In case of overdose, patients should receive supportive care. Keep from freezing. Avanafil Stendra. Do not use this medicine if you are also using a nitrate medicine, often used to treat angina or high blood pressure. Sildenafil may cause side effects. May make this condition worse. The usual adult dose is 20mg taken 3 times a day.The dose can be increased to mg or decreased to 25mg depending on its effect. Take sildenafil up to 4 hours before you want to have sex. For sildenafil to work properly, you’ll need to be sexually excited. Dosage and strength for pulmonary hypertension. Sildenafil tablets for pulmonary hypertension come in 10mg and 20mg strengths.  · The effects may be increased because of slower removal of the medicine from the body. Leukemia (blood related cancer) or. Multiple myeloma (blood related cancer) or. Sickle-cell anemia (blood disorder)—Sildenafil should be used with caution in these patients as problems with prolonged erection of the penis may occur. Sildenafil is available as oral tablets of 25 mg, 50 mg, and mg strength for erectile dysfunction (ED). Most patients receive a prescription for 50 mg of oral sildenafil, taken as needed approximately 1 hour before sexual activity. The dose can be titrated upward to a maximum of mg or down to 25 mg based on individual .