Description

INDICATION

VIAGRA is a phosphodiesterase-5 (PDE5) inhibitor indicated for the treatment of erectile dysfunction (ED)

DOSAGE

For most patients, the recommended dose is 50 mg taken, as needed, approximately 1 hour before sexual activity. However, VIAGRA may be taken anywhere from 30 minutes to 4 hours before sexual activity.

The maximum recommended dosing frequency is once per day.

Based on effectiveness and toleration, the dose may be increased to a maximum recommended dose of 100 mg or decreased to 25 mg.

Mechanism of Action:

The active ingredient of the Viagra is Sildenafil. Sildenafil plays an important role in the production of Cyclic GMP. Sildenafil protects cyclic guanosine monophosphate (c  GMP) from degradation by c GMP – specific phosphodiesterase type 5 (PDE5) in the corpus cavernosum. Nitric oxide in the corpus cavernosum of the genital bind to guanylate cyclase receptors, which results in an increased level of c GMP, leading to smooth muscle relaxation (vasodilation ) of the intimal cushions of the helicine arteries. This smooth muscle relaxation leads to vasodilation and increases the inflow of blood into the spongy tissue, so the erection occurs.

The molecular mechanism of smooth muscle relaxation involves the enzyme c  GPM-dependent protein kinase, also known as PKG. the kinase is activated by c GMP and its phosphorylates multiple targets in the smooth muscle cells, namely myosin light phosphatase, RhoA, IP3 receptor, phospholipase C, and others. This results in a decrease in the intracellular calcium and desensitizing proteins to affect the calcium, engendering smooth muscle relaxation.

Sildenafil is a potent and selective inhibitor of c GMP- specific phosphodiesterase type 5 (PDE5), which I responsible for the degradation of c GMP in the corpus cavernosum. The molecular structure of sildenafil is similar to that of c GMP and acts as a competitive binding agent of PDE5 in the corpus cavernosum, resulting in more c GMP and better erections. Without sexual stimulation,  and therefore lack of activation of the NO/c GMO system, the sildenafil should not cause an erection.

Sildenafil is broken down in the liver by hepatic metabolism using cytochrome p450 enzymes, mainly CYP450 3A4 (major route), but also by CYP2C9 (minor route) hepatic isoenzymes.
Prolonged Erection and Priapism

Prolonged erection greater than 4 hours and priapism (painful erections greater than 6 hours in duration) have been reported infrequently since market approval of VIAGRA. In the event of an erection that persists longer than 4 hours, the patient should seek immediate medical assistance. If priapism is not treated immediately, penile tissue damage and permanent loss of potency could result.

VIAGRA should be used with caution in patients with anatomical deformation of the penis (such as angulation, cavernosal fibrosis or Peyronie’s disease), or in patients who have conditions which may predispose them to priapism (such as sickle cell anemia, multiple myeloma, or leukemia). However, there are no controlled clinical data on the safety or efficacy of VIAGRA in patients with sickle cell or related anemias.

Viagra side effects

Get emergency medical help if you have signs of an allergic reaction to Viagra: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Stop taking Viagra and get emergency medical help if you have:

•   heart attack symptoms–chest pain or pressure, pain spreading to your jaw or shoulder, nausea, sweating;
•   vision changes or sudden vision loss; or
•   erection is painful or lasts longer than 4 hours (prolonged erection can damage the penis).

Call your doctor at once if you have:

•   ringing in your ears, or sudden hearing loss;
•   irregular heartbeat;
•   swelling in your hands, ankles, or feet;
•   shortness of breath;
•   seizure (convulsions); or
•   a light-headed feeling, like you might pass out.

Common Viagra side effects may include:

•   flushing (warmth, redness, or tingly feeling);
•   headache, dizziness;
•   abnormal vision (blurred vision, changes in color vision)
•   stuffy nose;
•   muscle pain, back pain; or
•   upset stomach