Fildena 150mg tablet lasts for about four hours maximum and two hours minimum. Therefore, the sildenafil agents in the body's bloodstream start to decrease every four hours. Fildena 120mg take about 30 minutes to interact with the human body system and start working. However, the speed of action of Fildena 150mg starts to decrease after two hours. Different brands work differently, that's why Fildena 150mg is effective and its speed of action is fast and effective.