Also Known As: Cialis, Tadalafil, Tadacip
Tadalafil is a PDE5 inhibitor, currently marketed in pill form for treating erectile dysfunction(ED) under the name Cialis; and under the name Adcirca for the treatment of pulmonary arterial hypertension. On 10.2011 FDA approved Cialis for treatment the signs and symptoms of benign prostatic hyperplasia (BPH) as well as a combination of BPH and erectile dysfunction (ED) when the conditions coincide. It initially was developed by the biotechnologycompany ICOS, and then again developed and marketed world-wide by Lilly ICOS, LLC, the joint venture of ICOS Corporation and Eli Lilly and Company. Cialis tablets, in 5 mg, 10 mg, and 20 mg doses, are yellow, film-coated, and almond-shaped. The approved dose for pulmonary arterial hypertension is 40 mg (two 20-mg tablets) once daily.
Tadalafil is also manufactured and sold under the name of Tadacip by the Indian pharmaceutical company Cipla in doses of 10 mg and 20 mg.
Although sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis) all work by inhibiting PDE5, tadalafil's pharmacologic distinction is its longer half-life (17.50 hours) – compared to Viagra (4.0–5.0 hours) and Levitra (4.0–5.0 hours) – resulting in longer duration of action, and so partly responsible for "The Weekend Pill" sobriquet. Furthermore, the longer half-life is the basis for current investigation of tadalafil's daily therapeutic use in relieving pulmonary arterial hypertension. Currently, sildenafil (trade name Revatio) is approved in several world regions as a thrice-daily therapy for pulmonary arterial hypertension.
Penile erection during sexual stimulation is caused by increased penile blood flow resulting from the relaxation of penile arteries and the smooth muscle of the corpus cavernosum. This response is mediated by the release of nitric oxide (NO) from nerve terminals and endothelial cells, which stimulates the synthesis of cGMP in smooth muscle cells. Cyclic GMP relaxes smooth muscle and increases blood flow to the corpus cavernosum.
Tadalafil, sildenafil, and vardenafil all act by inhibiting the PDE5 enzyme. These drugs also inhibit other PDE enzymes. Sildenafil and vardenafil inhibit PDE6, an enzyme found in the eye, more than tadalafil. Some sildenafil users see a bluish tinge and have a heightened sensitivity to light because of PDE6 inhibition. Sildenafil and vardenafil also inhibit PDE1 more than tadalafil. PDE1 is found in the brain, heart, and vascular smooth muscle. It is thought that the inhibition of PDE1 by sildenafil and vardenafil leads tovasodilation, flushing, and tachycardia. Tadalafil inhibits PDE11 more than sildenafil or vardenafil. PDE11 is expressed in skeletal muscle, the prostate, the liver, the kidney, the pituitary gland, and the testes. The effects on the body of inhibiting PDE11 are not known.
On November 21, 2003 the Food and Drug Administration approved tadalafil (as Cialis) for sale in the United States as the third ED prescription drug pill (after sildenafil citrate (Viagra) and vardenafil (Levitra)). Cialis's 36-hour effectiveness earned it the nickname, "The Weekend Pill"; like sildenafil and vardenafil, tadalafil is recommended as an 'as needed' medication. Cialis is the only one of the three that is also offered as a once-daily medication.
Moreover, tadalafil was approved in May 2009 in the United States for the treatment of pulmonary arterial hypertension and is currently under regulatory review in other regions for this condition. In late November 2008, Eli Lilly sold the exclusive rights to commercialize tadalafil for pulmonary arterial hypertension in the United States to United Therapeutics for an upfront payment of $150 million.