The substance is the same under both trade names.In 1992, Pfizer filed a patent covering the substance sildenafil and its use to treat cardiovascular diseases. 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 U.S. from a number of manufacturers, including Greenstone, Mylan, and Watson, since early 2013. Health care providers may prescribe generic sildenafil for erectile dysfunction. However, the generic is not available in the same dosages as branded Viagra, so using dosages typically required for treating ED requires patients to take multiple pills.In 1994, Pfizer filed a patent covering the use of sildenafil to treat erectile dysfunction. This would be marketed as Viagra. This patent was published in 2002 and will expire in 2019. Teva sued to have the latter patent invalidated, but Pfizer prevailed in an August 2011 federal district court case. An agreement with Pfizer allowed Teva to begin to provide the generic drug in December 2017. References
External links

"Sildenafil". Drug Information Portal. U.S. National Library of Medicine. "Sildenafil citrate". Drug Information Portal. U.S. National Library of Medicine. Viagra at The Periodic Table of Videos (University of Nottingham)
Therefore, he named the new organism Bacillus pseudomallei. He did no further work on the organism. Arthur Conan Doyle may have read Whitmores report before writing a short story that involved the fictitious tropical disease "Tapanuli fever" in a Sherlock Holmes story titled "The Adventure of the Dying Detective" published in 1913. In the same year, melioidosis outbreak occurred inside the Institute for Medical Research (IMR), Kuala Lumpur, Malaya after its laboratory animals such as guinea pigs and rabbits were infected. William Fletcher and Ambrose Thomas Stanton, doctors who worked at the IMR, were the next ones to study the organism. They were unable identify the organism that caused the outbreak. It was only in 1917, when Fletcher isolated an organism similar to Whitmores bacillus from a Tamil rubber estate worker, the presence of the new species of bacteria was confirmed. The term "melioidosis" was first coined in 1921. The name melioidosis is derived from the Greek melis (μηλις) meaning "a distemper of asses" with the suffixes -oid meaning  "similar to" and -osis meaning "a condition", that is, a condition similar to glanders. B pseudomallei is similar in clinical presentation and genome make-up with B. mallei but is distinguished from it due to epidemiological and zoonotic characteristics.The first human case of melioidosis in South Asia was reported in Sri Lanka in 1927. In 1932, Thomas and Fletcher collected 83 cases of melioidosis from literature. In this case series, there were only two survivals. Since then, more case series of melioidosis were reported.