5 inhibitors. [71][72] In 2008, the FDA forced Pfizer to remove Viva Cruiser, an advergame for Viagra, from appearing on Forbes, after the game failed to disclose risk information about the drug.

Most Recent Events

In February 2007, it was announced that Boots, the UK pharmacy chain, would try over-the-counter sales of Viagra in stores in Manchester, England. Males between the ages of 30 and 65 would be eligible to buy four tablets after a consultation with a pharmacist. [75] In 2017, the Medicines and Healthcare products Regulatory Agency (MHRA) enacted legislation that expanded this nationwide,[76] allowing a particular branded formulation of Sildenafil, Viagra Connect (50 mg), to be sold over the counter and without a prescription throughout the UK from early 2018. While the sale remains subject to a consultation with a pharmacist, the other restrictions from the trial have been removed, allowing customers over the age of 18 to purchase an unlimited number of pills. In May 2013, Pfizer, which manufactures Viagra, told the Associated Press they will begin selling the drug directly to people on its website. Sildenafil is available as a generic drug in the United States, labeled for pulmonary arterial hypertension,[98] and to treat erectile dysfunction, as the patent expired in April 2020.

Product	Dosage	Quantity + Bonus	Price
Viagra Generic	50mg	360 + 10 Pills	225.33€ 214.60€	Buy
Viagra Generic	100mg	90 + 6 Pills	129.02€ 122.88€	Buy
Viagra Generic	100mg	120 + 6 Pills	149.50€ 142.38€	Buy
Viagra Generic	150mg	270 + 10 Pills	326.61€ 311.06€	Buy
Viagra Generic	50mg	30 + 4 Pills	54.26€ 51.68€	Buy
Viagra Generic	100mg	360 + 10 Pills	330.21€ 314.49€	Buy
Viagra Generic	200mg	90 + 6 Pills	170.79€ 162.66€	Buy
Viagra Generic	50mg	120 + 6 Pills	129.64€ 123.47€	Buy
Kamagra	100mg	360 + 6 Pills	839.95€ 799.95€	Buy
Viagra Generic	50mg	60 + 4 Pills	83.93€ 79.93€	Buy
Kamagra Soft Tabs	100mg	272 + 12 Pills	593.42€ 565.16€	Buy
Viagra Generic	200mg	60 + 4 Pills	125.19€ 119.23€	Buy
Viagra Generic	50mg	20 Pills	40.52€ 38.59€	Buy
Viagra Generic	150mg	360 + 10 Pills	423.48€ 403.31€	Buy
Kamagra Soft Tabs	100mg	120 + 6 Pills	311.78€ 296.93€	Buy
Viagra Generic	150mg	30 + 2 Pills	72.32€ 68.88€	Buy
Viagra Generic	150mg	20 Pills	55.02€ 52.40€	Buy

In the US, Revatio and Viagra are marketed by Viatris after Upjohn was spun off from Pfizer.

Before taking this medicine

Pfizer's patents on Viagra expired outside the US in 2012; in the US they were set to expire, but Pfizer settled litigation with each of Mylan and Teva which agreed that both companies could introduce generics in the US in December 2017. [79][80] In December 2017, Pfizer released its buy sildenafil online uk own generic version of Viagra. As of 2018[update], the US Food and Drug Administration has approved fifteen drug manufacturers to market generic sildenafil in the United States. Seven of these companies are based in India. The patent for Pfizer's Viagra sildenafil to treat erectile dysfunction expired in April 2020.

Erectile dysfunction

In 2026 a chocolate syrup called Boner Bears from Lockout Supplements was recalled through the FDA because of it containing Sildenafil as an undisclosed ingredient. Counterfeit Viagra, despite generally being cheaper,[88] can contain harmful substances or substances that affect how Viagra works, such as blue printer ink, amphetamines, metronidazole, boric acid, and rat poison. Viagra is one of the world's most counterfeited medicines. [90][91] According to a 2012 Pfizer study, around 80% of sites claiming to sell Viagra were selling counterfeits. An October 2023 release stated that erectile dysfunction medicines were the most seized drugs by the Interpol[92] accounting for 22% of seizures. In Canada, Pfizer's patent 2,324,324 for Revatio (sildenafil used to treat pulmonary hypertension) was found invalid by the Federal Court in June 2010, on an application by Ratiopharm Inc.[106][107] On 8 November 2012, the Supreme Court of Canada ruled that Pfizer's patent 2,163,446 on Viagra was invalid from the beginning because the company did not provide full disclosure in its application.

Related/similar drugs

In 1992, Pfizer filed a patent covering the substance sildenafil and its use to treat cardiovascular diseases. [96] This would be marketed as Revatio. The patent was published in 1993 and expired in 2012. The patent on Revatio (indicated for pulmonary arterial hypertension rather than erectile dysfunction) expired in late 2012. Generic versions of this low-dose form of sildenafil have been available in the US from a number of manufacturers, including Greenstone, Mylan, and Watson, since early 2013. The decision, Teva Canada Ltd.

Condition	Description	Recommended Dosage	Notes
Erectile Dysfunction (ED)	Difficulty achieving or maintaining an erection	50 mg before activity	Can be adjusted based on response
Pulmonary Arterial Hypertension	High blood pressure in lungs	20 mg three times daily	Prescribed under medical supervision
Off-label uses	Other potential uses	Varies	Use under healthcare provider guidance

v. Pfizer Canada Inc., pointed to section 27(3)(b) of The Patent Act which requires that disclosure must include sufficient information "to enable any person skilled in the art or science to which it pertains" to produce it. It added further: "As a matter of policy and sound statutory interpretation, patentees cannot be allowed to 'game' the system in this way. This, in my view, is the key issue in this appeal.

• Some users report headaches and dizziness after taking sildenafil.
• A common side effect is facial flushing and nasal congestion.
• Rare side effects include sudden hearing loss or vision loss.
• Priapism requires urgent medical attention to prevent tissue damage.
• Sudden vision loss should be immediately evaluated by a doctor.
• Allergic reactions such as rash, hives, or swelling are possible.
• Discontinue use and seek medical help if serious side effects occur.

Teva Canada launched Novo-Sildenafil, a generic version of Viagra, on the day the Supreme Court of Canada released its decision. [109][110][111] To remain competitive, Pfizer then reduced the price of Viagra in Canada. [112] However, on 9 November 2012, Pfizer filed a motion for a re-hearing of the appeal in the Supreme Court of Canada,[113] on the grounds that the court accidentally exceeded its jurisdiction by voiding the patent. [114] Finally, on 22 April 2013, the Supreme Court of Canada invalidated Pfizer's patent altogether.

• Sildenafil citrate may cause a drop in blood pressure.
• Do not consume large quantities of grapefruit juice while on sildenafil.
• Pregnant or breastfeeding women should not use sildenafil without guidance.
• The drug does not improve libido, only facilitates blood flow.
• It is not intended for recreational use or enhancement.
• Psychological factors can also affect the efficacy of sildenafil.
• Regular medical check-ups are recommended for long-term users.

Manufacture and sale of sildenafil citrate drugs is common in China, where Pfizer's patent claim is not widely enforced.

Chemical synthesis

[49][51] Without sexual stimulation, and therefore lack of activation of the NO/cGMP system, sildenafil should not cause an erection. Other drugs that operate by the same mechanism include tadalafil (Cialis) and vardenafil (Levitra). Sildenafil is broken down in the liver by hepatic metabolism using cytochrome p450 enzymes, mainly CYP450 3A4 (major route), but also by CYP2C9 (minor route) hepatic isoenzymes. The major product of metabolisation by these enzymes is N-desmethylated sildenafil, which is metabolised further. This metabolite also has an affinity for the PDE receptors, about 40% of that of sildenafil.

Lactation Precautions

Thus, the metabolite is responsible for about 20% of sildenafil's action. Sildenafil is excreted as metabolites predominantly in the feces (about 80% of administered oral dose) and to a lesser extent in the urine (around 13% of the administered oral dose). If taken with a high-fat meal, absorption is reduced; the time taken to reach the maximum plasma concentration increases by around one hour, and the maximum concentration itself is decreased by nearly one-third. When taken orally, sildenafil for erectile dysfunction results in an average time to onset of erections of 27 minutes (ranging from 12 to 70 minutes). Sublingual use of sildenafil for erectile dysfunction results in an average onset of action of 15 minutes and lasting for an average of 40 minutes.

Dosage Modifications

The preparation steps for synthesis of sildenafil are:[54] Methylation of 3-propylpyrazole-5-carboxylic acid ethyl ester with hot dimethyl sulfate Hydrolysis with aqueous sodium hydroxide (NaOH) to free acid Carboxamide formation with refluxing thionyl chloride/NH4OH Reduction of nitro group to amino group Sildenafil (compound UK-92,480) was synthesized by a group of pharmaceutical chemists led by Simon Campbell[55] working at Pfizer's Sandwich, Kent, research facility in England. It was initially studied for use in hypertension (high blood pressure) and angina pectoris (a symptom of ischaemic heart disease). [56] The first clinical trials were conducted in Morriston Hospital in Swansea. [57] Phase I clinical trials under the direction of Ian Osterloh suggested the drug had little effect on angina, but it could induce marked penile erections. [58][59] Pfizer therefore decided to market it for erectile dysfunction, rather than for angina; this decision became an often-cited example of drug repositioning. Egypt approved Viagra for sale in 2002, but soon afterwards allowed local companies to produce generic versions of the drug, citing the interests of poor people who would not be able to afford Pfizer's price.