What should I do if I forget a dose? Soon, in , ICOS received a patent for compound IC structurally unlike sildenafil and vardenafil , and Phase 1 clinical trials began in It belongs to the drug class known as PDE5 inhibitors. Do not take a double dose or more than one dose per day to make up for a missed one. Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient. What Is Cialis? Avoid eating a large meal or a lot of food, as this can slow down the effects of the drug.Cialis (tadalafil), for instance, is one of the most popular brand-name ED medications, and it is manufactured by Eli Lilly. Cialis can cost around $ to $ per month out of pocket, depending on the dosage you need. The first generic version of Cialis was released in October , and other manufacturers have released generic versions .  · The typical dose for once-daily Cialis for ED is milligrams (mg) to 5 mg. When used as needed for ED, the usual Cialis dose is 10 mg (with a maximum daily dose of 20 mg). The typical dose of. How Cialis Works. Tadalafil and other PDE5 inhibitors primarily work by inducing muscle relaxation. Tadalafil stops the breakdown of a chemical responsible for relaxing muscles. In ED and PAH, the drug targets muscle cells in blood vessels. When the blood vessel muscle cells relax, this expands the vessel and increases blood flow; this .