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What Is Viagra and How Does It Work?

All three of the erectile dysfunction drugs (Viagra, Levitra and Cialis) are similar in action. Viagra blocks an enzyme that causes an erection to go flaccid. Although Viagra, Levitra and Cialis are similar in action, their dose, onset of action time and duration of action differ.

Viagra (Sildenafil) is a member of a family of drugs called PDE5 Inhibitors. Viagra was the first PDE5 inhibitor on the market. FDA was approved Viagra on March 27, 1998. The team of scientists who discovered Viagra won the Nobel Prize.

The BIG Discovery: cyclic guanosine monophosphate (cGMP)

Some very smart scientists discovered that cyclic guanosine monophosphate (cGMP) was the key to sustaining an erection.

They discovered that when a man gets sexually stimulated, a chain reaction occurs in the tissue of the penis that results in elevated levels of a substance called cyclic guanosine monophosphate (cGMP).

As long as there are sufficient levels of cGMP, the penis can remain erect. The more cGMP, the more robust and durable the erection.

If you inhibit the degradation (breakdown) of cGMP it stays around in the penis longer, producing a more durable erection.

Another way you can think of Viagra (and all other similar medicines) is that it preserves the elevated levels of cGMP that are created when a man is sexually stimulated for a stronger, more lasting erection.

That's how Viagra works - Viagra blocks the enzyme phosphodiesterase-5 (PDE5) which is responsible for the neutralization of cGMP. Viagra (Sildenafil) is a highly selective inhibitor of PDE5. (PDE5 is not the only phosphodiesterase involved in the erectile physiology but it appears to be the most important one).

The nice thing about PDE5 blockers is that they shouldn't cause erections at inappropriate times because they only block degradation of cGMP produced in reaction to sexual stimulation, such as thinking about something sexy.

If you are not being sexually stimulated, there is no cGMP to protect, so the drug remains in the background.

Non-Sexual Uses For Viagra:

The active ingredient in Viagra (silendafil) is useful in treating a rare, potentially deadly condition known as pulmonary hypertension.

In this use, Viagra's Phosphodiesterase 5 blocking activity is thought to be beneficial in relaxing the smooth muscle tissue found in the lungs by increasing the levels of cyclic guanasine monophosphate (cGMP).

Viagra Absorption, Bioavailability

Viagra is rapidly absorbed. Maximum observed plasma concentrations of Viagra are reached within 30 to 120 minutes (median 60 minutes) of oral dosing in the fasted state. Viagra is about 40% biovailable. Viagra is highly protein bound (96%). When Viagra is taken with a high fat meal, the rate of absorption is reduced.

Metabolism, Half Life, and Excretion of Viagra

Viagra is mostly metabolized in the liver by an enzyme known as CYP3A4 and to a lesser extent CYPC229. Viagra breakdown products are excreted in the feces (80%) and in the urine (approximately 13%). Viagra's mean half life is about 4 hours.

If you are going to take any of the PDE5 inhibitors such as Viagra, it is very important that your doctor be aware if you have a liver condition (such as cirrhosis) or kidney condition ( such as if you are on dialysis) because you may need a special viagra dosage adjustment.

Likewise, if you try to obtain Viagra on the internet, please make sure that the person authorizing your viagra prescription knows the true status of your liver function and your kidney function.

Viagra Dose:

For most patients, the recommended dose of Viagra is 50mg taken about 1 hour prior to anticipated sexual activity. However, the Viagra label states that it can be taken anywhere from 1/2 hour to 4 hours prior to sexual activity.

The dose of Viagra may be increased to 100mg or decreased to 25 mg depending on efficacy and side effects. Sometimes people buy the 100mg tablets and break them in half to save money.