Hello, Viagra tablets contain the active ingredient sildenafil, which is a medicine used in the treatment of erectile dysfunction (impotence). This medicine may cause dizziness and visual disturbances. Viagra tablets should preferably be taken on an empty stomach.Since most of the tablets metabolised in liver and excreted in urine . Normal functioning of theses two organs is very important. Your kindney is compromised, don't take this medicine without physician consultation.