The main ingredient in Fildena 25 medicine is sildenafil. Sildenafil affects the response to sexual arousal. It works by using nitric oxide to increase muscle relaxation, and the chemical sildenafil may be used for other purposes not listed above. It is taken orally with a glass of water about 5-1 hours before sexual activity. Fildena should not be taken more than once a day. A high-fat diet may delay the effect of this drug. Try not to eat grapefruit or drink grapefruit juice while you are being treated with sildenafil.