Pharmacokinetics and toxicokinetics were adequately studied and toxicity was tested appropriately.Sildenafil citrate is designated chemically as 1-[[3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1H­pyrazolo[4,3-d]pyrimidin-5-yl)-4-ethoxyphenyl]sulfonyl]-4-methylpiperazine citrate and has the following structural formula: C N NHO2S N N CH3 H3CH2O O N N CH3 CH2CH2CH3 HOOC OH CO2H CO2H Sildenafil citrate is a white to off-white crystalline powder with a solubility of 3. natural viagra.