How does Fildena Double 200 work? Phosphodiesterase inhibitors are a group of drugs that are present in the Sildenafil Citrate part of Fildena double 200. When the blood supply from the penis decreases and the blood flow from the veins to the penis increases, males have a penile erection. The prescriptions contain Sildenafil Citrate, a synthetic drug used to treat hypertension, erectile...