If used together, your doctor may change the dose or how often you use this medicine, or give you special instructions about the use of food, alcohol, or tobacco. Your doctor may adjust your dose if needed. Vardenafil usually works for 4 to 5 hours. Medicines that block an enzyme called CYP3A4. These medicines are called PDE5 inhibitors. Check with your doctor immediately if any of the following side effects occur: Less common burning feeling in the chest or stomach burning, crawling, itching, numbness, prickling, “pins and needles”, or tingling feelings cloudy or bloody urine.Do not give this medicine to anyone under 18 years old without medical advice. Viagra pregnancy and breastfeeding warnings (more detail) Stop taking Viagra and get . The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 . Viagra is approved for this use in males ages 18 years and older. Viagra contains the drug sildenafil. It belongs to a class of drugs called phosphodiesterase type 5 (PDE5) .