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Viagra | Revatio | Sildenafil Citrate is used to treat male sexual function problems; impotence or erectile dysfunction (ED).

Therapeutic Class:

Drugs for Erectile Dysfunction

Pharmacology:

Sildenafil Citrate belongs to a group of medicines called phosphodiesterase type-5 (PDE-5) inhibitors. It works by helping to relax the blood vessels of penis, allowing blood to flow into penis. The physiologic mechanism of erection of the penis involves release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation.

NO then activates the enzyme guanylate cyclase, which results in increased levels of cyclic guanosine monophosphate (cGMP), producing smooth muscle relaxation in the corpus cavernosum and allowing inflow of blood.

When sexual stimulation causes local release of NO, inhibition of PDE-5 by sildenafil causes increased levels of cGMP in the corpus cavernosum, resulting in smooth muscle relaxation and inflow of blood to the corpus cavernosum. Sildenafil at recommended doses has no effect in the absence of sexual stimulation.

Dosage:

The usual starting dose of Sildenafil is 50 mg once daily. It should be taken before 30-40 minutes of intercourse. Depending on effectiveness and tolerance; the dose may be increased to a maximum recommended dose of 100 mg or decreased to 25 mg. The maximum dosing frequency is once per day.

Some factors are associated with increased plasma levels of Viagra: age>65, hepatic impairment, severe renal impairment and concomitant use of ketoconazole, itraconazole, erythromycin. Since higher plasma levels may increase both the efficacy and incidence of adverse events.

Administration:

Sildenafil may take longer time to work if you take it with a heavy meal.

Interaction:

Inhibitors of CYP3A4 such as cimetidine and erythromycin are likely to reduce Viagra clearance. CYP3A4 inducers such as rifampicin may decrease the plasma concentrations of sildenafil. Symptomatic hypotension when used with α-blockers. Plasma concentrations are increased by ritonavir.

Contraindications:

Viagra was shown to potentiate the hypotensive effects of nitrates and its administration to patients who are using organic nitrates, either regularly and or intermittently, in any form is therefore contraindicated.

Side Effects:

Like all medicines, Sildenafil can cause side effects although not everybody gets them.The side effects reported in association with the use of Viagra are usually mild to moderate and of a short duration. All medicines including Sildenafil can cause allergic reactions.

Contact with doctors immediately if experiences any of the following symptoms after taking Viagra: sudden wheeziness, difficulty in breathing or dizziness, swelling of the eyelids, face, lips or throat.

Common side effect includes headache, facial flushing, indigestion, effects on vision, light sensitivity, blurred vision or reduced, stuffy nose and dizziness. Uncommon side effect includes vomiting, skin rash, bleeding at the back of the eye, red eyes, eye pain, double vision, abnormal sensation.

Pregnancy & Lactation:

Viagra is not indicated for use in newborns, children & women.

Precautions:

Warnings: In patients with preexisting cardiovascular disease, there is a potential risk in sexual activity. Sildenafil should not be generally used in men for whom sexual activity is inadvisable because of their underlying cardiovascular status.

Sildenafil has systemic vasodilatory properties (mean maximum decrease of 8.4/5.5 mmHg). Patients with left ventricular outflow obstruction (e.g. aortic stenosis, idiopathic hypertrophic subaortic stenosis) and those with severely impaired autonomic control of blood can be particularly sensitive.

There is no controlled clinical data on the safety or efficacy of Viagra in Patients who have suffered from a myocardial infarction, stroke, or life-threatening arrhythmia within the last 6 months. Caution should be taken in patients with resting hypotension.

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 this situation, patient should seek immediate medical assistance.

Overdose Effects:

In studies with healthy volunteers of single doses up to 800 mg, adverse events were similar to those seen at lower doses, but incidence rates and severities were increased. In cases of overdose, standard supportive measures should be adopted as required.

Renal dialysis is not expected to accelerate clearance as Viagra is highly bound to plasma proteins and it is not eliminated in the urine.

Storage Conditions:

Store below 30° C. Protect from light and moisture. Keep out of reach of children.