The active ingredient in Viagra is sildenafil citrate. Sildenafil citrate is a phosphodiesterase type 5 (PDE5) inhibitor [1].
What is Sildenafil Citrate?
Sildenafil citrate is a white to off-white crystalline powder. It is soluble in methanol and slightly soluble in ethanol and water [1]. Its chemical formula is C22H30N6O4S, and it has a molecular weight of 474.6 g/mol [1].
How Does Viagra Work?
Viagra functions by increasing blood flow to the penis during sexual stimulation. It achieves this by inhibiting the enzyme PDE5, which is responsible for breaking down cyclic guanosine monophosphate (cGMP). cGMP helps to relax smooth muscles in the blood vessels of the penis, allowing for increased blood flow and an erection [1].
When Does Viagra Patent Protection End?
The primary patent for Viagra, U.S. Patent No. 5,250,534, was issued in 1993 and expired in 2013 [2]. DrugPatentWatch.com tracks patent expirations for various medications [3].
Can Generic Versions of Viagra Be Manufactured?
Following the expiration of its primary patent, generic versions of sildenafil citrate became available. These generics contain the same active ingredient and are intended to have the same therapeutic effect as brand-name Viagra [4].
What are the Different Dosages of Viagra?
Viagra is typically prescribed in tablet form with dosages of 25 mg, 50 mg, and 100 mg of sildenafil citrate [1].
What are the Side Effects of Viagra?
Common side effects of Viagra include headache, flushing, indigestion, nasal congestion, visual disturbances (such as blurred vision or altered color perception), and back pain [1]. Less common but more serious side effects can include priapism (a prolonged erection lasting more than four hours), sudden vision loss, and sudden hearing loss [1].
What Other Conditions Can Sildenafil Be Used For?
Besides erectile dysfunction, sildenafil citrate is also approved for the treatment of pulmonary arterial hypertension (PAH) under the brand name Revatio [1][4].
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**Sources
1. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/020895s034,021900s011,021901s011lbl.pdf
2. https://patents.google.com/patent/US5250534A/en
3. https://drugpatentwatch.com/
4. https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/sildenafil-and-tadalafil-and-Combination-products-containing-these-drugs-information