With PAH, high blood pressure develops when a blockage in the arteries within the lung limits normal blood flow. It may increase your risk of dizziness or fainting. When using this medicine for erectile dysfunction, the ability to have sexual activity may be improved for up to 36 hours after taking the tablet. Do not change your tadalafil dose or stop taking this medicine without your doctor’s advice. Tadalafil works for these conditions by promoting muscle relaxation, which improves blood flow in PAH and urinary flow in BPH. In trials investigating Cialis, the majority of participants receiving the drug experienced a significant improvement in ED and maintained an erection. In BPH, the medication relaxes the urinary tract and bladder muscles, allowing for more effortless urine flow.CIALIS for Use as Needed. Creatinine clearance 30 to 50 mL/min: A starting dose of 5 mg not more than once per day is recommended, and the maximum dose is 10 mg not more than once in every 48 hours. Creatinine clearance less than 30 mL/min or on hemodialysis: The maximum dose is 5 mg not more than once in every 72 hours [see . What is Cialis? Cialis relaxes muscles of the blood vessels and increases blood flow to particular areas of the body. Cialis is used to treat erectile dysfunction (impotence) and symptoms of benign prostatic hypertrophy (enlarged prostate).  · Cialis; Descriptions. Tadalafil is used to treat men who have erectile dysfunction (also called sexual impotence). Tadalafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where .