Kamagra or Sildenafil is available as oral tablets at doses of 25, 50, and 100 mg. It should be taken approximately one hour before sexual activity. In some men, the onset of action of the drug may be as early as 11-20 minutes. Sildenafil should be taken on an empty stomach for best results since absorption and effectiveness of sildenafil can be diminished if it is taken shortly after a meal, particularly a meal that is high in fat.