Since Fildena 25 is a phosphodiesterase Type 5 inhibitor, it works by boosting local blood flow. Male penile tissue naturally contains an enzyme called PDE5. Before taking the medication with water, avoid crushing or chewing it. Usually provided to men with moderate ED or who wish to reduce the possibility of side effects, this is the lowest dose. Depending on the individual, the effects of Fildena 25 usually persist for four to six hours after the prescription is taken. Although they are uncommon, more severe side effects like visual problems or hearing loss can happen.