The dosage of sildenafil is different for each person and depends on the condition being treated with it. If you have ED, your doctor will give you a prescription for the right dose and a schedule to follow. If you have PAH, your doctor will probably prescribe you the same dose of sildenafil that you would take for ED. You will most likely need to take it at specific times throughout the day, and you should space your doses about 4 to 6 hours apart. Your doctor will check your progress regularly while you are on this medication to make sure it is working properly for you. If you miss a dose, take it as soon as you remember, but do not try to catch up by taking a double dose. Fildena 150 can cause side effects such as stomach bleeding or ulcers, and small holes in the lining of your gut (abdomen). These problems are rare but can be fatal. People with sickle cell anemia are at higher risk of these problems when they take this medication. They should also let their doctor know if they have ever had stomach or intestinal bleeding or a hole in their digestive tract.