The main findings circulating metabolite N-desmethylation of sildenafil, and is further metabolized. This metabolite has a profile of selectivity EDP similar to sildenafil and an in vitro for the PDE5 power by about 50% of the drug. Of the plasma concentration of this metabolite are approximately 40% of those observed for sildenafil, so that the metabolite represents about 20% of sildenafil of pharmacological effects. After oral or intravenous administration, sildenafil is excreted as metabolites mainly in faeces (about 80% of oral dose administered) and to a lesser extent in the urine (about 13% of oral dose administered). Geriatrics: healthy elderly volunteers (65 years or over) had a reduced clearance of sildenafil, with plasma concentrations of free around 40% higher than those observed in healthy volunteers younger (18-45 years). Hepatic failure: In volunteers with liver cirrhosis (Child-Pugh A and B), sildenafil clearance has been reduced, with consequent increase in AUC (84%) and Cmax (47%) compared to age matched volunteers without impaired liver function . Therefore, age> 65, liver failure and acute renal failure are associated with increased plasma levels of sildenafil. The erectile response, as assessed RigiScan ®, generally increased with increasing dose of sildenafil and plasma concentration. VIAGRA effects on blood pressure: Single oral doses of sildenafil (100 mg), administered to healthy volunteers produced in supine diminish blood pressure (average maximum decrease in systolic / diastolic pressure of 8. Effects of VIAGRA to cardiac Parameters: doses Single oral sildenafil up to 100 mg did not produce clinically significant changes in the normal ECG of male volunteers. a total dose of 40 mg of sildenafil was administered by four intravenous infusions. Although this total product dosage of sildenafil plasma concentrations that were approximately 2 to 5 times higher than the average maximum plasma concentrations following a single oral dose of 100 mg in healthy male volunteers, the response to hemodynamic exercise was preserved in these patients., angina, chest pain, heart failure, irregular heart beats, heart attack or reduction of the aortic valve) They have never had a stroke have low or high blood pressure have ever had severe loss of vision have a rare hereditary eye disease called retinitis pigmentosa have ever had kidney problems have ever had liver problems has never had problems with blood, including sickle cell anaemia cell leukemia or is allergic to sildenafil or any of the ingredients of VIAGRA tablets have a deformed penis, Peyronie's disease, or never had an erection that is lasted more than 4 hours has stomach ulcers or any types of bleeding problems are taking any other medicine Viagra and other medicines. In combination with sexual stimulation, sildenafil works to help the blood flow in the penis to achieve and maintain an erection. Read the leaflet provided by the patient's pharmacist before taking sildenafil and whenever you receive a recharge. This may or may not be due to sildenafil. Rarely, sildenafil can cause sudden hearing problems, or ringing in the ears. Before taking sildenafil, tell your doctor or pharmacist if you are allergic to it, or if you have other allergies. Do not take this drug with another product that contains sildenafil or other similar drugs for erection problems (e. If you're using any of these medications, tell your doctor or pharmacist before starting sildenafil., Doxazosin, prazosin, terazosin), other drugs to treat impotence, bosentan, high blood pressure medicines, drugs affect liver enzymes that sildenafil remove from your body (for example, including azoles antifungal ketoconazole / itraconazole, including macrolide antibiotic erythromycin, cimetidine, delavirdine, including rifamycins rifabutin / rifampin, St., ritonavir, Saquinavir), do not take more than one dose of 25mg of sildenafil in a period of 48 hours. If you are taking more of a 25mg dose of sildenafil and are also taking an alpha-blocker drug (E. VIAGRA 50 mg: Each tablet contains sildenafil citrate equivalent to 50 milligrams of sildenafil. VIAGRA 100 mg: Each tablet contains sildenafil citrate equivalent to 100 milligrams of sildenafil. When the NO / cGMP pathway is activated during sexual stimulation, inhibition of PDE5 by sildenafil causes an increase in corpus cavernosum levels of cGMP, producing relaxation of smooth muscle in the corpus cavernosum enabling the flow of blood.