The following nonprescription or herbal products may interact with sildenafil: cimetidine Tagamet HB , St. The body takes longer to absorb it after a high-fat meal or alcohol. If you are taking sildenafil for erectile dysfunction, you are unlikely to miss a dose since this medication is taken as needed, not on a regular dosing schedule. If you become pregnant while taking sildenafil, call your doctor. Sildenafil is in a class of medications called phosphodiesterase PDE inhibitors.Viagra generic form Viagra is a brand-name medication. It’s also available in a generic form called sildenafil. How does Viagra work and how long does it last? You may have . Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles . Sildenafil oral tablet is available as the brand-name drugs Viagra and Revatio. It’s also available as a generic drug. Generic drugs usually cost less than the brand-name .