Children—Use is not recommended. Use only the brand of this medicine that your doctor prescribed. These include itraconazole Sporanox, Tolsura , ketoconazole Extina, Ketozole, others and ritonavir Norvir. This medicine also works best when you take it an hour before sex on an empty stomach. You may take this medicine with or without food. Your doctor will probably start you on an average dose of vardenafil tablets and increase or decrease your dose depending on your response to the medication.Vardenafil may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away: headache; upset stomach; heartburn; flushing; stuffy or runny nose; flu-like symptoms; Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately: erection that lasts longer than 4 hours. Side effects of oral ED medicines are often mild. Common ones include: Flushing of the skin. Headache. Upset stomach. Visual changes, such as blue tinge to vision, sensitivity to light or blurred sight. Stuffy or runny nose. Back pain. Dizzy feeling. Get medical help right away if you have any very serious side effects, including: seizures, temporary memory loss. A very serious allergic reaction to this drug is rare.