by Anthony Roberts - Viagra (Sildenafil citrate) is a drug used to treat erectile dysfunction (impotence) in males and pulmonary arterial hypertension (PAH).

Background

The pharmaceutical company, Pfizer, originally developed Viagra. In 1006, the FDA approved Viagra as the first drug patented for use of erectile dysfunction in the United States.  They are blue, diamond-shaped pills with "Pfizer" marked on one side and "VGR XX." The XX is the dosage, which is either 25,50, or 100 mgs.  Viagra is also sold under the brand name Revatio and generically under various other names.  It is also widely availabe by many research companies and underground labs.

Action

Viagra treats erectile dys function and works by relaxing muscles and increases blood flow to particular areas of the body (in this case, the penis, specifically).  Its effects last up to four hours.  The most common side effects of Viagra are headache, facial flushing, and upset stomach. Rarely, blurred vision, or sensitivity to light may briefly occur.

As well as treating impotence, Sildenafil Citrate can also be effective in treating Pulmonary Arterial Hypertension (PAH).  Similarly to how it acts to relax muscles of the penis, it relaxes arterial walls; therefore, reducing resistance and pressure in the arteries. 

Sildenafil Citrate is solely active in relaxing muscles and increasing blood flow to the heart, lungs and penis due to PDE-5, yet vasodilation is not increased in other parts of the body.

Technical Data

In studies where Viagra was administered to over 3700 patients, 19-87 years old in world wide clinical trials. More than 550 patients received treatment post 1 year.  2.5% of the Viagra subjects and 2.3% of the placebo subjects reported adverse effects, which were all considered mild.  These reported side effects included abnormal or blurred vision and increased sensitivity to light (1).  All other negative reactions reported, including URI, flu symptoms, back pain and arthralgia, occurred at a rate of less than 2% and equally common in the placebo and Viagra administered groups (1).  Effects worsened and were reported more frequently as dosages increased (1). 

Other studies measured duration of sexually stimulated erection using a Rigiscan device.  Duration of rigidity was increased by 60% with Viagra use (2).

In 16 separate 4-24 week trials of men (over 18 years old) who suffered from impotence for longer than 6 months, dosages between 10-200 mgs were administered (3).  Significant improvements in erectile function, including frequency of penetration as well as erection duration post penetration, were reported with Sildenfil treatment compared to the placebo group (4). Erections were improved in 72% of the Viagra group verses 18% of the placebo group (5).  In all cases effects were dependant upon dosage and improvement was the greatest when dosage exceeded 100 mgs (6).  Responses were decreased by 40-60% in patients suffering from diabetes and prostatectomy, respectively (7)(8).  Withdrawal rates were less than 5% related to negative side effects and limited response rates (9).

Sildenafil citrate is the chemical name of active ingredient in Viagra. Viagra is a registered trademark of Pfizer Inc. in the United States and/or other countries.

Viagra Resources

Viagra Prescribing Information

References

1. http://www.rxlist.com/cgi/generic/viagra_ad.htm, 2007, 28, February
2. FDA Centre for Drug Evaluation and Research. Joint clinical review for NDA-20-895. January 1998.
3. Boolell M et al. Sildenafil, a novel effective oral therapy for male erectile dysfunction. Br.J.Urol. 1996; 37: 257-261.
4. Goldstein I et al for the Sildenafil Study Group. Oral sildenafil in the treatment of erectile dysfunction. N.Engl.J.Med 1998; 338: 1397-1404.
5. Rendell MS, Rajfer J, Wicker PA et al. Sildenafil for Treatment of Erectile Dysfunction in Men With Diabetes. A Randomized Controlled Trial. JAMA 1999; 281: 421-426
6. FDA Centre for Drug Evaluation and Research. Joint clinical review for NDA-20-895. January 1998.
7. Rendell MS, Rajfer J, Wicker PA et al. Sildenafil for Treatment of Erectile Dysfunction in Men With Diabetes. A Randomized Controlled Trial. JAMA 1999; 281: 421-426
8. FDA Centre for Drug Evaluation and Research. Joint clinical review for NDA-20-895. January 1998.
9. Morales A et al. Clinical safety of oral sildenafil citrate (Viagra) in the treatment of erectile dysfunction. Int.J.Impot.Res. 1998; 10: 69-74.

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