Patients who take Fildena should follow the instructions on the medication label carefully. In rare cases, patients taking the medicine may experience vision loss in one or both eyes. The patient should be advised to take the medication after drinking alcohol to prevent unwanted side effects. The patient should not take two doses at once. If the condition worsens, the doctor will suggest another dose. It is important to follow the dosage instructions strictly. The dosage can be increased or decreased, depending on the doctor's advice.