When the blood vessel muscle cells relax, this expands the vessel and increases blood flow; this effect is referred to as vasodilation. Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Soon, in , ICOS received a patent for compound IC structurally unlike sildenafil and vardenafil , and Phase 1 clinical trials began in Follow your doctor’s directions carefully, and ask your doctor or pharmacist to explain any part you do not understand. Most men start with and respond well to the 10 mg tadalafil dose. In trials of the drug, individuals taking Cialis saw a significant reduction in the frequency and urgency of urination and improved urine flow. Tadalafil has been extensively studied for ED.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 . Tadalafil (Cialis) is available in generic and brand versions in several doses as an oral tablet. You can take Cialis as needed or once a day, depending on the dose and how it’s prescribed. The maximum dose is 10 mg not more than once in every 48 hours. CrCl less than 30 mL/min or on hemodialysis: The maximum dose is 5 mg orally once every 72 hours. Once a day use for ED: CrCl 30 mL/min or greater: Data not available. CrCl less than 30 mL/min or on hemodialysis: Not recommended. Once a day use for BPH.