When looking for medications to treat ED, two of the most popular brand names are Fildena 100 vs Viagra. The active component of the generic form of Viagra is sildenafil citrate. The optimal time to take sildenafil or viagra is 30 to 60 minutes before engaging in sexual activity.  You can take generic sildenafil or Viagra with or without food, however you shouldn't take either one with a high-fat meal since this may reduce the effectiveness of both drugs. In general, Fildena can be taken orally together with a glass of water.