Side effects of Viagra buy viagra
In clinical trials, the most common adverse effects of sildenafil use included headache, flushing, dyspepsia, nasal congestion and impaired vision, including photophobia and blurred vision.[34] Some sildenafil users have complained of seeing everything tinted blue (cyanopsia).[35] Some complained of blurriness and loss of peripheral vision. In July 2005, the U.S. Food and Drug Administration found that sildenafil could lead to vision impairment in rare cases[36] and a number of studies have linked sildenafil use with nonarteritic anterior ischemic optic neuropathy.[37][38][39][40][41][42]
Rare but serious adverse effects found through postmarketing surveillance include priapism, severe hypotension, myocardial infarction (heart attack), ventricular arrhythmias, stroke, increased intraocular pressure and sudden hearing loss.[34] As a result of these postmarketing reports, 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.[43]
Interactions
Care should be exercised by patients who are also taking protease inhibitors for the treatment of HIV. Protease inhibitors inhibit the metabolism of sildenafil, effectively multiplying the plasma levels of sildenafil, increasing the incidence and severity of side-effects. It is recommended that patients using protease inhibitors limit their use of sildenafil to no more than one 25 mg dose every 48 hours.[citation needed]
Concomitant use of sildenafil and an alpha blocker may lead to low blood pressure, but this effect does not occur if they are taken at least four hours apart.[44]
Chemical synthesis
The preparation steps for synthesis of Viagra buy viagra(sildenafil citrate) are as follows:[45]
Methylation of 3-propylpyrazole-5-carboxylic acid ethyl ester with hot dimethyl sulfate.
Hydrolysis with aqueous NaOH to free acid.
Nitration with oleum/fuming nitric acid.
Carboxamide formation with refluxing thionyl chloride/NH4OH.
Reduction of nitro group to amino.
Acylation with 2-ethoxybenzoyl chloride.
Cyclization.
Sulfonation to the chlorosulfonyl derivative.
Condensation with 1-methylpiperazine.
Contraindications
Contraindications include:[citation needed]
When taking nitric oxide donors, organic nitrites and nitrates, such as glyceryl trinitrate (nitroglycerin), sodium nitroprusside, amyl nitrite (“poppers”)[33]
In men for whom sexual intercourse is inadvisable due to cardiovascular risk factors
Severe hepatic impairment (decreased liver function)
Severe impairment in renal function
Hypotension (low blood pressure)
Recent stroke or heart attack
Hereditary degenerative retinal disorders (including genetic disorders of retinal phosphodiesterases)
Dosage
Viagra
Viagra pills are blue and diamond-shaped with the words “Pfizer” engraved on one side, and “VGR xx” (where xx stands for “25″, “50″ or “100″, the dose of that pill in milligrams) engraved on the other. The dose of sildenafil for erectile dysfunction is 25 mg to 100 mg taken not more than once per day between 30 minutes and 4 hours prior to sexual intercourse.
The dosage for pulmonary arterial hypertension (Revatio) is one 20 mg tablet three times a day. Revatio pills are white, round, film-coated tablets imprinted with “RVT 20″ embossed on one side.[32]
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