A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow. It added further: “As a matter of policy and sound statutory interpretation, patentees cannot be allowed to ‘game’ the system in this way. John’s wort. Before taking sildenafil, tell your doctor and pharmacist if you are allergic to sildenafil, any other medications, or any of the ingredients in sildenafil tablet or suspension. These include itraconazole Sporanox, Tolsura , ketoconazole Extina, Ketozole, others and ritonavir Norvir. The patent was published in and expired in If you become pregnant while taking sildenafil, call your doctor.The active drug in Viagra is sildenafil. It belongs to a group of drugs called phosphodiesterase-5 inhibitors. If you’ve had an allergic reaction to Viagra or any of . Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes . Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial .