The way Fildena 150 mg works is by inhibiting the PDE5 enzyme, which controls blood flow via the penis. By inhibiting PDE5, cyclic guanosine monophosphate is produced, which raises the degree of relaxation of the smooth muscles in that penile region. This facilitates relaxed blood flow, which supports the maintenance of an erection following sexual stimulation. Can be taken as prescribed by your doctor, either with or without food. You should take the medication 30 to 60 minutes before having intercourse. You may take it up to four hours prior to sexual activity, though. This medicine only works to maintain an erection while you are in a sexually stimulating environment.